Wp7 guide for android developers

Microsoft 6/6/2011

Rev 1.0

Windows Phone 7

Guide for Android

Application

Developers

Windows Phone 7 Guide for Android Application Developers

2

About this Document ............................................................................ 4

Target Audience ................................................................................... 4

Conventions Used in this Document ........................................................ 4

Chapter 1: Introducing Windows Phone 7 Platform to Android Application Developers .......................................................................................... 5

The Developer Tools ........................................................................... 5

Windows Phone 7 Architecture ............................................................. 5

Comparing the Programming Stack of Windows Phone 7 with Android ...... 7

Summary ........................................................................................ 11

Related Resources ............................................................................ 11

Chapter 2: User Interface Guidelines..................................................... 12

Designing the Application Interface .................................................... 13

Application User Interface Design ....................................................... 14

Comparing Windows Phone 7 and Android Navigation ........................... 18

Windows Phone 7 Frame and Page Structure ....................................... 19

Application Templates ....................................................................... 21

Summary ........................................................................................ 21


Chapter 3: The Developer and Designer Tools ........................................ 23

A Comparison of Android and Windows Phone 7 Tools .......................... 23

Development Life Cycle and Windows Phone 7 Developer Tools ............. 24

The UI Design Tools ......................................................................... 26

Building Applications ........................................................................ 33

Debugging ...................................................................................... 34

Summary ........................................................................................ 38

Chapter 4: C# programming ................................................................ 39

Managed Programming ..................................................................... 40

A Comparison between C# Features and Java Classes .......................... 41

A Comparison of Important Class Libraries .......................................... 51

The New features of C# .................................................................... 54

Comparing API Documentation Tools .................................................. 58

NDoc .............................................................................................. 58

NDocs vs. Javadoc ........................................................................... 61

Summary ........................................................................................ 61



3

Chapter 5: A Comparison of Application Life Cycles in Windows Phone 7 and Android ............................................................................................. 63

Multitasking in Android and Windows Phone 7 ...................................... 63

Tombstoning of Applications in Windows Phone 7 ................................. 64

Life Cycle of a Windows Phone 7 Application ........................................ 64

Role of Handlers in an Application‟s Life Cycle ...................................... 66

Comparing Life-cycle Methods ........................................................... 68

Tombstoning and Windows Phone 7 Life Cycle ..................................... 69

Summary ........................................................................................ 74


Chapter 6: Storing Data and Preferences ............................................... 75

Isolated Storage in Windows Phone 7 ................................................. 75

Use Cases ....................................................................................... 78

Managing the IsolatedStorage Space .................................................. 79

Why Windows Phone 7 Does Not Use External Storage ......................... 80

Managing Content across Applications ................................................ 81

Comparing Intent API with Launchers and Choosers API ....................... 82

Summary ........................................................................................ 85


Chapter 7: XML Parsing in Windows Phone 7 and Android ........................ 86

XML Parsing in Windows Phone 7 ....................................................... 86

XML Namespaces for Windows Phone 7 ............................................... 86

XML Parsing Using XMLReader ........................................................... 86

TRAVERSING XML ............................................................................ 95

Summary ........................................................................................ 99



4

About this Document

If you have been developing Android applications and are interested in building your applications for Windows Phone 7, this guide is for you.

The guide covers what you need to know to add Windows Phone 7 development to your skill set, while leveraging what you have already learned building Android

applications.

Target Audience

This document is for Android application developers willing to develop applications

for Windows Phone 7.

Conventions Used in this Document

Term Abbreviation

Windows Phone 7 WP7

Application Programming Interface

API

Integrated Development Environment

IDE


5

Chapter 1: Introducing Windows

Phone 7 Platform to Android

Application Developers

Ever since the release of Windows Phone 7 (WP7) platform, developers from around the globe rushed to develop applications for this platform. Now, WP7 devices are

available with manufacturers all over the world. A large number of applications are already available in the WP7 marketplace.

For WP7, Microsoft went back to the drawing board to figure out what phone users really want, and built a phone from the ground up. The operating system, the user experience, and the application development platform have all been engineered

with users in mind. The revenue opportunities in the Windows Phone marketplace, accompanied by a great set of development tools, make WP7 a very attractive

destination for developers to build applications and games.

The Developer Tools

Microsoft recommends using these tools for WP7 application development. This toolset is free and can be downloaded from here. The toolset includes:

An IDE (for developers): Visual Studio Express for Windows Phone

A user interface design tool (for designers): Express Blend for Windows

Phone Silverlight for Windows Phone and XNA Game Studio for Windows Phone Windows Phone 7 emulator to test and debug applications

The tools are designed to let you develop consumer applications, business applications, and games.

Windows Phone 7 Architecture

WP7 utilizes a layered architecture. Like Android OS, WP7 runs on multiple phones. To provide a consistent user experience and features that you can rely on, WP7

defines a minimum set of hardware specifications that all phones must meet. They include:

ARM7 CPU

A DirectX capable GPU Camera

Multi-touch capacitive display Standard sensors include:

o A-GPS

http://create.msdn.com/en-us/home/getting_started


6

o Accelerometer

o Compass o Proximity and light sensors

There are three standard buttons on the phone: Back, Start, and Search. As we will see in a subsequent section, these buttons provide an easy and natural navigation model for the user.

In WP7, Microsoft provides most of the device driver code. A device manufacturer has to write very little code specific to their device. This improves the consistency

and quality across various devices. WP7 takes advantage of hardware acceleration through encapsulation layers, such as DirectX or XNA.

WP7 applications use managed programming and run within sandboxed

environments. For more details about WP7 architecture, watch the MIX‟10 presentation by Istvan Cseri, a WP7 architect.

http://live.visitmix.com/MIX10/Sessions/CL18



7

Comparing the Programming Stack of Windows Phone 7

with Android

The Application Model shown above provides services, such as installation and

update, for managing the application lifecycle. The UI model helps to manage application user interface. Applications are built using various WP7 frameworks.

This table gives an overview of the WP7 frameworks that provide features comparable to the Android programming layers.

Android

Frameworks

Functionality Windows Phone 7

Frameworks

Android Application Framework

Application UI, Device

integration (sensors, camera)

Windows Phone 7 Phone

Framework, Silverlight controls

Android Application

Framework Graphics, Animation, Media

XNA for games or Silverlight media and graphics for others

Android Libraries Base services, Networking, Text, XML, storage

Common Base Library

Android runtime (Dalvik)+ Linux kernel

Windows Phone 7


8

Android and Windows Phone 7 Stacks Side by Side

This table compares the Android and WP7 Frameworks side by side.

Managed Code

In Android, every application runs in its own process, with its own instance of the

Dalvik virtual machine. WP7 only supports “managed code” applications using C# or VB.net; there is no native access available to the system or the phone hardware.

.NET Common Language Runtime (CLR) manages the execution of such code. CLR provides garbage collection and there is no memory management to worry about or pointers to take care of. The WP7 application stack is built on the .NET compact

framework 3.7. As Dalvik virtual machine is optimized for mobile devices, the .NET compact framework is optimized for resource constrained devices and is designed

to be portable across various hardware platforms.

Android Frameworks Windows Phone 7 Frameworks

Applic

atio

n U

I and P

hone

Multi-tasking

Java

C#

or V

B.N

ET

Applic

atio

n

UI a

nd P

hone

inte

gra

tion

Application UI Application UI

Device integration Device integration

Browser Control Browser Control

Notifications Notifications

Peer to Peer Gaming

Silv

erlig

ht

Gamer Services

XN

A

Tw

o A

pplic

atio

n T

ypes

Controls & Gestures

Controls & Gestures

Media

Telephony Media Media

Media Framework

Animations Animations Animations

Graphics Graphics Graphics

OpenGL-ES Isolated Storage

Content Core

Lib

rarie

s

File System

SQLLite

Base C

lass

Lib

rary

Location Location

XML XML, LINQ

Networking Networking, Windows Communication Foundation

Libc, Dalvik VM CLR Base Classes

Android runtime + Linux kernel

Windows Phone 7 OS

http://blogs.msdn.com/b/brada/archive/2004/01/09/48925.aspx


9

Base Services

WP7 Base Class Library classes roughly correspond to those provided in the Android

Core Libraries.

Android core libraries include: Media framework for audio and video codec support

SQLite for database Opengl-ES

SGL for graphics and animation Networking stack Libc for embedding with Linux kernel

Dalvik VM

The WP7 Base Class Library layer also includes:

Networking stacks: such as HTTP and the Windows Communication Foundation (WCF). WCF provides an easy interface with XML and SOAP services across the Web, with features supporting the XML data transfer,

serialization, deserialization and XML parsing. Database support: WP7 does not have a local database, such as SQLLite.

You can write SQL-like queries in C# using Language Integrated Query (LINQ) to query XML data, stored in isolated storage (see below), or in remote databases such as SQL Azure.

Application UI and Device Integration

You can develop WP7 applications using two libraries: Silverlight and XNA. Silverlight contains the visual components same as Android standard widgets.

Generally, it is recommended that you use Silverlight for consumer or business

applications and XNA for games. However, you can certainly develop great games using Silverlight animation.


10

Android applications Windows Phone 7 counterparts

UI using activity(contains widgets) with navigation

between them

Silverlight applications with pages connected by flows

2D or 3D games built

with Opengl-ES

XNA games with 2D / 3D graphics

and Xbox connectivity

XNA for Games

For a high performance game, XNA is the right option. XNA framework, originally developed for XBOX, provides hardware accelerated 2D and 3D rendering and bitmap graphics. XNA also provides gamer services such as authentication and

connectivity with XBOX Live, as well as Profiles and Leaderboards.

Silverlight Controls and Media

If you use Android activities and widgets, you will find a large set of Silverlight UI controls specifically designed for the OS. WP7 UI components are designed for

multi-touch. Silverlight uses a declarative language called Extensible Application Markup Language (XAML) to specify user interfaces. You can use separate code-

behind files, written in C# or VB.NET, to respond to events or manipulate the controls.

Silverlight provides high performance audio and video with variety of CODECs. It

supports both vector and bitmap graphics with hardware acceleration. As opposed to a file system, Silverlight provides sandboxed storage, called isolated Storage, to

store the application-specific data. With the isolation of storage, one application cannot affect other applications that are running on the phone.

Windows Phone Frameworks

If you need to use HTML in your application, you can use the Internet Explorer

based browser control in your application for HTML UI. Windows Phone Framework layer also provides interfaces to various sensors, such as the accelerometer or the


11

camera. Microsoft provides a push notification service, called Microsoft Push

Notification Service.

In Android, multitasking is supported. In WP7, support for multitasking will be

provided in the next release. In Android, you need to use third-party platforms like ADMob to publish advertisements in applications. Microsoft has made this task easier in WP7 by introducing Microsoft Advertising SDK for WP7.

For more information, visit:

Microsoft Advertising SDK for Windows Phone 7

Summary

In this chapter we looked at the WP7 architecture and the Android and WP7 programming stacks. Now that you have a high-level idea of how the WP7 programming stack maps to the Android stack, we are now going to go one level

deeper. In the next section, we will look at the user interface guidelines of WP7 applications.

Related Resources

To learn more about the topics covered in this blog, visit:

App Hub – Central Place for Windows Phone 7 development. Getting started,

download tools and read all about Windows Phone 7 development MIX ‟10 presentation on Windows Phone 7 Architecture by Istvan Cseri Windows Phone 7 Development for Absolute Beginners. Video series that will

help aspiring Windows Phone 7 developers get started. App Hub Jump Start Tutorials

Introduction to WP7 programming on Codeproject.com

Other Resources you may find useful:

Overview of the Windows Phone 7 Application Platform

Windows Phone 7 Team Blog Windows Phone 7 Programming

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=b0f00afc-9709-4cc2-ba2c-57728db6cbd6



http://channel9.msdn.com/Series/Windows-Phone-7-Development-for-Absolute-Beginners

http://create.msdn.com/en-US/education/catalog/article/wp7_jump_start

http://www.codeproject.com/Articles/108022/Introduction-to-Windows-Phone-Programming-Part-1.aspx


http://www.microsoft.com/windowsphone/en-us/default.aspx

http://msdn.microsoft.com/en-us/library/ff402535(v=VS.92).aspx


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Chapter 2: User Interface Guidelines

Microsoft‟s Windows Phone 7 (WP7) uses a novel user interface called Metro. WP7 sets itself apart with its clean and simple design and emphasizes on color and typography.

In contrast to the application-focused design of Android, WP7 uses an information-centric design. Instead of an array of application icons, the start screen of a WP7

consists of dynamic tiles that display critical information at a glance to the user. The tiles are dynamic and they continuously display the up-to-date status of the applications. For example, they show you the next appointment on your calendar,

or the number of new emails waiting for your attention. Users can personalize their phones by pinning the tiles that they care most about.

