Android Development Tutorial

Android Development Tutorial

Based on Android 4.0

Lars Vogel

Version 9.8

Copyright © 2009, 2010, 2011, 2012 Lars Vogel

20.02.2012

Revision History

Revision 0.1 04.07.2009

Created

Revision 0.2 - 9.8 07.07.2009 - 20.02.2012

bug fixing and enhancements

Development with Android Gingerbread and Eclipse

This tutorial describes how to create Android applications with Eclipse. It is based on

Eclipse 3.7 (Indigo), Java 1.6 and Android 4.0 (Ice Cream Sandwich).

Table of Contents

1. What is Android?1.1. Android Operation System1.2. Security and permissions

2. Android components2.1. Activity2.2. Views and ViewGroups2.3. Intents

2.4. Services2.5. ContentProvider2.6. BroadcastReceiver2.7. (HomeScreen) Widgets2.8. Other

3. Android Development Tools3.1. What are the Android Development Tools?3.2. Dalvik Virtual Machine3.3. How to develop Android Applications

4. Android Application Architecture4.1. AndroidManifest.xml4.2. R.java and Resources4.3. Assets4.4. Reference to resources in XML files4.5. Activities and Layouts4.6. Activities and Lifecycle4.7. Context

5. Installation5.1. Pre-requisites for using a 64bit Linux5.2. Eclipse and automatic Android SDK5.3. Manually install Android SDK5.4. Install a specific Android version5.5. Android Source Code

6. Android virtual device - Emulator6.1. What is the Android Emulator?6.2. Google vrs. Android AVD6.3. Emulator Shortcuts6.4. Performance6.5. Hardware button

7. Tutorial: Create and run Android Virtual Device8. Error handling and typical problems

8.1. Clean Project8.2. Problems with Android Debug Bridge (adb)8.3. LogCat8.4. Emulator does not start8.5. Error message for @override8.6. Missing Imports8.7. Eclipse Tips

9. Your first Android project9.1. Create Project9.2. Two faces of things9.3. Create attributes9.4. Add UI Elements9.5. Edit UI properties9.6. Code your application9.7. Start Project

10. Starting an deployed application11. Menus and Action Bar

11.1. Definition of menu entries11.2. Action bar tabs11.3. Context menus

12. Tutorial: Menus and Action Bar12.1. Project

12.2. Add a menu XML resource13. Preferences14. Tutorial: Preferences

14.1. Using preferences14.2. Run

15. Layout Manager and ViewGroups15.1. Available Layout Manager15.2. LinearLayout15.3. RelativeLayout15.4. GridLayout

16. ScrollView17. Fragments

17.1. Overview17.2. When to use Fragments

18. Fragments Tutorial18.1. Overview18.2. Create project18.3. Create layouts for landscape mode18.4. Create Fragment classes18.5. Create layouts for landscape mode18.6. Activities18.7. Run

19. DDMS perspective and important views19.1. DDMS - Dalvik Debug Monitor Server19.2. LogCat View19.3. File explorer

20. Shell20.1. Android Debugging Bridge - Shell20.2. Uninstall an application via adb20.3. Emulator Console via telnet

21. Deploy your application on a real device22. Thank you23. Questions and Discussion24. Links and Literature

24.1. Source Code24.2. Android Resources24.3. vogella Resources

1. What is Android?

1.1. Android Operation System

Android is an operating system based on Linux with a Java programming interface.

The Android Software Development Kit (Android SDK) provides all necessary tools to

develop Android applications. This includes a compiler, debugger and a device

emulator, as well as its own virtual machine to run Android programs.

Android is currently primary developed by Google.

Android allows background processing, provides a rich user interface library, supports

2-D and 3-D graphics using the OpenGL libraries, access to the file system and

provides an embedded SQLite database.

Android applications consists out of different components and can re-use components

of other applications if these applications declare their components as available. This

leads to the concept of a task in Android, an application can re-use other Android

components to archive a task.

For example you can write an Application which integrates the a map component and a

camera component to archive a certain task.

1.2. Security and permissions

During deployment on an Android device, the Android system will create a unique user

and group ID for every Android application. Each application file is private to this

generated user, e.g. other applications cannot access these files.

In addition each Android application will be started in its own process.

Therefore by means of the underlying Linux operating system, every Android application

is isolated from other running applications. A misbehaving application cannot easily

harm other Android applications.