WP7 introduces a new paradigm called hubs. Hubs bring related information together. There are six hubs, People, Pictures, Music + Videos, Marketplace, Office, and Games. The People hub, in the instance shown below, aggregates your address

book contacts and Facebook friends.

http://www.microsoft.com/windowsphone/en-us/features/default.aspx#start-screen-live-tiles

http://www.microsoft.com/windowsphone/en-us/features/default.aspx#people-hub


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Designing the Application Interface

While the design of the WP7 user interface is different from that of the Android, the

core design principles are very similar. Like Android, in WP7 you need to keep in mind the compact screen, lower CPU, and limited memory while designing the

applications. In WP7, users use one application at a time, with just one screen visible.

Similar Application Design Goals

Usability and UI design are not after thoughts, but are the primary goals behind

applications on both the Android and WP7. Applications need to be simple and focus on key scenarios that most users care about.

Visual Elements and Direct Manipulation

Like Android, visual elements and direct manipulation of objects by touch are the

key characteristics of the WP7 application. WP7 provides a complete set of UI controls designed for the phone.

WP7 utilizes the same set of core multi-touch gestures as the Android with similar

semantics, these include: tap, double tap, pan, flick, touch and hold, and pinch and stretch.

Implications of the Similarities for the Developers

For the most part, the application planning process is similar on both the platforms.

While designing your WP7 application, you will focus on the same information that is critical to the user. Your key design principles from the Android application will

get carried over: metaphors and direct manipulation with multi-touch. The need for immediate feedback and aesthetic appeal remains the same.


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Application User Interface Design

While there are similarities in the design principles of the applications on both

platforms, pay close attention to the user interface of the application for the WP7. It is best to take advantage of the unique features and strengths of WP7 platform.

For the interface to provide a consistent experience across applications, applications on WP7 need to adopt the new Metro design guidelines.

XML and XAML

Android uses XML for mapping purposes. A part of the compilation reads the XML,

performs translations, and generates Java. For example, in layout XMLs of Android, you need to set it as content view in Activity, after defining the whole UI.

In WP7, XAML act as an instantiation language. XAML does not act as a mapping

medium in WP7 as XML does in Android. The XML in a XAML document in WP7 contains the actual code needed for UI and needs not be transformed into code, as

in case of Android.

Controls and the Application Interface

The WP7 development tools and SDK include a rich collection of Silverlight controls that are designed specifically for usability and aesthetics. While you can create your

own controls, it is best to use the standard controls wherever possible. These standard controls respond to theme changes and provide a consistent user interface.

The following table shows the mapping between WP7 Silverlight controls and corresponding Android controls.

Android control Windows Phone 7 control

Border Border

ButtonView Button

AbsoluteLayout Canvas

CheckBox CheckBox

GridView Grid

HyperlinkButton

ImageView Image

ListView ListBox

MediaController MediaElement

http://go.microsoft.com/fwlink/?LinkID=183218


http://go.microsoft.com/fwlink/?LinkId=206535









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MultiScaleImage

ViewGroup Panel

EditText PasswordBox

ProgressBar ProgressBar

RadioButton,

RadioGroup

RadioButton

ScrollView ScrollViewer

SeekBar Slider

LinearLayout StackPanel

EditText TextBlock

EditText TextBox

MapView Map

WebView WebBrowser

Panorama

Pivot

TimePicker Timepicker

DatePicker Datepicker

ExpandableListView

Gallery

ImageSwitcher

Spinner

TableLayout

TextSwitcher

ViewFlipper












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ZoomControl

TabHost

SlidingDrawer

RatingBar

Toggle button ToggleSwitch*

* ToggleSwitch and Datepicker/Timepicker control are part of the Silverlight for Windows Phone Toolkit available on Codeplex:

http://silverlight.codeplex.com/releases/view/55034

As you can see, WP7 offers controls that correspond to almost all Android controls.

While the look and feel is different, they provide similar functionality.

New Controls in Windows Phone 7

WP7 introduces a few novel controls that have no counterpart on the Android. Here are some of the examples:

A multi-scale image, with image data at various resolutions, is appropriate for allowing the user when zooming into a photo.

Panorama control is a multi-screen page and allows a page to span

horizontally beyond the width of the phone. The people hub is another great example. It allows a large amount of related

information to be presented. Pivot control, a novel control that is useful to manage views and display

information that is logically divided in sections.



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Notifications

Both Android and WP7 have notification services, but notifications play a key role in WP7. The tiles are used to display non-critical information without disrupting what the user is doing. If you are using status bar notifications in Android, you can use

tile notification as a replacement in WP7 to show critical information.

The notification service also display toast notifications that provide time sensitive

information, such as an SMS. The toast notifications are shown for about 10 seconds, but the user may choose to ignore them. These are the same as Android toast notification.

Android Functionality Windows Phone 7

Status bar

notification

Non-critical information that user

may not respond to. That is informative to user

Tile notifications

Toast notification

Time sensitive data that user may not respond to

Toast Notifications

Alerts Modal alerts that the user must respond to

Application notifications


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Tool and Tab Bar vs. Application Bar

WP7 features a versatile application bar. The application bar can include up to 4 of the most common views or application tasks. You can also use application bar

menus for additional context-sensitive tasks. If you are using action sheets in your Android application, application bar menus give you similar functionality.

Android Functionality Windows Phone 7

Status bar Information about

device

Status bar

Title bar: to show title

of application or activity

Navigation, Title,

Buttons for views or actions

Back button for back

navigation

Page title

View and actions on Application bar

Comparing Windows Phone 7 and Android Navigation

WP7 application is a collection of multiple pages. Like on the Android, the user navigates through different Activities using widgets such as buttons and links.

Like Android, on WP7 the Back button on the phone allows the user to navigate back between pages within an application, or across applications. It behaves much

like the Back button in a browser. The Back button also closes menus and dialogs. As a developer, you should consider what the Back button means to your user and plan to override it appropriately. For example, you may decide to pause a game by

using the Back button on the Phone.

The other two hardware buttons on the WP7 phone, namely, Search and Home,

have fixed behavior.


19

Windows Phone 7 Frame and Page Structure

Each WP7 application has a single frame, and it includes areas for:

A page where application content is rendered. This is the content where widgets or graphics are rendered.

A reserved space for the system tray and application bar. It also exposes certain properties, such as orientation to the application.

System Tray and Application Bar

On WP7, the system tray includes indicators for various system-level status

information. The application bar includes the area for the most common application menus, which may include various data views or tasks.


20

Page Structure of Windows Phone 7 Application

The following diagram shows the structure of a typical WP7 data-bound application,

which resembles a navigation-based Android application.

When the user first starts the application, he or she is presented with a splash screen, designed to welcome the user, as well as to create the perception of fast response. Splash screens are usually an image file of the entire size of the display.

Usually the application starts with the home page, the main navigation page, with links for search, and other page widgets. Consider an application that shows

information about baseball teams and their players. The primary content page, marked as the widgets page in the above diagram, have the content of interest. For

example, a list of all baseball teams. However, depending on requirement, the home page can also be the primary content page.

This is a possible application usage scenario:

A user clicks one of the team links to visit the team details page (“Widget Details Page”) which can provide multiple views. The team details page may

employ a pivot control or panorama to display different views such as the team summary and the list of all players (“List of Gadgets Page”) from that team

A user selects one of the baseball players and the application takes the user

to the page with player statistics (“Gadget Details page”). The player statistics page uses controls such as textblocks, multi-scale images, or other multimedia using a MediaElement control

A user can also use the search widget to search and directly access the team

page (“Widget Details Page”) or the player page (“Gadget Details Page”)


21

Application Templates

Eclipse does not provide the project template for Android applications. But Visual

Studio provides numerous templates for WP7 application development to make your life easier.

Functionality Visual Studio Template Eclipse

Information drilldown

applications

Data-bound applications Not available

Utility applications. For

example, Bubble Level

Windows Phone 7 utility

applications

Not available

Games Windows Phone 7 Game

(XNA) applications

Not available

Flexible template to design

any application

General Windows Phone 7

applications

Not available

You can choose the Windows Phone application template to either create an

application with functionality similar to the view-based or the window-based Android application type. Lastly, the XNA based games application template gives

you functionality like the OpenGL-ES application.

Summary

In this chapter we looked at the similarities between the application design goals of the Android platform and the WP7 platform. When you plan your WP7 application,

you will be able to leverage your existing work on Android applications.

We also looked at the application interface design to make sure you are taking

advantage of the WP7 metro design that uses WP7 interface guidelines. You will find that the WP7 tools offer a large library of controls and gestures that have close counterparts on the Android.

This chapter also showed you the use of innovative controls like panorama, and explore the use of live tiles to build an engaging WP7 experience.

Related Resources

To go deeper into the topic discussed, visit:

Windows Phone 7 User Interface Guidelines

Windows Phone 7 Developer Tools Silverlight for Windows Phone toolkit on CodePlex Design resources for Windows Phone

http://go.microsoft.com/fwlink/?LinkID=183218



http://msdn.microsoft.com/en-us/library/ff637515(VS.92).aspx


22

Other Resources that you may find useful:

Application Page Model for Windows Phone 7 Frame and Page Navigation Overview for Windows Phone

http://msdn.microsoft.com/en-us/library/gg278407(v=VS.92).aspx



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Chapter 3: The Developer and

Designer Tools

With the release of the Windows Phone 7 (WP7) developer tools, Microsoft brings the user-friendly, high productivity Visual Studio Development environment to WP7.

As Android application developers you are familiar with Eclipse, and you can quickly migrate to WP7 developer tools and work with ease.

A Comparison of Android and Windows Phone 7 Tools

Visual Studio 2010 Express for Windows Phone is a full-featured Integrated

Development Environment (IDE). Visual Studio 2010 facilitates designing, developing, and debugging of Windows Phone 7 applications. The other WP7 tools

that help you in the development cycle of the Windows Phone application are:

Expression Blend XNA Game Studio

Windows Phone Emulator

The WP7 developer tools offer the complete functionality that is provided by the

Android application developer tools. The following table gives an overview of the functionality of each of these tools. The table also indicates the equivalent tools you use for Android application development.

Functionality Audience Android

tools

Windows Phone 7 tools

Primary UI design: Colors, gradients, and

animation

UI designers Defined in XML, any XML tool

Expression Blend

UI design UI designers

and programmer

s

ADT UI

plug-in Third-

party tool like DroidDraw

Visual Studio 2010 Express

and Expression Blend for Windows Phone

Application development

(coding)

Programmers Eclipse Visual Studio 2010 Express for Windows Phone

Game

development

Programmers Eclipse XNA Game Studio


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You can use the Android team structure and overall development process to build applications for Windows Phone 7. The WP7 toolset ensures that the entire team of

designers, developers, and testers familiar with Android development tools will find it easy to migrate to the WP7 toolset.

Development Life Cycle and Windows Phone 7 Developer

Tools

Expression Blend 4 and Visual Studio facilitate a close collaboration between designers and developers.

Both these tools share the same file structure and source files. Expression Blend uses XAML for UI design and the XAML is consumed by Visual Studio. This system allows separation of responsibilities between the designer and the developer while

allowing them to work together seamlessly.

Project Management for Windows Phone 7

Like Eclipse, Visual Studio 2010 Express for WP7 is a fully-featured IDE. Visual

Studio 2010 Express allows you to:

Manage the entire structure of the development project, the source, and the

resource files Configure the application codebase, known as Visual Studio Solution, as a

collection of projects in a separate functional unit

With Visual Studio 2010 Express, you can manage source files, share code, and manage the work among team members. Visual Studio integrates a compiler and a

(coding)

Testing / Emulation

Testers Android Emulator

Windows Phone Emulator in Visual Studio 2010 Express


25

debugger. You can access both the compiler and the debugger either from the GUI

or the command line.

To create a sample application, do the following:

1. Start Visual Studio Express for WP7 from Start menu.

2. In Visual Studio Express, click File.

3. Click New Project.

4. In the New Project dialog box, select Windows Phone Application.

5. In the Name of the project text box, enter ShoppingList as the name of

the project, and click OK. Visual Studio Express creates the new project.

The Solution Explorer pane displays the solution that you created. This example solution has only the ShoppingList project. The project contains the sources,

resources, and properties.

Note: Visual Studio Express for WP7 does not provide integration with source

control systems. The Visual Studio Professional edition provides features such as integration with various source control systems like Subversion. You can also use

Visual Studio Team System, which is designed for greater communication and collaboration among the development teams.


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The UI Design Tools

The WP7 developer tools include:

Expression Blend Visual Studio UI Designer

WP7 uses Silverlight and a specific XML markup language for the UI specification.

Visual Studio UI design tool is equivalent to the Eclipse ADT UI plug-in. As Android application developers you are familiar with Eclipse ADT UI plug-in and you will find

it easy to use this tool. In our example, the main page for the ShoppingList solution, MainPage.xaml, is already open in the Visual Studio UI Designer tool for

editing.

To change the titles of the application and the current page, do the following:

1. Right-click the title MY APPLICATION and select Properties.

2. In the Properties window, select Text and enter SHOPPING LIST.

You can also change the title of the page by entering my list in the Text property of

the title.

To change the title of a page, do the following:

1. Drag a Text box from the Toolbox and place it above the textblock.

2. Update the Text box‟s Text property to delete any existing entry.


27

3. Below Properties, click TextBox1, and enter txtItem to change the ID of

the textbox to txtItem.