If data should be shared the application must do this explicitly, e.g. via a Service or

a ContentProvider.

Android also contains a permission system. Android predefines permissions for certain

tasks but every application can also define its own permissions.

An application must declare in its configuration file (AndroidManifest.xml) that it requires

certain permissions.

Depending on the details of the defined permission, the Android system will during

installation either automatically grant the permission, reject it or ask the user if he grants

these permissions to the application.

If for example the application declares that is requires Internet access then the user

need to confirm this during installation.

This is called "user driven security". The user decides to grant a permission or to deny

it. If the user does not want to give all permissions required by the application, this

application cannot be installed. The check of the permission is only performed during

installation, permissions cannot be denied or granted after the installation.

Typically not all users check the permissions in detail but some users do and if there is

something strange with them, they will write bad reviews on the corresponding Android

markets.

2. Android components

The followings gives a short overview of important Android components.

2.1. Activity

Activity represents the presentation layer of an Android application. A simplified (and

slightly incorrect) description is that an Activity is a a screen. This is slightly incorrect

as Activities can be displayed as dialogs or transparent. An Android application can

have several Activities.

2.2. Views and ViewGroups

Views are user interface widgets, e.g. buttons or text fields. The base class for

all Views isandroid.view.View. Views often have attributes which can be used to change

their appearance and behavior.

A ViewGroup is responsible for arranging other Views e.g. they are layout manager. The

base class for a layout manager is android.view.ViewGroups. ViewGroup also

extends View. ViewGroups can be nestled to create complex layouts. You should not

nestle ViewGroups too deeply as this has a negative impact on performance.

2.3. Intents

Intents are asynchronous messages which allow the application to request functionality

from other components of the Android systen, e.g. from Services or Activities. An

application can call a component directly (explicit intent) or ask the Android system to

evaluate registered components for a certain Intents (implicit intents). For example the

application could implement sharing of data via an Intent and all components which

allow sharing of data would be available for the user to select. Applications register

themselves to an intent via an IntentFilter.Intents allow to combine loosely coupled

components to perform certain tasks.

2.4. Services

Services perform background tasks without providing an UI. They can notify the user

via the notification framework in Android.

2.5. ContentProvider

ContentProvider provides an structured interface to data. Via a ContentProvider your

application can share data with other applications. Android contains an SQLite database

which is frequently used in conjunction with a ContentProvider to persists the data of

the ContentProvider.

2.6. BroadcastReceiver

BroadcastReceiver can be registered to receives system messages

and Intents. BroadcastReceiverwill get notified by the Android system if the specified

situation happens. For example a BroadcastReceivercould get called once the system

completed its boot process or if a phone call is received.

2.7. (HomeScreen) Widgets

Widgets are interactive components which are primary used on the Android

homescreen. They typically display some kind of data and allow the user to perform

actions via them. For example a Widget could display a short summary of new emails

and if the user select a email it could start the email application with the selected email.

2.8. Other

Android provide much more components but the list above describes the most important

ones. Other Android components are "Live Folders" and "Live Wallpapers". Live Folders

display data on the homescreen without launching the corresponding application.

3. Android Development Tools

3.1. What are the Android Development Tools?

Google provides the Android Development Tools (ADT) to develop Android applications

with Eclipse. ADT is a set of plug-in which extended the Eclipse IDE with Android

development capabilities.

ADT contains all required functionality to create, compile, debug and deploy Android

applications from the Eclipse IDE and from the command line. Other IDE's, e.g. IntellJ,

are also reusing components of ADT.

ADT also provides an Android device emulator, so that Android applications can be

tested without a real Android phone.

3.2. Dalvik Virtual Machine

The Android system uses a special virtual machine, i.e. the Dalvik Virtual Machine to

run Java based applications. Dalvik uses special bytecode which is different from Java

bytecode.

Therefore you cannot run standard Java bytecode on Android.

3.3. How to develop Android Applications

Android applications are primary written in the Java programming language. The Java

source files are converted to Java class files by the Java compiler.

Android provides a tool dx which converts Java class files into a dex (Dalvik Executable)

file. All class files of one application are placed in one compressed .dex file. During this

conversion process redundant information in the class files are optimized in the .dex file.

For example if the same String in different class file is found, the .dex file is stored only

once and reference this String in the corresponding classes.