4. Resize the Text box by dragging its lower right corner so that its width is

300.

5. Drag a Button to the right of the TextBox.

6. Change the button‟s Content property to Add, and its ID to btnAdd.

7. Resize the button so that its width is 140.

8. Drag another TextBox and place it underneath the txtItem textbox.

9. Resize the new TextBox so that it covers the rest of the phone screen.

10.Update the ID of the new TextBox to txtList.

11.Update the Text property of the new TextBox to Nothing here yet!.

Your application looks as shown below:

12.To start debugging, compile the application and launch, press F5 or click Debug

The application starts the WP7 emulator, deploys, and runs the ShoppingList application. You can click Add. But the application does not respond because there

is no code for the button you inserted in the previous steps.


28

Note: You can use the context menus to add the event handlers or to set the control properties. The emulator‟s integration with Visual Studio allows for a direct manipulation of controls and makes it easy to add logic to the UI controls.

Expression Blend for Windows Phone 7

Expression Blend for WP7 is a visual UI design tool that is suitable for designers. There is no exact equivalent to Expression Blend in Android development toolset. Expression Blend is like VS Design. With Expression Blend, you can:

Drag and drop UI elements to design the UI You can layout the controls accurately up to pixels. You can easily create

and use color palettes and gradients Add special effects, such as reflections and shadows

Import Photoshop files and Android application resources to the Windows Phone application

Create fine application behavior and animations without any programming


29

Expression Blend is for UI designers and Visual Studio Design is for programmers. Programmers can also use Visual Studio Design to integrate the application logic to the UI design. You can also use the Visual Studio UI design tool to design UI for

applications.

Both Expression Blend and Visual Studio Design have:

A single control set that provides accurate fidelity to their run-time visual representation. This feature allows you to easily visualize the application.

Same project structure and share the same source files for designers and

developers. Use or produce XAML, which is a Silverlight XML declarative markup

language used for interface design. This feature allows a designer to work on the design using Expression Blend while the developer uses Visual Studio to design the logic behind the application. You can establish a smooth design

and development workflow.


30

Visual Studio

Visual Studio has a simple to use, full-featured, and a configurable source editor.

The editor tool has various features that are familiar to Eclipse users. The features of the editor include:

Flexible search

Rich editing Format code

Auto-completion of code Outline or hide code

To add logic to the application, do the following:

1. To stop the running application, click Debug.

2. Click Stop Debugging.

3. Double click Add. The dialog displays MainPage.xaml.cs with a method btnAdd.

4. Click the MainPage class.

5. To add logic to the items that are added to the shopping list, edit the

btnAdd_click method.

6. Enter the following code: string tStr = txtItem.Text;.

Note: When you enter t for txtItem, Visual Studio displays the auto-completion dialog box. The Visual Studio equivalent for Eclipse auto-completion is called content assistant.


31

7. Enter the following code in the btnAdd_click method:

if (!String.IsNullOrEmpty(tStr))

Note: When you type String, Visual Studio displays the auto-completion dialog box.

When you type Is, Visual Studio displays the class methods of the String class.

VS IntelliSense in Visual Studio

VS IntelliSense is a feature of the IDE which uses history, code context, and .NET reflection for intelligent auto-completion. VS IntelliSense can suggest and complete variable names, parameters, classes, and method names. VS IntelliSense can also

generate appropriate code where needed, as shown in the code below:

To complete the event hookup, Visual Studio generates an empty stub for the event handler button1_click method.


32

Code Snippets in Visual Studio

Code Snippets in Visual Studio is equivalent to code templates in Eclipse. Code

Snippets allows you to insert code fragments with a few clicks. Visual Studio contains a large number of snippets. These snippets help you to create their own snippets. You can also create an index and search for the code snippets by using

the self-defined terms.

To use a code snippet, do the following:

1. To start the Insert Snippet prompt, press CTRL+K CTRL+X

2. To insert a code snippet for an if statement in the code, select Visual C# followed by i

The inserted snippet shows the parts of the code that you need to complete.

private void btnAdd_Click(object sender, RoutedEventArgs e)

{

string tStr = txtItem.Text;


{

if (true)

{

}

}

3. To complete writing the code for the method, enter the required code so

that the body of the method is complete as follows:

string tStr = txtItem.Text;


{

if (txtList.Text == “Nothin here yet”)

{

txtList.Text = “”;

}

txtList.Text += txtItem.Text + “\n”;

txtItem.Text = “”;

}

Visual Studio supports various refactoring mechanisms. You can select any piece of

code and right-click the code to access the refactoring menu.


33

Visual Studio Editor

Visual Studio editor is customizable. Visual Studio editor allows you to define

various keyboard shortcuts or create your own macros. Macros help you to automate repetitive actions by combining a series of commands and instructions. You can easily customize Visual Studio Editor to use shortcuts and keyboard

combinations with which they are familiar.

Instead of opening a separate window for each file, as in Eclipse, the default view in

Visual Studio uses tabbed windows. You can change this behavior to suit your need. You can change the way in which various windows are docked within Visual Studio Shell.

Building Applications

Visual Studio Express for WP7 allows you to build the Visual Studio solution on demand. It allows you to separately build each project to make a part of the

complete solution.

Visual Studio uses an XML based, declarative build system called MSBuild. MSBuild is equivalent to Ant and Nant. You can access the builds either from the GUI or by

using the command line for batch processing. MSBuild is flexible and allows you to create a specific target either as a debug build or as a release build.

Windows Phone 7 Emulator

The WP7 Emulator provides a virtualized environment in which you can deploy, debug, and test applications. The WP7 Emulator is designed to provide a comparative performance of an actual device and meets the peripheral

specifications required for application development.

To access the WP7 Emulator from Visual Studio, do any of the following:

From Deploy menu, click Deploy Solution Press F5 in the key board, this starts the Emulator along with the debugger Press CTRL+F5, this start only the Emulator


34

The WP7 Emulator is like the Android Simulator. However, these differences are

there:

In Android emulator you can have access to all the system application like

Phone Dialer, Contacts, Mail, and Media Gallery. But the WP7 Emulator the system applications are not directly accessible to you. Though it can be accessed by the Launchers and Choosers.

Android supports various display height and width. Likewise, you can customize the Android emulator for parameters like Screen Height, Width,

RAM size, and Sensors. As WP7 have specific hardware requirements, you cannot modify the WP7 Emulator for these hardware parameters.

Debugging

Visual Studio Express Phone 7 includes a symbolic debugger that you can use with

the WP7 EMULATOR or with a remote device. Once the application loads in the debugger, you can view the variables in the application and control their execution.

To work with debugger, do the following:

1. To start the debugger, press F5

2. In Textbox you previously created, enter napkins and click Add. Refer to

the image below.

Note: napkins is added after Nothing here yet!

3. In Visual Studio, click the light blue area to the left of the string tStr =

txtItem.Text; line.

Visual Studio inserts a breakpoint at that line.


35

4. Launch the debugger again using F5. When the application loads into the debugger, rest the mouse pointer over txtItem in the code

5. Click + in the pop-up to view the variable txtItem.

Tracking Variables

You can view the details of the variables such as the Type, Fields, and Properties. The dialog below shows how you can scroll up and down the Type Hierarchy to

inspect the objects.

You can set a watch on certain variables to keep them under observation continuously.

To track variables, do the following:

1. Right-click txtList, and click Add Watch. The watch window displays the variable txtList.

2. Click + icon near txtList, to expand txtList.


36

3. To ensure that the control does not enter the if statement, press F10 to step

through the code.

if (txtList.Text == "Nothing here yet")

{

txtList.Text = "";

}

You can observe in the Watch window that the value of txtList.Text is Nothing here yet. But it gets compared with Nothing here yet (with no exclamation point.) This is

a bug in the code.

Change the statement as shown below to add the exclamation point:

if (txtList.Text == "Nothing here yet!")

Note: While in the debugger, you can use the VS immediate mode where you can

write the managed code instructions to modify or view the variables or execute code to help with debugging.

4. Update the code and re-launch the debugger by pressing F5.

5. To test the application, add items to the shopping list.


37

A Note about Debugging

You will observe that you can easily debug a WP7 application using the managed

programming environment. Like Eclipse, the debugging in WP7 application is done entirely at the application level using the C# code and types.

Note: The .NET framework includes two classes called Debug and Trace, which help you to write run-time debug messages to the output window. C# also supports an assert statement, which is evaluated at run time. If the statement returns true,

Visual Studio does not respond. But if the statement returns false, the program enters the debugger.


38

Summary

In this chapter we looked at the Windows Phone 7 Developer Toolset. The Toolset

includes the rich tools that are designed to support every step in the entire application development lifecycle. The design, development, and the testing tools

are equivalent to the existing Android team roles and processes. The tight integration between the WP7 tools helps you to streamline the design, develop the workflow, and test the workflow. These tools provide an end-to-end functionality

and are highly customizable.


39

Chapter 4: C# programming

This chapter discusses the C# features that map to the most common Java features. This chapter includes the code snippets, which help you to work faster with C# code. It describes important C# features that help you write safe code and

enhance productivity.

The chapter discusses the following features of C# programming:

Managed Programming Class Declaration Strong Typing

Class Constructors Properties

Parameter Types Access Privileges Methods with multiple Parameters

Inheritance Protected Access

Instance vs. Class Level Access Abstract Classes Interfaces

Polymorphism Structs

Object Lifecycle: Creation and Deletion of Objects Type Checking vs. Reflection Exception Handling


40

Managed Programming

WP7 supports managed programming in C# and VB.NET.

The C# compiler (and similarly, the VB compiler) compiles the C# (or VB.NET) code in an intermediate language (IL) byte code and metadata. The Common Language

Runtime (CLR) executes the bytecode. The C# uses metadata to manage type safety, exception handling, and array bounds. CLR also manages memory and performs garbage collection. In Android, the Java code is compiled in a .class file,

and the file is converted to a .dex file. The .dex file is optimized for low foot print on memory. The .dex file is then converted to an apk file, which is executed on an

android platform.

http://blogs.msdn.com/b/brada/archive/2004/01/09/48925.aspx


41

A Comparison between C# Features and Java Classes

Class Declaration

Like Java, C# does not separate class definition from class implementation. The

compiler derives the metadata about the classes from class implementation. As in Java we can define multiple class definition in same file. C# also defines the multiple classes in same file.

using System; // In java this is similar to import

namespace FirstApplication // scope for classes. Same like package declaration in Java

{

class Person // only uses class implementation

{

private DateTime birthDate; // a private field accessible to this class

private int ageOn(DateTime date) // a private method

{

TimeSpan span = date.Subtract(birthDate); //uses a .notation to invoke

return span.Days;

}

public int age // this is a property.

{

Get // just a getter; it’s a read-only property

{

return this.ageOn(DateTime.Now);

}

}

public Person( DateTime dob) // instance constructor. Same like Java

{ // it combines allocation and initialization

birthDate = dob;

}

}

class Program // Same like Java, another class in the same file.

{

static void Main(string[] args) // main entry point into the program

{

Person p = new Person(new DateTime(1973,11,12)); //construct an instance

System.Console.WriteLine("The age is is" + p.age.ToString());

DateTime dt = p.birthDate; //error in compilation birthDate is private

}

}

}

The following example shows the public signature of the class Person that consists of property, age, and constructor.

Instead of using the import statement in Java, C# employs a using statement to refer to the metadata of other classes. The namespace declaration that is shown at

the top of the file is used to declare the scope and to organize the code. You can access classes in other namespaces by referring to a fully-qualified name. You can refer to System.Console.WriteLine in the example above, where the console is in

the System namespace.

C# uniformly uses the “ ” notation for referring to all methods, fields, and

properties.

Strong Typing


42

C# is a strongly typed language like Java. The types must be specified for variables

and input/output parameters. The compiler enforces the types. In the section on generics, you can see how C# uses strong typing for collection classes.

Strong typing works similarly for all classes. The code example below shows the strong typing for primitive types.

int a = 5;

int b = a + 2; //OK

bool test = true; // OK

int c = a + test; // Error. Operator '+' cannot mix type 'int' and

'bool'.

Class Constructors

Like Java, C# uses instance constructors to create and initialize instances. For example: p is an instance of the Person class. You can construct and initialize p

with a given birthdate, in a single statement.

Person p = new Person(new DateTime(1973,11,12));

Properties

You often need to decide about whether to implement a member as a property or a method. In this case, the design pattern is identical for both Java and C#. As a general rule, use properties when you need to access data. To take any action on

the data, use methods.

Properties helps to abstract away from directly accessing the members of a class.

This technique is similar to using accessors (getters) and modifiers (setters) in Java. You can make the property read-only by providing the getter, write-only by providing the setter, or read-write by providing both getter and setter.

Parameter Types

Like Java, C# uses the value parameters by default. C# does not have pointers. But C# allows the passing of parameters by using the ref modifier. Instead of pointers, you can use parameters with ref where you want to achieve an additional

functionality in a method. In some cases, you need to use the reference parameters for better efficiency since they avoid data copying.

void Foo (ref int x, int y)

{

x = 0;

y = 0;

}

..