.dex files are therefore much smaller in size then the corresponding class files.

The .dex file and the resources of an Android project, e.g. the images and XML files are

packed into an .apk(Android Package) file. The program aapt (Android Asset Packaging

Tool) perform this packaging.

The resulting .apk file contains all necessary data to run the Android application and can

be deployed to an Android device via the "adb" tool.

The Android Development Tools (ADT) allows that all these steps are performed

transparent to the user; either within Eclipse or via the command line.

If you use the ADT tooling you press a button or run a script and the whole Android

application (.apk file) will be created and deployed.

4. Android Application Architecture

4.1. AndroidManifest.xml

An Android application is described in the file AndroidManifest.xml. This file must

declare all components, e.g. Activities and Services of the application.

It must also contain the required permissions for the application. For example if the

application requires network access it must be specified here.

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="de.vogella.android.temperature"

android:versionCode="1"

android:versionName="1.0">

<application android:icon="@drawable/icon" android:label="@string/app_name">

<activity android:name=".Convert"

android:label="@string/app_name">

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

</application>

<uses-sdk android:minSdkVersion="9" />

</manifest>

The package attribute defines the base package for the following Java elements.

The Android Marketplace requires that very application uses its own unique package.

Therefore it is a good habit to use as package name your reverse domain name. This

will avoid collisions with other developers.

android:versionName and android:versionCode specify the version of your

application. versionNameis what the user sees and can be any string.

versionCode must be an integer. The Android Market determine based

on versionCode if an update of an Android applications on devices is required. You

typically start with "1" and increase this value by one, if you roll-out a new version of

your application.

The tag <activity> defines an Activity, in this example pointing to

thede.vogella.android.temperature.Convert class. An intent filter is registered for this

class which defines that this Activity is started once the application starts

(actionandroid:name="android.intent.action.MAIN" ). The category

definition category android:name="android.intent.category.LAUNCHER" defines that

this application is added to the application directory on the Android device.

The @string/app_name value refer to resource files which contain the actual values.

This makes it easy to provide different resources, e.g. strings, colors, icons, for different

devices and makes it easy to translate applications.

The "uses-sdk" part of the "AndroidManifest.xml" file defines the minimal SDK version

for which your application is valid. This will prevent your application being installed on

devices with older SDK versions.

4.2. R.java and Resources

The " gen " directory in an Android project contains generated values. R.java is a

generated class which contains references to certain resources of the the project.

These resources must be defined in the res directory and can be XML files, icons or

pictures. Via XML files you can for example define values, menus, layouts or

animations.

If you create a new resource, the corresponding reference is automatically created

in R.java. These references are static int values and define ID's for the resources.

The Android system provides methods to access the corresponding resource via these

ID's.

For example to access a String with the reference id R.string.yourString use the

methodgetString(R.string.yourString));.

R.java is automatically created by the Eclipse development environment, manual

changes are not necessary.

4.3. Assets

While the directory res is contains structured values which are known to the Android

platform the directory assetscan be used to store any kind of data. In Java you can

access this data via the AssetsManager and thegetAssets() method .

4.4. Reference to resources in XML files

In your XML files, e.g. your layout files, you can refer to other resources via the @ sign.

For example if you want to refer to a color you defined as resources you can refer to it

via @color/your_id or if you have defined a "hello" string as resource you can access it

via @string/hello .

4.5. Activities and Layouts

The user interface for Activities is defined via layouts. The layout defines the

include Views (widgets) and their properties.

A layout can be defined via Java code or via XML. You typically uses Java code to

generate the layout if you don't know the content until runtime; for example if your layout

depends on content which you read from the Internet.

XML based layouts are defined via a resource file in the folder /res/layout . This file

specifies theViewGroups, Views, their relationship and their attributes for a specific

layout. If a UI element needs to be accessed via Java code you have to give the UI

element an unique id via the android:id attribute. To assign a new id to an UI element

use @+id/yourvalue. By conversion this will create and assign a new id yourvalue to the

corresponding UI element. In your Java code you can later access these UI elements

via the methodfindViewById(R.id.yourvalue).

Defining layouts via XML is usually the preferred way as this separates the

programming logic from the layout definition. It also allows the definition of different

layouts for different devices. You can also mix both approaches.

4.6. Activities and Lifecycle

The operating system controls the life cycle of your application. At any time the Android

system may stop or destroy your application, e.g. because of an incoming call. The

Android system defines a life cycle for activities via pre-defined methods. The most

important methods are:

onSaveInstanceState() - called if the activity is stopped. Used to save data so

that the activity can restore its states if re-started

onPause() - always called if the Activity ends, can be used to release resource or

save data

onResume() - called if the Activity is re-started, can be used to initialize fields

The activity will also be restarted if a so called "configuration change" happens. A

configuration change for example happens if the user changes the orientation of the

device (vertical or horizontal). The activity is in this case restarted to enable the Android

platform to load different resources for these configuration, e.g. layouts for vertical or

horizontal mode. In the emulator you can simulate the change of the orientation

via CNTR+F11.

You can avoid a restart of your application for certain configuration changes via the

configChanges attribute on your activity definition in your AndroidManifest.xml. The

following activity will not be restarted in case of orientation changes or position of the

physical keyboard (hidden / visible).

<activity android:name=".ProgressTestActivity"

android:label="@string/app_name"

android:configChanges="orientation|keyboardHidden|keyboard">

</activity>

4.7. Context

The class android.content.Context provides the connections to the Android system. It

is the interface to global information about the application environment. Context also

provides access to Android Services, e.g. theLocation Service. As Activities and

Services extend the class Context you can directly access the context viathis.

5. Installation

The following assume that you have already Eclipse installed. For details please

see Eclipse Tutorial

5.1. Pre-requisites for using a 64bit Linux

The Android SDK is 32bit, therefore on an 64bit Linux system you need to have the

package ia32-libs installed. For Ubuntu you can do this via the following command.

apt-get install ia32-libs

Please check your distribution documentation if you are using a different flavor of Linux.

5.2. Eclipse and automatic Android SDK

Use the Eclipse update manager to install all available components for the Android

Development Tools (ADT) from the URL https://dl-ssl.google.com/android/eclipse/. If

you are not familiar with the Eclipse update manager the usage is described in Eclipse

update manager.

After the new Android development components are installed you will be prompted to

install the Android SDK. You can use the following wizard or go to the next section to

learn how to do it manually.

5.3. Manually install Android SDK

The previous step downloads the Android SDK automatically for you. You can also

download the Android SDK from the Android SDK download page.

The download contains a zip file which you can extract to any place in your file system,

e.g. I placed it under "c:\android-sdk-windows". Avoid using spaces in the path name

otherwise you may experience problems later.

You also have to define the location of the Android SDK in the Eclipse Preferences. In

Eclipse open the Preferences dialog via Windows → Preferences. Select Android and

enter the installation path of the Android SDK.

5.4. Install a specific Android version

The Android SDK Manager allows you to install specific versions of Android.

Select Window → Android SDK Manager from the Eclipse menu.

The dialog allows you to install new packages and also allows you to delete them.

Select "Available packages" and open the "Third Party Add-ons". Select the Google API

14 (Android 4.0) version of the SDK and press "Install".

Press the "Install" button and confirm the license for all packages. After the installation

completes, restart Eclipse.

5.5. Android Source Code

The following step is optional.

5.5.1. As of Android 4.0

During Android development it is very useful to have the Android source code available

as Android uses a lot of defaults.

As of Android 4.0 the Android development tools provides also the source code. You

can download it via the Android SDK Manager by selecting the "Sources for Android

SDK".

The sources are downloaded to the source directory located in

"path_to_android_sdk/sources/android-xx". xx is the api level number (15 for 4.0.3).

In the Eclipse Package Explorer, right click on your android.jar and

select Properties → Java Source Attachment. Type in the source directory name and

press OK. Afterwards you can browse through the source code.

5.5.2. Prior to Android 4.0

For earlier versions Haris Peco maintains plugins, which provide the Android Source

code code. Use the Eclipse update manager to install the Android Source plugin from

the following update site:

"http://adt-addons.googlecode.com/svn/trunk/source/com.android.ide.eclipse.source.up

date".

More details can be found on the project website.

6. Android virtual device - Emulator

6.1. What is the Android Emulator?

The Android Development Tools (ADT) include an emulator to run an Android system.

The emulator behaves like a real Android device (in most cases) and allows you to test

your application without having a real device.

You can configure the version of the Android system you would like to run, the size of

the SD card, the screen resolution and other relevant settings. You can define several

devices with different configurations.