43

int a = 5;

int b = 8;

Foo (ref a, b);

//a is zero and b is still 8

C# also provides the parameters with an out modifier. This out modifier represents the parameters that must be initialized by the called method before returning. This

design pattern is often used to return the error in addition to the value of the function.

Access Privileges

Like Java, C# allows the access privileges on fields (for example, birthDate),

properties (for example, age) and methods (for example, ageOn). C# uses public, private, and protected as modifiers to denote the three different levels of access privileges.

In the above example, the compiler gives an error response on p.birthDate since that variable is private. Therefore p.birthDate is not accessible from the Program

class. Similarly, the ageOn method is also private and inaccessible from the Program class.

Methods with Multiple Parameters

Both Java and C# support methods with multiple parameters. While C# traditionally

uses positional and unnamed parameters, the latest version of C# has introduced the named parameters. The following example shows the comparative syntax for Java and C#.

Java C#

void addEmployee(string name, int

id, int age);

void addEmployee(string name, int

id, int age);

Off.addEmployee("Phil",2345, 23); Off.addEmployee("Phil",2345, 23);

Off.addEmployee(name: "Phil",

age:23, id:2345);

Like Java, C# explicitly supports method overloading. C# differentiates between the methods that have the same name by using information about the parameter

types. The following code sample shows how C# differentiates between methods that have the same name.

void insert (myClass obj, int index);

void insert (myClass obj, myClass before);

The method insert may be called with both these signatures:

list.insert (myObj1, 4);

list.insert (myClass obj, myClass before);


44

The following code sample shows another example of method overloading:

using System;

namespace SecondApplication

{

struct Point // In contrast Java where struct not

supported, C# structs are closer

{ // classes.

public double x; // struct fields can also have access

modifiers

public double y;

public Point(double p1, double p2) //a constructor for the struct

{

x = p1;

y = p2;

}

}

interface IThreeDShape // an interface, like an Java interface

{ // defines the behavior

double volume

{

get; // Volume is a read-only property. no

setter

}

}

abstract class Shape // this class is marked abstract, i.e. may

not be instantiated.

{

protected Point origin; //only derived classes may access

protected static int counter = 0; // Similar to protected variables in Java

public string ID;

protected Shape() //a constructor. Same name as the class

name

{

counter++; // class variable being updated

}

public Point Origin // similar to Java class

variables

{

set

{

origin = value;

}

}

public abstract double Area //denotes that this property must be

overridden

{ // in a derived class

get;

}

public abstract bool contains(Point p); // this method must also be

overridden

}

class Rectangle : Shape //Similar to Java, single iinheritance

{

public double length; //field accessible from others

public double width;

public Rectangle(Point o, double l, double w) //a public constructor

{

ID = "Rectangle_" + counter.ToString();

origin = o;

length = l; width = w;

}


45

public Rectangle(double l, double w) // one constructor using another

constructor

//creates a rectangle at the origin

: this(new Point(0, 0), l, w)

{

}

public override double Area // unlike Java, overridden method must

{ // use override keyword

get

{

return length * width;

}

}

public override bool contains(Point p)

{

if ((origin.x < p.x && origin.x + length > p.x) || (origin.x > p.x &&

origin.x - length < p.x))

if ((origin.y < p.y && origin.y + length > p.y) || (origin.y > p.y &&

origin.y - length < p.y))

return true;

return false;

}

}

class Square : Rectangle

{

public double side;

public Square(double s)

: base(s, s) //constructor

{

ID = "Square_" + counter.ToString();

side = s;

}

} class Cube : Shape, IThreeDShape //similar to Java, class implements

interface

{

public double side;

public Cube(double s)

{

ID = "Cube_" + counter.ToString();

side = s;

}

public override double Area

{

get

{

return 6 * side * side;

}

}

public double volume

{

get

{

return side * side * side;

}

}


…

}

class SecondProgram

{

static void printVolume(IThreeDShape tdShape)

{

Console.WriteLine("The volume is " + tdShape.volume);


46

} }

static void Main(string[] args)

{

Rectangle r = new Rectangle(5.0, 3.0);

Cube c = new Cube(4.0);

SecondProgram.printVolume(c);

double a = r.Area;

Console.WriteLine("The area of rectangle " + r.ID + " is " +

a.ToString());

bool b = r.contains(new Point(1, 2));

Console.WriteLine("The point is in " + b.ToString()); // will print

TRUE

}

}

}

Inheritance

Like Java, C# also uses a single inheritance mechanism. Inheritance is specified by

listing the parent class after the class name as shown below. In this example, the class Rectangle inherits from the class Shape, whereas the class Square inherits

from the class Rectangle.

class Rectangle : Shape

class Square : Rectangle

In C#, the constructor of the base class is automatically invoked when you construct an instance of a derived class. However, a derived class can invoke a

specific constructor of the base class if needed. This you can see in the constructor of the Square class.

public Square(double s): base(s, s) //constructor. Calls parent

constructor explicitly

Like Java, a C# derived class may not override a method by redefining it. The class

must use the keyword override in its method definition.


{

…

}

Protected Access

Like Java, in C#, you can use protected modifier to control access to fields, properties, and methods. You can implement protected variables in C# by using the

protected access modifier, as shown in the code sample below:

protected Point origin;

protected static int counter=0;

Instance vs. Class Level Access


47

Like Java, C# uses a static modifier to denote class level methods, fields, and

properties. Everything else is at an instance level. In the above code example, the counter is a class level variable.

protected static int counter=0;

Abstract Classes

The abstract classes are classes that cannot be instantiated. Java provides a syntax for an abstract class. The class Shape defined in the above C# code sample is an abstract class. The abstract classes requires that both Area and the method it

contains must be overridden in any derived classes.

abstract class Shape

{

public abstract double Area

{

get;

}

public abstract bool contains(Point p);

Interfaces

The Java and the C# interfaces are similar. In the sample code shown below, IThreeDShape defines an interface that is implemented by the Cube class.

interface IThreeDShape

{

double volume

{

...

class Cube : Shape, IThreeDShape

Polymorphism

The working of polymorphism is the same in both Java and C#. You can pass a C# derived class as a parameter to a method that expects a base class. Similarly, you can pass a class that implements a particular interface, as a parameter to the

method. The following sample code shows how to pass an object of the class Cube as a parameter, where the method expects an object of the class IThreeDShape.

static void printVolume(IThreeDShape tdShape)

{

Console.WriteLine(“The volume is ” + tdShape.volume);

}

…


48

Cube c = new Cube(4.0);

SecondProgram.printVolume(c);

Structs

C# structs are like classes. C# structs can access modifiers and have constructors, methods, and properties. While a struct is a value, a class is a reference.

struct Point

{

public double x;

public double y;


49

Object Lifecycle: Creation and Deletion of Objects

The memory management in both Java and C# are similar. Both Java and C#

performs automatic memory management. Instead of allocating memory, C# allows you to use the new operator to create objects and initialize them. When a code no longer accesses an object, the object becomes eligible for garbage collection. The

.NET CLR garbage collector in C# periodically frees up the memory for such objects. With C#, you don‟t have to track the free memory usage.

In rare circumstances, you may need to perform a cleanup at the time the object is destroyed. C# allows the use of destructors, but in practice this is rare.

Type Checking vs. Reflection

Java Reflection is a versatile feature that you can find both in C# and Java. You can

use reflection to:

Get information type from an existing object Dynamically create an instance of a type

Bind the type to an existing object, access its methods, and access its fields and properties.

The following table maps the dynamic type checking in Java with its corresponding C# reflection features.

Java Reflection Explanation C# Reflection

Class1 instanceOf BaseClass

Is Object a subclass or member?

type.IsSubclassOf(typeof(BaseClass))

object.getClass() Is Object a member

of

object.getType() or typeof

search from

Method[] methods =

c.getMethods();

Does the object implement the

method?

type.GetMethod(MethodName)

Does the class respond to the

method?

type.GetMethod(MethodName)

Method.invoke(..) Invoke a method type.InvokeMember(…)

Exception Handling

Exception handling is similar in both C# and Java. You use a use block to handle

exceptions. You can also use either catch specific exceptions or a catch-all statements. The syntax for exception handling is similar in Java and C#.


50

try

{

//block of code

}

//Most specific:

catch (ArgumentNullException e)

{

Console.WriteLine(“{0}First exception caught.”, e);

}

//Least specific

catch (Exception e)

{

Console.WriteLine(“{0}First exception caught.”, e);

}


51

A Comparison of Important Class Libraries

Strings

C# provides a comprehensive string class, which offers you all the features that you

associate with this class.

Java Feature

C# Notes

String String greeting = “Hello WP7!”;

Int length = greeting.Length;

Comparison String color = “pink”;

If (color == “red”)

System.Console.WriteLine(“Matchin

g colors!”);

string name = “Joe”;

if (string.compare(name, “Jack”)

> 0)

System.Console.WriteLine(name +

“ comes later”);

Strings are compared using ==. They are compared

lexicographically using compare.

Concatenation System.Console.WriteLine (greeting + " You rock!")

Strings can be concatenated

with the „+‟ operator. (This is called operator overloading.)

Splitting string rainbow = "Violet, Indigo,

Blue, Green, Yellow, Orange,

Red";

string[] rainbowColors =

rainbos.Split(',');

foreach (string color in

rainbowColors)

System.Console.WriteLine

(color);


52

Arrays

Arrays in C# are almost like arrays in Java.

Java Feature C# Notes

Arrays of primitive types such as int, float

int[] table;

table = new int[3];

string[] names = new string[3]

{"Peter", "Paul", "Mary"};

Array size is not a part of the array declaration.

Arrays are explicitly

initialized.

Multi-dim arrays

of primitive types

Int[,] mAray;

Int[][] jaggedArray;

string[][] singers = {new string[]

{"Peter", "Paul", "Mary"}, new

string[]{“Paul”,“Art”}};

C# supports jagged

arrays, or arrays of arrays, and they need not be rectangular.

Note: Arrays of strings, i.e. objects, work the

same way.

Mutable array of

objects

List<string> colors = new

List<string>; //list of strings

Colors.Add(“Red”);

Colors.Add(“Green”);

Colors.Insert(1,”White”);

String myColor = Colors[0]; //”Red”

Colors[colors.IndexOf(“Red”)] =

“Pink”; // replace Red with pink

You can use Lists as a

replacement for mutable arrays.

You may also use ArrayLists.

Dictionaries

C# provides a generic dictionary class that is similar to the HashTable functionality in Java. The generic dictionary class allows you to add, lookup, and remove objects

from the dictionary. Since the dictionary class uses Generics, it also utilizes strong typing.


53

Java C# Notes

Dictionary<string, int> d = new

Dictionary<string, int>();

d.Add("Honda", 124);

d.Add("Toyota", 95);

d.Add("Ford", 135);

// See if Dictionary contains

string

if (d.ContainsKey("Ford")) //

True

{

int v = d["Ford"];

Console.WriteLine(v);

}

You can use Dictionary as

a replacement for NSMutableDictionary.


54

The New features of C#

This section covers the following:

Generics Operator Overloading

Delegates Events Generics

Generics

Generics introduce the notion of type parameters that make it possible to design classes that are type safe, even though the actual type is deferred till the object‟s instantiation. For example, the following code shows how to define a generic stack:

Stack<int> intStack = new Stack<int>(); // intStack is a stack

of int

intStack.Push(1); // OK

intStack.Push(2); // OK

int number = intStack.Pop(); // this is a type safe

assignment

Stack<string> strStack = new Stack<string>(); //the type of strStack

is different from type of intStack

strStack.Push("green"); // OK

strStack.Push(23);

The Stack<T> uses T as a type parameter, thus allowing you to instantiate a stack of any type. For example: Stack<int> or Stack<string>. You can use them in a type safe manner. The use of generics is like generics in Java.


55

Operator Overloading

Operator Overloading allows you to define the implementation of user-defined

operators for user-defined classes. Consider the following example of a complex number struct. Operator Overloading allows you to define a + operation by using a natural syntax.

public struct Complex

{

public int real;

public int imaginary;

// Declare which operator to overload (+), define how it is

computed

public static Complex operator +(Complex c1, Complex c2)

{

return new Complex(c1.real + c2.real, c1.imaginary +

c2.imaginary);

}

…

Complex c1 = new Complex(3.0, 4.0);

Complex c2 = new Complex(4.0, 5.0);

Complex cSum = c1 + c2;


56

Delegates

The functionality of delegates in C# is like the function pointers in C. In this design

pattern, a class delegates another class even if which is not known at compile time.

using System;

namespace DelegateExample

{

public class ConsoleLogger

{

public static void WriteString(string s)

{

Console.WriteLine("Writing to console log: {0}", s);

}

}

public class FileLogger

{

public static void LogString(string s)

{

Console.WriteLine("Logging to file log: {0}", s);

}

}

public class DelegatesTest

{

public delegate void StringDelegate(string s);

public static void Main()

{

StringDelegate Writer, Logger; // define twp

StringDelegate objects

Writer = new StringDelegate(ConsoleLogger.WriteString); //

Create delegates with appropriate methods

Logger = new StringDelegate(FileLogger.LogString);

Writer("Warning message 1\n"); // Send to

Console Writer delegate method

Logger("Warning message 2\n"); // Send to File

Logger delegate method

StringDelegate MultiLogger; // to act as

the multicast delegate

MultiLogger = Writer + Logger; // combine the

two delegates,

MultiLogger("Warning message 3"); // This should

get sent to both delegates

}

}

}

In the above code example, StringDelegate is defined as a function that takes a string as a parameter and returns void. Writer, logger, and multiLogger are constructed by passing methods that have the same signature as the

StringDelegate declaration.