Via the emulator you select which device should be started, you can also start several in

parallel. These devices are called "Android Virtual Device" (AVD).

The ADT allow to deploy and run your Android program on the AVD.

6.2. Google vrs. Android AVD

During the creation of an AVD you decide if you want an Android device or an Google

device.

An AVD created for Android will contain the programs from the Android Open Source

Project. An AVD created for the Google API's will also contain several Google

applications, most notable the Google Maps application.

If you want to use functionality which is only provided via the Google API's, e.g.

Cloud2DeviceMessaging or Google Maps you must run this application on an AVD with

Google API's.

6.3. Emulator Shortcuts

Obviously you can use the emulator via the keyboard on the right side of the emulator.

But there are also some nice shortcuts which are useful.

Alt+Enter Maximizes the emulator. Nice for demos.

Ctrl+F11 changes the orientation of the emulator.

F8 Turns network on / off.

6.4. Performance

Try to use a smaller resolution for your emulator as for example HVGA. The emulator

gets slower the more pixels its needs to render as it is using software rendering.

Also if you have sufficient memory on your computer, add at least 1 GB of memory to

your emulator. This is the value "Device ram size" during the creation of the AVD.

Also set the flag "Enabled" for Snapshots. This will save the state of the emulator and

let it start much faster.

6.5. Hardware button

Android 4.0 introduced that devices do not have to have hardware button anymore. If

you want to create such an AVD, add the "Hardware Back/Home keys" property to the

device configuration and set it to "false".

7. Tutorial: Create and run Android Virtual Device

To define an Android Virtual Device (ADV) open the "AVD Manager"

via Windows → AVD Manager and press "New".

Enter the following.

We can also select the box "Enabled" for Snapshots. This will make the second start of

the virtual device much faster.

At the end press the button "Create AVD". This will create the AVD configuration and

display it under the "Virtual devices".

To test if your setup is correct, select your device and press "Start".

After (a long time) your AVD starts. You are able to use it via the mouse and via the

virtual keyboard of the emulator.

8. Error handling and typical problems

Things are not always working as they should. This section gives an overview over

typical problems and how to solve them.

8.1. Clean Project

Several users report that get the following errors:

1. Project ... is missing required source folder: 'gen'

2. The project could not be built until build path errors are resolved.

3. Unable to open class file R.java.

To solve any of these errors, go to the project menu and select Project → Clean.

8.2. Problems with Android Debug Bridge (adb)

The communication with the emulator or your Android device might have problems. This

communication is handled by the Android Debug Bridge (adb).

Eclipse allows to reset the adb in case this causes problems. Select therefore the

DDMS perspective via Window →Open Perspective → Other → DDMS

To restart the adb, select the "Reset adb" in the Device View.

8.3. LogCat

The "LogCat" View shows you the log messages of your Android device and help you

analyze problems. For example Java exceptions in your program would be shown here.

To open this view, select Window → Show View →Other → Android → LogCat.

8.4. Emulator does not start

If your emulator does not start, make sure that the android-sdk version is in a path

without any spaces in the path name.

8.5. Error message for @override

The @override annotation was introduced in Java 1.6. If you receive an error message

for @override, change the Java compiler level to Java 1.6. To do this right-click on the

project, select Properties → Java Compiler → Compiler compliance level and select

"1.6" in the drop-down box.

8.6. Missing Imports

Java requires that classes which are not part of the standard Java Language be either

fully qualified or declared via imports.

If you see error message with "XX cannot be resolved to a variable", right-click in

your Editor and select Source →Organize Imports to important required packages.

8.7. Eclipse Tips

To work more efficiently with Eclipse,

select Window → Preferences → Java → Editor → Save Actions and select that the

source code should be formatted and that the imports should be organized at every

save.

1. Conventions for the tutorials

Table of Contents

1. API version, package and application name2. Warnings Messages for Strings

1. API version, package and application name

The tutorials of this document have been developed and tested with Android 4.0.3, API

Level 15. Please use this version for all tutorials in this book. Higher version usually

should also work. Lower version of the Android API might also work, but if you face

issues, try the recommended version.

The base package for the projects is always the same as the project name, e.g. if you

are asked to create a project "de.vogella.android.example.test" then the corresponding

package name is "de.vogella.android.example.test".

The Application name, which must be entered on the Android project generation wizard,

will not be predefined. Choose a name you like.

2. Warnings Messages for Strings

The Android development tools are show warnings if you use hard-coded strings, for

example in layout files. While for real application its best practice to use string resource

files we use use Strings directly to simplify the creation of the examples.

9. Your first Android project

9.1. Create Project

This app is also available on the Android Marketplace. Search for "vogella" for find this

example.

Select File → New → Other → Android → Android Project and create the Android

project "de.vogella.android.temperature". Enter the following.

Press "Finish". This should create the following directory structure.

While "res" contains structured values which are known to the Android platform the

directory "assets" can be used to store any kind of data. In Java you can access this

data via the AssetsManager and the method getAssets().

9.2. Two faces of things

The Android SDK allows the developer to define certain artifacts, e.g. strings and UI's,

in two ways: via a rich editor, and directly via XML.

The following description tries to use the rich UI but for validation the resulting XML is

also displayed. You can switch between both things by clicking on the tab on the lower

part of the screen. For example in the Package Explorer select "res/layout/main.xml".

9.3. Create attributes

Android allows you to create attributes for resources, e.g. for strings or colors. These

attributes can be used in your UI definition via XML or in your Java source code.

Select the file "res/values/string.xml" and press "Add". Select "Color" and enter

"myColor" as the name and "#3399CC" as the value.

Add also the following "String" attributes. String attributes allow the developer to

translate the application at a later point.

Table 1. String Attributes

Name Value

celsius to Celsius

fahrenheit to Fahrenheit

calc Calculate

Switch to the XML representation and validate the values.


<resources>

<string name="hello">Hello World, Convert!</string>

<string name="app_name">Temperature Converter</string>

<color name="myColor">#3399CC</color>

<string name="myClickHandler">myClickHandler</string>

<string name="celsius">to Celsius</string>

<string name="fahrenheit">to Fahrenheit</string>

<string name="calc">Calculate</string>

</resources>

9.4. Add UI Elements

Select "res/layout/main.xml" and open the Android editor via a double-click. This editor

allows you to create the UI via drag and drop or via the XML source code. You can

switch between both representations via the tabs at the bottom of the editor. For

changing the position and grouping elements you can use the outline view.

The following shows a screenshot of the Palette view from which you can drag and drop

new UI elements into your layout. Please note that the "Palette" view changes

frequently so your view might be a bit different.

Right-click on the text object “Hello World, Hello!” in the layout. Select Delete on the

popup menu to remove the text object. Then, from the “Palette” view, select Text Fields

and locate “Plain Text”. Drag this onto the layout to create a text input field. All object

types in the section "Text Fields” derive from the class "EditText", they just specify via

an additional attribute which text type can be used.

Now select the Palette section “Form Widgets” and drag a “RadioGroup” object onto the

layout. The number of radio buttons added to the radio button group depends on your

version of Eclipse. Make sure there are two radio buttons by deleting or adding radio

buttons to the group.

From the Palette section Form Widgets, drag a Button object onto the layout.

The result should look like the following.

Switch to "main.xml" and verify that your XML looks like the following.


<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical" android:layout_width="fill_parent"

android:layout_height="fill_parent">

<EditText android:layout_height="wrap_content" android:id="@+id/editText1"

android:layout_width="match_parent" android:text="EditText"></EditText>

<RadioGroup android:layout_height="wrap_content" android:id="@+id/radioGroup1"

android:layout_width="match_parent">

<RadioButton android:text="RadioButton"

android:layout_width="wrap_content" android:id="@+id/radio0"

android:layout_height="wrap_content" android:checked="true"></RadioButton>

<RadioButton android:text="RadioButton"

android:layout_width="wrap_content" android:id="@+id/radio1"

android:layout_height="wrap_content"></RadioButton>

</RadioGroup>

<Button android:text="Button" android:id="@+id/button1"

android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>

</LinearLayout>

9.5. Edit UI properties

If you select a UI element you can change its properties via the properties view. Most of

the properties can be changed via the right mouse menu. You can also edit properties

of fields directy in XML. Typically you change properties directly in the XML file as this is

much faster. But the right mouse functionality is nice if you are searching for a certain

property.

Open your file "main.xml" We will delete the initial text for the EditText field in XML.

Switch to the XML tab called "main.xml" and delete

the android:text="EditText" property from the EditText part. Switch back to the

"Graphical Layout" tab and check that the text is removed.