Calling Writer invokes the writeString method of ConsoleLogger to print the

message to the console. Calling Logger invokes the logString method of FileLogger


57

to log the message to the file. Delegates achieve indirection while providing type

safety. Delegates may be concatenated as shown by MultiLogger, which logs the message to both loggers.

Events

Events in C# are useful in the pub-sub (publisher and subscriber) design pattern.

Events are powerful design patterns that are used for asynchronous programming. An object can publish a set of events that a subscriber can subscribe. When a

publisher raises an event, all subscribers are notified. The publisher raises the event, but does not know who listens to it. The events are built by using delegates.

using System;

namespace DelegateExample

{

public class ConsoleLogger

{

public void WriteString(string s)

{

Console.WriteLine("Writing to console log: {0}", s);

}

}

public class FileLogger

{

public void LogString(string s)

{

Console.WriteLine("Logging to file log: {0}", s);

}

}

public class DelegatesTest

{

public delegate void LogEventHandler(string s); //

definition of the delegate.

public static event LogEventHandler logEvent; //

the signature of the event.

public static void Main()

{

ConsoleLogger cl = new ConsoleLogger(); //

create the first subscriber

FileLogger fl = new FileLogger(); //

the second subscribe

logEvent += new LogEventHandler(cl.WriteString); //

subscribe the event and hook up the

logEvent += new LogEventHandler(fl.LogString); //

event handlers

logEvent("A new event"); //

raise event which will invoke handlers

Console.ReadLine();

}

}

}


58

Comparing API Documentation Tools

JDK contains an API documentation generation tool called Javadoc. Javadoc

automatically generates documentation from the comments that are added to the java source code file.

There are a variety of document generation tools that are available for .NET:

NDoc Sandcastle

Doxygen Doc-O-Matic

NDoc

NDoc is a code documentation generator for Common Language Infrastructure.

NDoc uses pluggable documenters to generate documentation in several formats, including:

MSDN style HTML Help format (.chm) Visual Studio .NET Help format (HTML Help 2)

MSDN online style web pages

Using NDoc

To use NDocs to generate documentation, do the following:

1. Open your Windows Phone 7 project.

2. Select the class library for which you want to create documentation.

3. Right-click the class library, and click Properties.


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4. In the left pane, click Build.


60

5. Select the XML documentation file check box.

6. Enter the file name.

Note: NDoc uses this file for creating documentation.

Build your class library, the documentation file is saved in the Debug or Release

folder depending on your build configuration. You can see the documentation file in the XML format.

You can use NDoc‟s help to get a fair idea of documenting your class library more effectively.

Generating Better Documentation

To generate better documentation, follow these tips:

Write elaborate code comments for your code. Elaborate comments make your documentation descriptive.

Each Public type and the Public and Protected members of the Public types

should have an item describing the members. The VS.NET C# code editor has a feature that makes it easy to create the

basic code comments for each type and member. Consider the following code snippet:

public class MyClass() {

public MyClass(string s ) {}

}

Place your cursor just above the MyClass constructor, and press the '/' character

three times. Visual Studio.NET creates the skeleton of a code comment block for that member:

public class MyClass() {

///<summary>

///

///</summary>

///<param name=”s”></param>

Public MyClass(string s) {}

}

You can use this method to any type or member that have code comment tags.

NDoc supports a large number of documentation tags. You can use the tags to

meet your requirements.


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In a code comment block, when you press the '<' key to start a new tag, Visual

Studio.NET displays an Intellisense selector. This selector shows a list of code comment tags. This list does not display the additional tags that NDoc supports.

You must add the additional tags manually.

Using the NDoc GUI Utility

To use the NDoc GUI Utility, do the following:

1. Double-click NDocGui.exe, to start NDocGUI.

2. Click Project, then click New.

3. In the section Select and Configure Documenter, select documentation type from the Documentation Type list.

4. Under Select and Configure Documenter, specify the parameters, such as Copyright text and Output directory.

Note: The most important settings are in the Visibility section. Here you can configure the elements that you want to document, such as private variables, protected variables, and Namespaces without summaries.

5. Click Add.

6. In the Add Assembly Filename and XML Documentation Filename

dialog, select the required EXE or DLL. NDoc processes the XML documentation file based on your selection.

After building your project, find the compiled documentation for your class library in

the output directory that is specified in the output message.

NDocs vs. Javadoc

A Javadoc tool can be run on Windows, Mac OS, Unix, and BSD. However,

NDoc can run only on Windows. A Javadoc tool is for generating documents from java source files. The tool

therefore accepts text as an input. NDoc accepts only binary files as an

input. A Javadoc tool generates documents in an HTML format by default. You need

a third-party tool called Doclet to generate an output in other formats, such as CHM, RTF, PDF, and postscript. NDoc can generate documents in various

formats, such as MSDN, Linear HTML, and JavaDoc.

Summary


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In this chapter, we looked at C# programming from the perspective of a Java

developer. C# is a strongly typed, object-oriented programming language that uses static binding. Several C# concepts are similar to the Java concepts. The knowledge

of Java and object oriented programming will help you to master C# quickly. We also looked at NDocs, which is the API documentation tool for Windows Phone 7.

Related Resources

To go deeper into C# and Java, visit:

http://www.25hoursaday.com/CsharpVsJava.html

To go deeper into NDocs, visit:

http://ndoc.sourceforge.net/

http://shfb.codeplex.com/ – Sandcastle Summary

http://www.25hoursaday.com/CsharpVsJava.html

http://ndoc.sourceforge.net/

http://shfb.codeplex.com/


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Chapter 5: A Comparison of

Application Life Cycles in Windows

Phone 7 and Android

The Windows Phone 7 (WP7) execution model improves user experience by cutting down on response time and offering seamless navigation among applications. To

achieve this, WP7 prioritizes the foreground application and tombstones other open applications. Android on the other hand, saves all the application states and

displays only the foreground application.

Android suspends an open application when a user starts another application. The suspended application remains alive in the phone memory. WP7 activates and

deactivates applications dynamically to enable seamless navigation by limiting the phone to run one application at a time.

The WP7 execution model provides users with a consistent navigation experience between applications.

In Android, users open applications using the launcher screen. On the launcher

screen, all the applications are listed as icons. In WP7, users navigate forward by launching applications from the installed Applications List or from a tile on the

Start screen.

In WP7, users can use the Back button on the phone to navigate backwards to a page in a running application. With this Back button, users can also navigate

through a stack of previously running applications. This WP7 functionality is similar to Android‟s backward navigation. All Android devices have the Back button on the

phone. A user can navigate to previous screens of applications until he reaches the home screen of phone.

The Android applications consist of various components, such as Activity, Services,

ContentProvider, and Broadcast receivers. These components are not available in WP7 except for an Activity which can be mapped to a Page in WP7.

Multitasking in Android and Windows Phone 7

Android supports multitasking and provides seamless navigation between applications. WP7 achieves seamless navigation using application tombstoning.

Android puts applications in the background using the Service component. The Service component runs in the background even if your application is not in foreground until the application‟s task finishes or stopService is called.

The upcoming version of WP7 will support multitasking. The WP7 navigation model allows natural navigation, similar to a browser‟s Back button. The last accessed


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application state is preserved as a user navigates across applications using the Back

button on the phone.

Tombstoning of Applications in Windows Phone 7

Tombstoning is a process by which WP7 deactivates an application when a user

navigates away from this application. WP7 keeps a record of the tombstoned application and stores the latest data accessed by this application. If the user returns to a tombstoned application, WP7 reactivates this application. The user can

access the reactivated application by using a phone‟s Back button.

Consider the following example. A user is composing a blog with WordPress. He

pressed the Start button to go to the Start screen. WP 7 deactivated the WordPress application. The user then accessed Facebook. While in Facebook, the user pressed the Back button. The Start screen appeared. When the user pressed the Back

button again, WordPress appeared exactly in the same way as she had viewed it the last time.

The following table describes the user events and compares the corresponding behavior in Android and Windows Phone 7.

User Action or Event Android Behavior Windows Phone 7 Behavior

An incoming phone call or SMS

Running application is moved to the background

but is still in the memory

Running application is deactivated

User presses the Home

button on the phone

Running application is

moved to the background, current activity will be paused but the application

is still in memory

Running application is

deactivated

User starts another

application from the multitasking menu

Background application is

moved to foreground with the earlier saved state

The upcoming version of

WP7 will support multitasking

User navigates between applications using the

Back button on the phone

No navigation occurs when Back button is

pressed when user is at the home screen of the phone.

Deactivated or tombstoned application is

activated to the earlier saved state

Life Cycle of a Windows Phone 7 Application


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There is no similarity between the Android life-cycle stages with the WP7‟s Page

stage. Activity is the only component that can be mapped with a Page in WP7.

The following events take place during the life cycle of a WP7 application:

Launching

An application is launched when it is started by all other means except when the

user navigates to it using the Back button.

Whenever a user opens an application, WP7 creates a new instance of the

application. In Android, when an application launches a new process a new instance of Dalvik VM is allocated to the application. The application runs within that process. Each application runs in its own process and VM instance.

Do not store the state data when the launching event is raised. The launching event is raised even before application is visible to the user. Storing data at this stage

may increase the startup time of the application.

Running

After launching, the application goes into the running stage. In this stage, the application manages its own state as the user navigates through the different pages

of the application.

In the running stage, settings and the persisted data are saved. This reduces the data that you need to save when the application‟s stage changes. However, the

decision to save data in this stage is optional. If the size of the persisted data is not large, you need not save the data.

Closing

Your application comes across this event when the user presses the Back button on

the phone, when he is in the application‟s first page.

In the handler for this event, you can save data to an isolated storage. This action

is similar to handling the Destroyed() method in Android.

In Android, you cannot close an application after launching. Each activity in the application can be finished but the application process remains in the memory.

Deactivating

WP7 deactivates your application in the following scenarios:

A user opens another application A user locks the phone screen

An event accesses the Launcher or Chooser APIs A user presses the Windows button to open the Start screen on the phone

A user presses the Search button on the phone

In the handler for this event, you must save the transient data to the state property and the persistent data to the isolated storage. This helps maintaining consistent

user experience after the user activates the application again.


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Android suspends a current application‟s activity when a new application comes to

the foreground.

Activating

WP7 raises this event:

If a user returns to a deactivated application using the Back button on the

phone If a user returns to a tombstoned application, which was deactivated by

Launcher or Chooser

This event is similar to resuming an Activity in Android. However, WP7 creates a new instance of the application when a user starts the application from:

A phone‟s Applications List An application‟s tile on the Start screen

A toast notification

In the handler for this event, you restore all the transient data of the application. The transient data restores the application to the state before the application was

deactivated.

You must avoid accessing the isolated storage or network resources in this event

handler. When you access an isolated storage or network resources, an application's launch time may increase.

Role of Handlers in an Application‟s Life Cycle

In WP7, your applications transition between the active and inactive states. You can

implement handlers for an application‟s life-cycle events to save and restore application states.

A WP7 application‟s life cycle offers users consistency while working with applications. The users feel that the application is running in the background when it is not visible to him.

In Android, you save application state when an activity is paused. You can use the method onSaveInstanceState to access the event, and use the method

onRestoreInstanceState to restore the event to previous state.


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Figure: Windows Phone 7 Application Life Cycle


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Comparing Life-cycle Methods

As mentioned in the earlier sections, a Page in WP7 is similar to an Activity in

Android. We can compare the Android lifecycle method with WP7‟s state-change events and Page methods.

Windows Phone 7

Stage

Windows Phone 7 Application Events

Windows Phone 7 Page Methods

Android Methods

Launching Application_Launching InitializeComponent() onCreate()

Running onStart(), onResume()

Deactivated Application_Deactivated NavigatedFrom onStop(), onPause()

Activation Application_Activated NavigatedTo onResume()

Closing Event Application_Closing onDestroy()

In Android, you can use the onCreate() method to initialize the variables, such as

the view components, the database connection, and a GPS provider. In WP7, you can use the InitializeComponent() method in the constructor of the Page class to

initialize variables. You also need to get the application_launching event to define the global variables in InitializeComponent() method.

In Android, if a user launches a new application, the current application activity

calls the onPause and onStop methods. In this scenario, you can commit the application data to the database. But in WP7, if a user launches a new application,

the current application is deactivated. At the time of deactivation, WP7 calls the Application_Deactivated function. You need to save the application‟s state-data in the Application_Deactivated function.