Use the right mouse click on the first radio button to assign the "celsius" string attribute

to its "text" property. Assign the and "fahrenheit" string attribute to the second radio

button.

From now on I assume you are able to use the properties menu on the UI elements.

You can either edit the XML file or modify the properties via right mouse click.

Set the property "Checked" to true for the first RadioButton. Assign "calc" to the text

property of your button and assign "myClickHandler" to the "onClick" property. Set the

"Input type" property to "numberSigned" and "numberDecimal" on your EditText.

All your other UI controls are contained in a LinearLayout. We want to assign a

background color to this LinearLayout. Right-click on an empty space in Graphical

Layout mode, then select Other Properties → All by Name→ Background. Select

“Color” and then “myColor” in the list.

Switch to the "main.xml" tab and verify that the XML is correctly maintained.



android:orientation="vertical" android:layout_width="fill_parent"

android:layout_height="fill_parent" android:background="@color/myColor">

<EditText android:layout_height="wrap_content" android:id="@+id/editText1"

android:layout_width="match_parent" android:inputType="numberDecimal|numberSigned"></EditText>

<RadioGroup android:layout_height="wrap_content" android:id="@+id/radioGroup1"

android:layout_width="match_parent">

<RadioButton android:layout_width="wrap_content"

android:id="@+id/radio0" android:layout_height="wrap_content"

android:text="@string/celsius" android:checked="true"></RadioButton>

<RadioButton android:layout_width="wrap_content"

android:id="@+id/radio1" android:layout_height="wrap_content"

android:text="@string/fahrenheit"></RadioButton>

</RadioGroup>

<Button android:id="@+id/button1" android:layout_width="wrap_content"

android:layout_height="wrap_content" android:text="@string/calc"

android:onClick="myClickHandler"></Button>

</LinearLayout>

9.6. Code your application

During the generation of your new Android project you specified that

an Activity called ConvertActivityshould get created. The project wizard also created

the corresponding Java classs.

Change your code in ConvertActivity.java to the following. Note that

the myClickHandler will be called based on the OnClick property of your button.

package de.vogella.android.temperature;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.EditText;

import android.widget.RadioButton;

import android.widget.Toast;

public class ConvertActivity extends Activity {

private EditText text;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

text = (EditText) findViewById(R.id.editText1);

}

// This method is called at button click because we assigned the name to the

// "On Click property" of the button

public void myClickHandler(View view) {

switch (view.getId()) {

case R.id.button1:

RadioButton celsiusButton = (RadioButton) findViewById(R.id.radio0);

RadioButton fahrenheitButton = (RadioButton) findViewById(R.id.radio1);

if (text.getText().length() == 0) {

Toast.makeText(this, "Please enter a valid number",

Toast.LENGTH_LONG).show();

return;

}

float inputValue = Float.parseFloat(text.getText().toString());

if (celsiusButton.isChecked()) {

text.setText(String

.valueOf(convertFahrenheitToCelsius(inputValue)));

celsiusButton.setChecked(false);

fahrenheitButton.setChecked(true);

} else {

text.setText(String

.valueOf(convertCelsiusToFahrenheit(inputValue)));

fahrenheitButton.setChecked(false);

celsiusButton.setChecked(true);

}

break;

}

}

// Converts to celsius

private float convertFahrenheitToCelsius(float fahrenheit) {

return ((fahrenheit - 32) * 5 / 9);

}

// Converts to fahrenheit

private float convertCelsiusToFahrenheit(float celsius) {

return ((celsius * 9) / 5) + 32;

}

}

9.7. Start Project

To start the Android Application, select your project, right click on it, and select Run-

As → Android Application. Be patient, the emulator starts up very slowly.

You should get the following result.

Type in a number, select your conversion and press the button. The result should be

displayed and the other option should get selected.

10. Starting an deployed application

After you run your application on the virtual device you can start it again on the device.

If you press the Home button you can also select your application.

11. Menus and Action Bar

11.1. Definition of menu entries

Android provides two possible ways to display global actions which the user can select.

The first one is the usage of the Action Bar in the application. The Action Bar is a

window feature at the top of the activity that may display the activity title, navigation

modes, and other interactive items.

The second option is that the app can open a menu which shows additional actions via

a popup menu. Typically you define your menu entries in a way that they are added to

the action bar if sufficient space is available in the action bar and if not, remaining menu

items are displayed in the popup menu.