In Android, a user can see the running application on a phone by keeping the Home button on the phone pressed for some time. The user can also resume a running

application from the running applications list. In this scenario, Android calls the application activities on the Start and onResume lifecycle methods. With these methods, you can restore the data from a previous state. In WP7, when a user

starts a tombstoned application, the Application_activated function is called. You can restore the data from the previous state of the application to this function.

In Android, when one Activity replaces another, the current Activity calls the onPause and onStop methods. This behavior is similar to the Page to Page navigation in WP7. In WP7, While moving from one page to another, the current

page raises the NavigatedFrom() event and the new page raises the NavigatedTo() event.


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Tombstoning and Windows Phone 7 Life Cycle

Consider a simple example that illustrates the WP7 application life cycle stage

transitions and tombstoning. Here is a single page example application called Shopping List. In this application, the user can add items to a shopping list. When

the user leaves the application, the shopping list is saved automatically.

Saving the Application State Data

In Android, you can save application state data in a number of different ways. For example, using SharedPreferences, using files in the internal storage/external

storage, or using SQLLite.

To save the persistent state data of an application on WP7 you can use IsolatedStorage. IsolatedStorage is a safe storage space that is accessible only to

that application to which the space is allocated. One application cannot affect another application‟s data. To save the stage data, you need to get the

IsolatedStore for the application. After that, create a file in IsolatedStorage, to save the persistent state. In our example of the Shopping List application, you can serialize the list and save it to the file.

public static void SaveShoppingList(ShoppingListInfo shoppingListInfo, string

fileName)

{

//Get the isolatedStore for this application

using (IsolatedStorageFile isf =

IsolatedStorageFile.GetUserStoreForApplication())

{

// create a new file

using (IsolatedStorageFileStream fs = isf.CreateFile(fileName))

{

//and serialize data and save it

XmlSerializer xmlSer = new

XmlSerializer(typeof(ShoppingListInfo));

xmlSer.Serialize(fs, shoppingListInfo);

}

}

}

WP7 provides another class called PhoneApplicationService.State to save the transient stage data.

Terminating Applications


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When the user uses the back button to leave an open application, WP7 terminates

the application. Depending on the nature of your application, you may need to save certain data when WP7 terminate your application.

In the example of the Shopping List application, you can save the application data without confirmation from the user. This ensures that the shopping list is intact, when the user get opens the application next time. In this example, you are not

saving any item that the user is typing in the Item text box. You can use the helper method to save the shopping list. Your application can perform such cleanup

and state saving operations in response to the Application_Closing event instead of OnBackKeyPress.

protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs

e)

{

base.OnBackKeyPress(e);

//do not save what is in the item, i.e. it is transient

txtItem.Text = "";

//preserve data in persistent store

Utils.SaveShoppingList((App.Current.RootVisual as

PhoneApplicationFrame).DataContext as ShoppingListInfo,

"ShoppingListInfo.dat");

}

}

Application Launching

When the user starts an application from the Start screen, the application receives

the Application_Launching event.

During launch, you can examine whether any persistent data is available. In the

Shopping List application, if you find the persistent data, load the data in the txtList text box to launch the shopping list. You can first get the IsolatedStore for the application. Using the IsolatedStore, check if the ShoppingListInfo.dat file exists. If

the DAT file is available, you can de-serialize the existing data and reload the ShoppingListInfo.

You can make the fields in Shopping List application databound using the last line in this code snippet. Now, if you run the application, you find that the shopping list is preserved when the application is closed and presented when you launch the

application again.

// Code to execute when the application is launching (eg, from Start)

// This code will not execute when the application is reactivated

private void Application_Launching(object sender, LaunchingEventArgs e)

{

//Trace the event for debug purposes

Utils.Trace("Application Launching");

//Create new data object variable

ShoppingListInfo shoppingListInfo = null;


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//Try to load previously saved data from IsolatedStorage

using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())

{

//Check if file exits

if (isf.FileExists("ShoppingListInfo.dat"))

{

using (IsolatedStorageFileStream fs = isf.OpenFile("ShoppingListInfo.dat",

System.IO.FileMode.Open))

{

//Read the file contents and try to deserialize it back to data object

XmlSerializer ser = new XmlSerializer(typeof(ShoppingListInfo));

object obj = ser.Deserialize(fs);

//If successfully deserialized, initialize data object variable with it

if (null != obj && obj is ShoppingListInfo)

shoppingListInfo = obj as ShoppingListInfo;

else

shoppingListInfo = new ShoppingListInfo();

}

}

else

//If previous data not found, create new instance

shoppingListInfo = new ShoppingListInfo();

}

//Set data variable (either recovered or new) as a DataContext for all the pages of

the application

RootFrame.DataContext = shoppingListInfo;

}

Deactivating Applications

This event occurs when a user press the Start button while running an application.

Android suspends the current application‟s activity whenever a new application comes to foreground. In WP7, the application receives the Application_Deactivated

event.


72

In response to this event, you can save the entire application state. In the example

of the Shopping List application, you need to save the shopping list as well as the text entered in the Item text box.

You can save the transient application state by using the PhoneApplicationService.State object.

// Code to execute when the application is deactivated (sent to background)

// This code will not execute when the application is closing

private void Application_Deactivated(object sender,

DeactivatedEventArgs e)

{


Utils.Trace("Application Deactivated");

//Add current data object to Application state

PhoneApplicationService.Current.State.Add("UnsavedShoppingListInfo",

RootFrame.DataContext as ShoppingListInfo);

}

Activating Applications

If a user returns to a deactivated application using the Back button on the phone, WP7 raises the Application_Activated event.

In response to this event, you can load the data from the PhoneApplicationService.State object. If you find the necessary data for launching the application, you can populate the UI elements using that data. If you do not

find any saved data, keep the UI fields blank.

To test the Shopping List application for this code snippet, press the Home button

to leave the application and navigate back to the application using the Back button. You will find that both the shopping item in the text box and the shopping list are preserved.

// Code to execute when the application is activated (brought to foreground)

// This code will not execute when the application is first launched

private void Application_Activated(object sender, ActivatedEventArgs e)

{


Utils.Trace("Application Activated");

//Create new data object variable

ShoppingListInfo shoppingListInfo = null;

//Try to locate previous data in transient state of the

application

if

(PhoneApplicationService.Current.State.ContainsKey("UnsavedShoppingListInfo")

)

{


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//If found, initialize the data variable and remove in from

application's state

shoppingListInfo =

PhoneApplicationService.Current.State["UnsavedShoppingListInfo"] as

ShoppingListInfo;

PhoneApplicationService.Current.State.Remove("UnsavedShoppingListInfo");

}

//If found set it as a DataContext for all the pages of the

application

//An application is not guaranteed to be activated after it has

been tombstoned,

//thus if not found create new data object

if (null != shoppingListInfo)

RootFrame.DataContext = shoppingListInfo;

else

RootFrame.DataContext = new ShoppingListInfo();

}


74

Summary

In this chapter we had a look at the different stages of application life cycle in

Android and Windows Phone 7. We also compared methods for saving application state data in Android and Windows Phone 7.

Related Resources

To know more about the execution model for Windows Phone 7, visit:

Execution Model Overview for Windows Phone Execution Model Best Practices for Windows Phone

How to: Preserve and Restore Page State for Windows Phone How to: Preserve and Restore Application State for Windows Phone

Android Application Life-cycle Diagram

http://msdn.microsoft.com/en-us/library/ff817008(v=vs.92).aspx




http://developer.android.com/images/activity_lifecycle.png


75

Chapter 6: Storing Data and

Preferences

Windows Phone 7 (WP7) features a very comprehensive system of managing data for your application and across all applications on the phone. This section compares

the data handling features of WP7 and Android.

Isolated Storage in Windows Phone 7

With WP7, you can store data in the device file system of your application. This type of data storage is called IsolatedStorage.

The following diagram shows the folder structure for a storage application:


76

Comparing the Data Storage Methods in Windows Phone 7 and Android

Storage Methods

Windows Phone 7 Android

Storage

You can store the application

data in IsolatedStorage

You can store the application

data in the phone‟s internal storage, which is private to your application

Windows Phone 7‟s isolated storage model allows the

managed applications to create and maintain the local

database.

InternalStorage enables applications to create and

maintain local data.

Security Windows Phone 7 does not

allow the application to make the file system calls outside the isolated storage area or

outside of the operating system area. This design gives

a sandbox effect to the application. The advantage of this design is that the

application cannot access the data storage area of other

applications.

Neither the user nor other

applications can access the data stored in the internal storage. The internal storage

area is private to the respective application.

Security Windows Phone 7 restricts all

Input and Output (I/O) operations to isolated storage and prevents the I/O

operations from accessing the operating system files. This

Windows Phone 7 feature prevents unauthorized access and data corruption.

Android prevents unauthorized

data access by restricting I/O operations of internal storage to the same application.

However, you have an option to make this data public by

writing data to external storage.

Installation When you update an application after it is available

in the market, Windows Phone 7 does not modify the isolated

storage folder. You need to ensure that the data is migrated or transformed

appropriately to work with the new version of the application

Android does not delete the application data after

uninstalling or reinstalling. While updating the applications

that are already in the market, you need to ensure that the data is updated to maintain

compatibility with the updated version of the application.


77

Uninstallation When an application is uninstalled, Windows Phone 7 deletes the uninstalled,

Windows Phone 7 deletes the data root, the isolated storage

folder, and all the data within the store.

Android deletes only the internal storage of an application when the

application is uninstalled.

Memory Space Windows Phone 7 does not restrict applications from using the memory space.

Adequate memory is provided to each application depending

on the requirement.

The internal storage limit of an Android application is dependent on the availability

of memory. Your application must use the memory

carefully.

Settings Windows Phone 7 allows you

to store the settings for the application in the IsolatedStorageSettings area.

You can store key and value pairs of data in this memory

space.

Android allows you to store an

application‟s settings in the SharedPreference memory space. You can store the

primitive data types in key/value pairs.

To know more about the comparison between the data storage methods, visit:

IsolatedStorage for Windows Phone Windows Phone 7 Series Developer General FAQ


•%09http:/social.msdn.microsoft.com/Forums/en-US/windowsphone7series/thread/2892a6f0-ab26-48d6-b63c-e38f62eda3b3


78

Use Cases

Storing the Configuration Settings and Data

Many applications need to store application settings and data, such as user name,

password, and language preference, and last login time stamp. The nature of such data depends on the nature of the application.

In Android, you can store such application settings and data by using the

SharedPreferences class. The SharedPreferences class stores the key value pair of primitive data types. In WP7, you can save this data by using the

IsolatedStorageSettings.ApplicationSettings property.

IsolatedStorage stores objects by using the IsolatedStorageSettings.ApplicationSettings property. This is the most convenient

way to store simple data. You just need to add your data to the Settings store by using the following code:

IsolatedStorageSettings.ApplicationSettings.Add(“some_property”, value); IsolatedStorageSettings.ApplicationSettings.Save();

The value object is serialized automatically to a disk when you call the Save()

method. You can read back data by using the following code:

List<string> mydata =

(List<string>)IsolatedStorageSettings.ApplicationSettings["some_property"];

Serializing Objects to XML

You may need to serialize an entire object to the file system to save the state of object or to save the memory. In Java, you can serialize objects by using ObjectOutputStream. In WP7, you can serialize objects by using the StreamWriter

class.

You can store objects as XML by using the following code. This code serializes a list

of strings to the xml format and saves this format in IsolatedStorage:


79

using(IsolatedStorageFile storage =

IsolatedStorageFile.GetUserStoreForApplication()){

using(IsolatedStorageFileStream fs = storage.CreateFile(“myfile.wp”)){

using(StreamWriter writer = new StreamWriter(fs)){

XmlSerializer serializer = new XmlSerializer(typeof(List<string>));

serializer.Serialize(writer, myStringList);

}

}

}

After storing the data in the XML format, you can use LINQ to XML to utilize the

data later. You can use this method to store any structured data on a disk.

Note: For details about LINQ to XML, see Chapter 8.

To read back the file, use the following code:

using(IsolatedStorageFile storage =

IsolatedStorageFile.GetUserStoreForApplication()){

using(IsolatedStorageFileStream fs = storage.OpenFile(“myfile.wp”,

FileMode.Open)){

XDocument doc = XDocument.Load(fs);

XmlSerializer serializer = new XmlSerializer(typeof(List<string>));

List<string> myData =

(List<string>)serializer.Deserialize(doc.CreateReader());

}

}

Managing the IsolatedStorage Space

The Windows Phone 7 applications do not have an imposed quota size because the requirements for each application‟s scenario are different. Also, limiting the disk

size on a per application basis can increase the response time and dilute user experience. Therefore, ensure that your application stores only the necessary data

for a subsequent launching of the application.

The storage space in mobile phones is limited. Windows Phone 7 displays a notification to the user when only 10% of the storage-space remains. The user

needs to delete the existing data to create the necessary storage space. From a user‟s point of view, this is not a favorable option.

The Best Practices for Managing the IsolatedStorage Space

The following best practices help you to efficiently manage the data storage-space

in Windows Phone 7:

Temporary data and files

If your application stores any temporary data in IsolatedStorage, delete the temporary data if the data is no longer required. For example, delete the earlier

version of the data when the updated version is available. You can implement periodic deletion of data by creating a temporary cache folder for the data and by

clearing the cache from time to time.


80

User generated data

The user generated data can be in the form of photos from the camera, or notes

and documents.

If your application allows a user to create data, offer the user the delete option. For example, users should be able to take photos and delete those

that they do not want. Increase the performance of an application by reducing the application‟s

footprint. You can use techniques, such as: o Synchronizing or archiving data to the cloud o Keeping only the relevant data

Application Data

Examples of application data include:

A list of stores or shops that are managed by a shopping list application Words in a dictionary

Note: If your application takes data from the cloud and stores it locally, recycle the data based on your priorities.

Why Windows Phone 7 Does Not Use External Storage

You can save files to a shared external storage in an Android compatible device. The shared external storage can also include the internal non-removable storage. Android allows you to access and modify the files that are saved to the external

storage by connecting to a computer. In this type of connection, the files might get deleted or corrupted if the connection gets disconnected during the data transfer.

You cannot make the file system calls outside the WP7 application‟s own external space. This provides the application with a safe-sandbox, and prevents the other applications from inadvertently affecting the application's data.

Library Recommendation for Supporting SQLite in Windows Phone 7

Android features SQLite version 3.4.0. Android also provides the API for managing

the SQLite database. This API provides the methods to create, delete, run SQL commands, and perform the other common database management tasks. An

Android application can create a database to store and manage the structured data on phone. The application can also share the same database with other applications by using a ContentProvider.

WP7 does not feature SQLite. You can use a third-party library to get that functionality in WP7.

To know more about incorporating SQLite in WP7, visit:

http://sqlitewindowsphone.codeplex.com/

http://wp7sqlite.codeplex.com/

http://sqlitewindowsphone.codeplex.com/

http://wp7sqlite.codeplex.com/


81

Managing Content across Applications

In Android, ContentProviders store and retrieve data and make the data accessible

to all applications. In Android, you can share data only through ContentProviders. However, Android does not provide a common data storage area that all Android

applications can access.

Android provides you two ways to make the application data public by using ContentProviders:

You can create your own ContentProvider. This is the ContentProvider subclass.

You can add the data to an existing provider. For this, you need a ContentProvider that controls similar data and the permission to write to it.

To know more about ContentProviders, visit:

http://developer.android.com/guide/topics/providers/content-providers.html

The WP7 execution model isolates every application in its own sandbox for both

running the application and for storing data. Applications cannot access information from the common information stores, such as the contacts list. Applications also cannot directly invoke other applications, such as the phone or messaging

applications. To enable applications to perform these common tasks, WP7 offers a set of APIs called Launchers and Choosers. They allow applications to indirectly

access the various features of a phone.

Launchers and Choosers

The Launcher and Chooser APIs call the distinct built-in applications that replace the currently running application.

Android has functionality similar to Launchers and Choosers. In Android, you use the Intent filter and the Intent API to launch any built-in or installed applications to return the data you need or to perform a task.

To know more about the Intent filters, visit:

http://developer.android.com/guide/topics/intents/intents-filters.html

Launchers

A Launcher is an API that starts built-in applications in WP7. Your application can complete the tasks through these built-in applications for which no data is returned back to your application. Let‟s take the example of PhoneCallTask. Your application

can provide the PhoneCallTask Launcher with a phone number and display a name to access the phone. When the phone displays the built-in application, the user can

choose whether to initiate the call by using the supplied parameters. When the user closes the built-in application, your application is activated again. But the built-in application does not return any data that result from the user‟s actions.

http://developer.android.com/reference/android/content/ContentProvider.html

http://developer.android.com/guide/topics/providers/content-providers.html

http://developer.android.com/guide/topics/intents/intents-filters.html


82

Choosers

A Chooser is an API that launches the built-in applications in WP7. Your application can complete various tasks by using these built-in applications for which your

application needs data in return.

For example, consider the PhotoChooserTask. Your application can use the PhotoChooserTask Chooser to show the built-in Photo Chooser application. The user

can either select a photo or close the Photo Chooser. Now, WP7 activates your application and supplies the result of the Chooser. The result indicates whether the

user completes the task. If the user completes the task, the result includes an I/O stream that contains the image data of the photo.

After the Photo Chooser application is launched, the user can press the Start button

on the phone and select another application. In this case, WP7 does not reactivate your application and does not return the results generated by Chooser. Your

application should handle this ambiguity properly.

Comparing Intent API with Launchers and Choosers API

This table compares the Intent API of Android with Launchers and Choosers APIs of

WP7. This section compares the mechanism of handling cross application data and performing tasks based on data I/O in WP7 and Android platforms.

Function Android Windows Phone 7

Camera Intent intent = new

Intent("android.media.action.

IMAGE_CAPTURE");

startActivityForResult(intent,

0);

CameraCaptureTask

cameraCaptureTask = new

CameraCaptureTask();

cameraCaptureTask.Completed

+= new

EventHandler<PhotoResult>

(cameraCaptureTask_Complete

d);

cameraCaptureTask.Show();

Email

chooser and composer

Intent emailIntent = new

Intent(android.content.Intent.ACT

ION_SEND);

emailIntent

.setType("plain/text");

emailIntent

.putExtra(android.content.Intent.

EXTRA_EMAIL, new

String[]{"[email protected]"}

EmailAddressChooserTask,

EmailComposeTask,

EmailResult,

SaveEmailAddressTask

EmailComposeTask

emailComposeTask = new

EmailComposeTask();

emailComposeTask.To =

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.cameracapturetask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.emailaddresschoosertask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.emailcomposetask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.emailresult%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.saveemailaddresstask%28VS.92%29.aspx


83


);

emailIntent


EXTRA_SUBJECT, mySubject);

emailIntent


EXTRA_TEXT, myBodyText);

startActivity(emailintent);

"[email protected]";

emailComposeTask.Body =

"Email message body";

emailComposeTask.Cc =

"[email protected]";

emailComposeTask.Subject =

"Email subject";

emailComposeTask.Show();

Market Intent market_intent = new Intent

(Intent.ACTION_VIEW,

Uri.parse("market://search?

q=pname:com.google.somepackage")

)

startActivity(market_intet);

MarketplaceHubTask,

MarketplaceDetailTask,

MarketplaceReviewTask,

MarketplaceSearchTask

MarketplaceSearchTask

marketplaceSearchTask = new

MarketplaceSearchTask();

marketplaceSearchTask.

SearchTerms =

"accelerometer xna";

marketplaceSearchTask.Show(

);

Media player Intent i = new

Intent(Intent.ACTION_VIEW);

Uri u = Uri.parse(xpath);

i.setData(u);

startActivity(i);

MediaPlayerLauncher

MediaPlayerLauncher

mediaPlayerLauncher = new

MediaPlayerLauncher();

mediaPlayerLauncher.Media =

new Uri("MyVideo.wmv",

UriKind.Relative);

mediaPlayerLauncher.Location

= MediaLocationType.Data;

mediaPlayerLauncher.Controls

=

MediaPlaybackControls.Pause

|

MediaPlaybackControls.Stop;

mediaPlayerLauncher.Show();

Phone call String url = "tel:3334444";

Intent call_intent = new Intent

PhoneCallTask

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.marketplacehubtask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.marketplacedetailtask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.marketplacereviewtask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.marketplacesearchtask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.mediaplayerlauncher%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.phonecalltask%28VS.92%29.aspx


84


(Intent.ACTION_CALL,

Uri.parse(url));

startActivity(call_intent);

PhoneCallTask phoneCallTask

= new PhoneCallTask();

phoneCallTask.PhoneNumber =

number;

phoneCallTask.DisplayName =

name;

phoneCallTask.Show();

Address book In Android you can access

anything that is stored in the

address book. For example, name,

address, and number.

Intent intent = new

Intent(Intent.ACTION_PICK,

People.CONTENT_URI);

startActivityForResult(intent,

1);

PhoneNumberChooserTask,

PhoneNumberResult,

SavePhoneNumberTask

phoneNumberChooserTask = new

PhoneNumberChooserTask();

phoneNumberChooser

Task.Completed += new

EventHandler<PhoneNumberResu

lt>

(phoneNumberChooserTask_Comp

leted);

phoneNumberChooserTask

.show();

Photo chooser

Intent i = new

Intent(Intent.ACTION_GET_CONTENT)

;

i.setType("image/*");

startActivityForResult(i,4);

PhotoChooserTask,

PhotoResult

photoChooserTask = new

PhotoChooserTask();

photoChooserTask.Completed

+= new

EventHandler<PhotoResult>

(photoChooserTask_Completed)

;

photoChooserTask.Show();

Web search Intent search = new

Intent(Intent.ACTION_WEB_SEARCH);

search.putExtra(SearchManager.QUE

SearchTask

Task searchTask = new

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.phonenumberchoosertask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.phonenumberresult%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.savephonenumbertask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.photochoosertask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.photoresult%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.searchtask%28VS.92%29.aspx


85


RY, "android");

startActivity(search);

SearchTask();

searchTask.SearchQuery =

txtInput.Text;

searchTask.Show();}

SMS Intent sendIntent = new

Intent(Intent.ACTION_VIEW);

sendIntent.putExtra("sms_body",

"The SMS text");

sendIntent.setType("vnd.android-

dir/mms-sms");

startActivity(sendIntent);

SmsComposeTask

SmsMessage SMSComposer = new

SmsMessage("123456789","This

is a sample sms");

MessagingApplication.

DisplayComposeForm(SMSCompos

er);

Web browser

chooser

Intent myIntent = new

Intent(Intent.VIEW_ACTION,

Uri.parse("http://www.google.com"

));

startActivity(i);

WebBrowserTask

WebBrowserTask wb= new

WebBrowserTask();

wb.URL =

"http://www.google.com";

wb.Show();

Summary

In this chapter we compared data storage guidelines for Windows Phone 7 and Android. We also looked at the storage APIs in Windows Phone 7 and Android.

Related Resources

To learn more about the topics covered in this blog, visit:

Launchers and Choosers Overview for Windows Phone Launchers and Choosers

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.smscomposetask%28VS.92%29.aspx

http://www.google.com/

http://msdn.microsoft.com/en-us/library/microsoft.phone.tasks.webbrowsertask%28VS.92%29.aspx

http://msdn.microsoft.com/en-us/library/ff769542(VS.92).aspx

http://msdn.microsoft.com/en-us/gg266434


86

Chapter 7: XML Parsing in Windows

Phone 7 and Android

This chapter discusses the XML parsing methods in Windows Phone 7 (WP7) and compares them with the parsing methods in Android.

XML Parsing in Windows Phone 7

In WP7, you can parse XML in two ways:

Using XMLReader Using LINQ to XML

SAXParser and DOMParser are not available in WP7. However, the XMLReader and LINQ to XML parsers function in the same way as these Android parsers.

XMLReader is a fast, forward-only, and a non-caching parser. In Android, you use the SAXParser API when you want a fast parser and want to minimize the memory footprint of your application. XMLReader is very similar to SAXParser.

LINQ to XML is an in-memory XML programming interface that enables you to edit XML documents. LINQ to XML is similar to DOMParser that you use in Java. DOM

parser loads the entire XML document to memory and allows you to use the DOM APIs to retrieve the data that you want.

You can use XMLReader to read very large XML documents. Loading large

documents to an in-memory tree uses a lot of memory and slows down performance. You can use LINQ to XML for parsing smaller XML documents.

XML Namespaces for Windows Phone 7

In WP7, the following namespaces are available for XML processing:

System.xml: Provides a standards-based support for processing XML

System.xml.Schema: Contains the XML classes that provide a standards-based support for XML Schema Definition (XSD)

System.xml.Linq: Contains the classes for LINQ to XML

System.xml.Serialization: Contains the classes that are used to serialize objects in XML documents or streams

XML Parsing Using XMLReader

XMLReader provides a forward-only and read-only access to a stream of XML data. XMLReader is similar to SAXParser. SAXParser parse XML node by node and


87

traverse a tree view from top to bottom. Here is a sample code that queries the

XML data stream to determine the current node type. This sample code uses XMLWriter to generate output the XMLReader content.

StringBuilder output = new StringBuilder(); String xmlString = @"<?xml version='1.0'?>  <Items> <Item>test with a child element <more/> stuff</Item> </Items>"; // Create an XmlReader , this is similar to creating SAXParser instance from SAXParserFactory in Android using (XmlReader reader = XmlReader.Create(new StringReader(xmlString))) { XmlWriterSettings ws = new XmlWriterSettings(); ws.Indent = true; using (XmlWriter writer = XmlWriter.Create(output, ws)) { // Parse the file and display each of the node. In Android, following iteration is done in handler implementation while using SAXParser while (reader.Read()) { switch (reader.NodeType) { case XmlNodeType.Element: // This is similar to startElement() method of handler in Android writer.WriteStartElement(reader.Name); break; case XmlNodeType.Text: writer.WriteString(reader.Value); break; case XmlNodeType.XmlDeclaration: case XmlNodeType.ProcessingInstruction: writer.WriteProcessingInstruction(reader.Name, reader.Value); break; case XmlNodeType.Comment: writer.WriteComment(reader.Value); break; case XmlNodeType.EndElement: // This is similar to endElement() method of handler in Android writer.WriteFullEndElement(); break; } } } }


88

SaxParser and XMLReader

This table shows a comparison of SAXParser and XMLReader:

SaxParser XMLReader

XML data is parsed node by node XML data is parsed node by node

XML data is not stored in the memory node

XML data is not stored in the memory node

Parsing occurs in the read-only node and the nodes cannot be inserted or deleted

Parsing occurs in the read-only node and the nodes cannot be inserted or deleted

Do a top to bottom traversal Do a forward-only traversal

XML Parsing using LINQ to XML

LINQ to XML provides a versatile in-memory XML programming API. With LINQ to

XML in WP7, you can perform all the operations that you come across while reading and manipulating XML data. LINQ to XML helps you to:

Load the XML data into phone memory in a variety of ways, such as from a

file or from XMLReader Create an XML tree from scratch

Insert the new XML elements into an in-memory XML tree Delete XML elements from an in-memory XML tree

Save XML to outputs, such as a file or XmlWriter

LINQ to XML is similar to DOMParser. However, unlike DOM, LINQ to XML provides a new object-model that is less resource consuming and is easier to work with.

In WP7, an application‟s memory-usage, including the UI components and images, cannot exceed 90 MB of the application's memory. Since XML parsing is resource

consuming, you need to consider your application's memory-usage while using the LINQ to XML API. As parsing XML can be resource consuming, use memory carefully while using the LINQ to XML API.

Note: A device whose memory exceeds 256 MB is exempted from the memory- usage restriction. You need to include the UI components, images and any other

content that are in memory, within that 90MB limit.

LINQ to XML Class Hierarchy


89

Although XElement is at a lower level in the class hierarchy, it is the fundamental class in LINQ to XML. XML trees are made up of XElements.

XAttributes are name or value pairs that are associated with an XElement. XDocuments are created only in certain scenarios, such as to hold a DTD or

a top level XML processing instruction (XProcessingInstruction). All the other XNodes can be the leaf nodes under an XElement or Xdocument, if they exist at the root level.

XAttribute and XNode are derived from the common base class XObject. XAttributes are not XNodes because the XML attributes are really the name-

value pairs that are associated with an XML element and not with nodes in the XML tree. This behavior of XAttribute is in contrast with W3C DOM.

XText and XCData are available in the present version of LINQ to XML.

However, it is best to think of them as a semi-hidden implementation except when exposing text nodes is necessary. You can retrieve the value of the

text within an element or attribute as a simple value, such as a string. XContainer is the only XNode that can have child elements. The child

elements can be an XDocument or XElement. The only XNode that can have children is an XContainer. The child elements are either an XDocument or XElement. An XDocument can contain an XElement (the root element), an

XDeclaration, an XDocumentType, or an XProcessingInstruction. An XElement can contain another XElement, an XComment, an

XProcessingInstruction, or text. You can parse the text that is contained in an XElement in a variety of formats. However, you need to represent the text as an XML tree.

Like the Document Class in Android, the XDocument Class in WP7 represents an in-memory XML document. See the sample code below. This sample code creates a

document, and then adds a comment and an element to the document. The sample code also creates another document using the results of a query. The XElement class, used in the sample code, is similar to Element class in Android.


90

StringBuilder output = new StringBuilder();

XDocument srcTree = new XDocument(

new XComment("This is a comment"),

new XElement("Root",

new XElement("Child1", "data1"),




new XElement("Info5", "info5"),



new XElement("Info8", "info8")

)

);

XDocument doc = new XDocument(

new XComment("This is a comment"),

new XElement("Root",

from el in srcTree.Element("Root").Elements()

where ((string)el).StartsWith("data")

select el

)

); // In Android to parse the XML tags using DOM, equivalent code is root.getElementsByTagName(ITEM);

output.Append(doc + Environment.NewLine);

OutputTextBlock.Text = output.ToString();

With DOMParser in Android, you write a series of statements to create an XML

document. In WP7, the coding constructs offer you flexibility and help in creating a well-structured code more easily.

In Android, you use DOMParser to build an XML tree from the bottom-up. With DOMParser, you create a document and elements, and then add the elements to the document. In addition to supporting this approach for constructing an XML tree,

LINQ to XML also supports functional construction. Functional construction uses the XElement and XAttribute constructors to build an XML tree. For example, consider

the following XML Data:

http://msdn.microsoft.com/en-us/library/system.xml.linq.xelement.aspx

http://msdn.microsoft.com/en-us/library/system.xml.linq.xattribute.aspx


91

<contacts>

<contact>

<name>Patrick Hines</name>

<phone type="home">206-555-0144</phone>

<phone type="work">425-555-0145</phone>

<address>

<street1>123 Main St</street1>

<city>Mercer Island</city>

<state>WA</state>

<postal>68042</postal>

</address>

<netWorth>10</netWorth>

</contact>

<contact>

<name>Gretchen Rivas</name>

<phone type="mobile">206-555-0163</phone>

<address>



<state>WA</state>


</address>


</contact>

<contact>

<name>Scott MacDonald</name>



<address>

<street1>345 Stewart St</street1>

<city>Chatsworth</city>

<state>CA</state>


</address>


</contact>

</contacts>

The following example constructs an XML tree by using LINQ to XML functional

construction:

XElement contacts =

new XElement("Contacts",

new XElement("Contact",

new XElement("Name", "Patrick Hines"),

new XElement("Phone", "206-555-0144",

new XAttribute("Type", "Home")),

new XElement("phone", "425-555-0145",

new XAttribute("Type", "Work")),

new XElement("Address",

new XElement("Street1", "123 Main St"),


92

new XElement("City", "Mercer Island"),

new XElement("State", "WA"),

new XElement("Postal", "68042")

)

)

);

After you indent the code, the XElement constructors resemble the structure of the underlying XML. The XElement constructor enables functional construction that

takes a params object. This is an example code snippet:

public XElement(XName name, params object[] contents)

The Contents parameter is flexible and supports an object that is a child of an

XElement. The parameters can be:

A string that is added as the text content. This is the recommended way to add a string as the value of an element. The LINQ to XML implementation

creates the internal XText node. An XText, which can have either a string or a CData value added as child

content. This parameter is useful for CData values since using a string is easy for ordinary string values.

An XElement that is added as a child element

An XAttribute that is added as an attribute An XProcessingInstruction or XComment, which is added as child content

An IEnumerable, which is enumerated and these rules are applied recursively

Anything to which the ToString() method is called and the result is added as

the text content. A Null parameter, which is ignored.

In this example below, a string Patrick Hines is passed in the name XElement constructor.

<contacts>

<contact>




<address>



<state>WA</state>


</address>


</contact>

<contact>



<address>


93



<state>WA</state>


</address>


</contact>

<contact>




<address>



<state>CA</state>


</address>


</contact>

</contacts>

Now, see the following scenario:

This string Patrick Hines can also be a variable. For example, new XElement

("name", custName)

This string Patrick Hines can also be a different type besides a string. For

example, a new XElement("quantity", 55). This data is the result of the following function call:

{ ... XElement qty = new XElement("quantity", GetQuantity()); ... } public int GetQuantity() { return 55; }

This string can also be an IEnumerable<XElement>. A common scenario is to use a query within a constructor to create the inner XML. The following code snippet reads contacts from an array of Person objects in a new XML

element Contacts.

class Person

{

public string Name;

public string[] PhoneNumbers;

}

var persons = new[] {

new Person {

Name = "Patrick Hines",


94

PhoneNumbers = new[] { "206-555-0144", "425-555-0145" }

},

new Person {

Name = "Gretchen Rivas",

PhoneNumbers = new[] { "206-555-0163" }

}

};

XElement contacts =

new XElement("contacts",

from p in persons

select new XElement("contact",

new XElement("name", p.Name),

from ph in p.PhoneNumbers

select new XElement("phone", ph)

)

);

The output of the code snippet is as follows:

<contacts>

<contact>


<phone>206-555-0144</phone>

<phone>425-555-0145</phone>

</contact>

<contact>


<phone>206-555-0163</phone>

</contact>

</contacts>

Notice how the repeating phone element is generated by queries that return an

IEnumerable for:

The inner body of the XML

The repeating Contact element Each contact

You can use the functional construction to design your output document. You can

either create the subtree of XML items inline, or call out to functions to do the work.


95

TRAVERSING XML

This section discusses the traditional approaches for navigating through an XML

tree. When XML is available in the in-memory, you usually have to navigate to the required XML elements. Language-Integrated Query provides powerful options for

performing this task.

Getting the Children of an XML Element

LINQ to XML offers ways to access the child elements of an XElement. To access all the child elements of an XElement or XDocument, you can use the Nodes() method.

This returns the IEnumerable<object> because you cannot have text along with the other LINQ to XML types. For example, you need to load the following XML in an XElement called contact:

<contact>

Met in 2005.


<phone>206-555-0144</phone>

<phone>425-555-0145</phone>



</contact>

Using the Nodes() methods, you can access all the child elements and generate the output by using this code fragment:

foreach (c in contact.Nodes()) {

//Output the results

}

This is the output:

Met in 2005.


<phone>206-555-0144</phone>

<phone>425-555-0145</phone>

For a more specific output, query for the content nodes of an XElement of a particular type. For example, consider accessing the XElement child elements only

for contact XElement. In this case, you can specify a parameterized type:

foreach (c in contact.Nodes().OfType<XElement>())


96

In the output, you will view only the child element:


<phone>206-555-0144</phone>

<phone>425-555-0145</phone>

To get all of the child elements of Contact, use this code:

foreach (x in contact.Elements())

In the output, you will view only the XElement children:


<phone>206-555-0144</phone>

<phone>425-555-0145</phone>

To get all the XElements with a specific name, use the Elements(XName) overload

that uses an XName as a parameter. For example, to view only the phone XElements, use the following code:

foreach (x in contact.Elements("phone"))

In the output, you will view the entire phone XElements:

<phone>206-555-0144</phone>

<phone>425-555-0145</phone>

Querying XML using LINQ to XML

This section describes how to use Language-Integrated Query with XML. The use of Language-Integrated Query in LINQ to XML distinguishes LINQ to XML from other

in-memory XML programming APIs.

Language-Integrated Query provides a consistent query experience across the different data models. Language-Integrated Query also provides the ability to mix

and match data models within a single query. Here are a few examples of using Language-Integrated Query across data models.

Standard query operators form a complete query language for IEnumerable<T>. The standard query operators show up as extension methods on any object that


97

implements IEnumerable<T>. You can use Standard query operators like any other

method.

This approach of calling query methods directly is called Explicit Dot Notation. Apart

from the query operators, there are query expressions for five common query operators:

Where

Select SelectMany

OrderBy GroupBy

The LINQ to XML integration with Language-Integrated Query is apparent in three

ways:

Leveraging Standard query operators

Using XML Query extensions Using XML Transformation

Leveraging Standard query operators is common with any Language-Integrated

Query enabled data access technology and contributes to a consistent query experience. Using XML Query extensions and Transformation, provide XML-specific

query and transform features.

Using Query Expressions with XML

This section shows a few examples of using the query expressions with LINQ to XML. Consider the following XML:

<contacts>

<contact>




<address>



<state>WA</state>


</address>


</contact>

<contact>



<address>



<state>WA</state>


</address>


</contact>

<contact>



98



<address>



<state>CA</state>


</address>


</contact>

</contacts>

The following query retrieves all contacts from location Washington and sorts the

contacts by name. The data is returned as string and is displayed in the IEnumerable<string> format.

from c in contacts.Elements("contact") where (string) c.Element("address").Element("state") == "WA" orderby (string) c.Element("name") select (string) c.Element("name");

This query retrieves all the contacts from Washington that have an area code 206. The result of this query is IEnumerable<XElement>.

from c in contacts.Elements("contact"), ph in c.Elements("phone") where (string) c.Element("address").Element("state") == "WA" && ph.Value.StartsWith("206") orderby (string) c.Element("name") select c;

In the following example, contacts that have a networth that is greater than the average networth are retrieved.

from c in contacts.Elements("contact"), average = contacts.Elements("contact"). Average(x => (int) x.Element("netWorth")) where (int) c.Element("netWorth") > average select c;


99

Summary

In this chapter we looked at XML parsing in Windows Phone 7. We also compared

XML parsing in Android and Windows Phone 7.

Related Resources

To know more about XML Data and Silverlight, visit:

http://msdn.microsoft.com/en-us/library/cc188996(v=vs.95).aspx

To know more about LINQ to XML for Windows Phone 7, visit:

http://msdn.microsoft.com/en-us/library/system.xml.linq(v=VS.95).aspx

To know more about processing XML Data with LINQ to XML (Silverlight):

http://msdn.microsoft.com/en-us/library/cc189074(v=VS.95).aspx

http://msdn.microsoft.com/en-us/library/cc188996(v=vs.95).aspx

http://msdn.microsoft.com/en-us/library/system.xml.linq(v=VS.95).aspx

http://msdn.microsoft.com/en-us/library/cc189074(v=VS.95).aspx

Technology

Wp7 guide for android developers