The option menu and the action bar of your activity is filled by the method

onCreateOptionsMenu() of your activity.

The ActionBar also shows an icon of your application. You can also add an action to

this icon. If you select this icon the onOptionsItemSelected() method will be called with

the value android.R.id.home. The recommendation is to return to the main Activity in

your program.

// If home icon is clicked return to main Activity

case android.R.id.home:

Intent intent = new Intent(this, OverviewActivity.class);

intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

startActivity(intent);

break;

In this method you can create the menu programmatically or you can use a pre-defined

XML resources which you inflate via the MenuInflator class. Each Activity has

already an instance of the class available and this instance can get accessed via

the getMenuInflator() method.

The onCreateOptionsMenu() method is only called once. If you want to influence the

menu later you have to use the onPrepareOptionsMenu() method.

11.2. Action bar tabs

It is also possible to add tabs to an action bar.

11.3. Context menus

You can also assign a context menu to an UI widget (view). A context menu is activated

if the user "long presses" the view.

A context menu for a view is registered via the registerForContextMenu(view) method.

TheonCreateContextMenu() method is called every time a context menu is activated as

the context menu is discarded after its usage. The Android platform may also add

options to your View, e.g. EditText provides context options to select text, etc.

12. Tutorial: Menus and Action Bar

12.1. Project

This chapter will demonstrate how to create and evaluate a option menu which is

displayed in the action bar if sufficient space is available. This example will be extended

in the chapter about preferences.

Create a project called "de.vogella.android.socialapp" with the Activity called

"OverviewActivity". Change the "main.xml" layout file in the diretory "/res/layout/" to the

following:



android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

<Button

android:id="@+id/Button01"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Show Preferences" >

</Button>

<Button




android:text="Change Preferences" >

</Button>

</LinearLayout>

12.2. Add a menu XML resource

Select your project, right click on it and select New → Other → Android → Android XML

File to create a new XML resource.

Select the option "Menu", enter as File "mainmenu.xml" and press the button "Finish".

This will create a new file "mainmenu.xml" in the folder "res/menu" of your project.

Android provides a nice editor to edit this file, unfortunately this editor is not always

automatically used due to bugs in the ADT. If that happens, you can open this editor

manually. Right-click on your menu file and select Open with → Android Menu Editor.

Switch if necessary to the "Layout" tab of the editor. Press Add and select "Item".

Maintain the following value. This defines the entries in your menu. We will also define

that the menu entry is displayed in the action bar if there is sufficient space available.

Change your Activity class "OverviewActivity" to the following. The

OnCreateOptionsMenu method is used to create the menu. The behavior in

"onOptionsItemSelected" is currently hard-coded to show a Toast and will soon call the

preference settings. In case you want to disable or hide menu items you can use the

method "onPrepareOptionsMenu" which is called every time the menu is called.

package de.vogella.android.socialapp;



import android.view.Menu;

import android.view.MenuInflater;

import android.view.MenuItem;


public class OverviewActivity extends Activity {

@Override




}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

MenuInflater inflater = getMenuInflater();

inflater.inflate(R.menu.mainmenu, menu);

return true;

}

@Override

public boolean onOptionsItemSelected(MenuItem item) {

Toast.makeText(this, "Just a test", Toast.LENGTH_SHORT).show();

return true;

}

}

Run your application. As there is enough space in the action bar your item will be

displayed there. If there would be more items you could press "Menu" on the emulator

to see them. If you select the menu item you should see a small info message.

The two "Preference" buttons are not yet active. We will use them in the next chapter.

13. Preferences

Android supports the usage of Preferences to allow you to save data for your

application. Preferences are stored as key values. The definition of Preferences can

also be done via an XML resource.

Android provides the class "PreferenceActivity" which extends the class Activity.

PreferenceActivity supports the simple handling of preferences. This activity can load a

preference definition resources via the method addPreferencesFromResource().

To communicate between different components Android uses Intents. Typically the

PreferenceActivity is started from another activity via an Intent.

In your application you can access the preference manager via the following:

SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);

Values can get access via the key of the preference setting.

String username = preferences.getString("username", "n/a");

To create or change preferences you have to call the edit() methods. Once you have

changed the value you have to call commit() to apply your changes.

Editor edit = preferences.edit();

edit.putString("username", "new_value_for_user");

edit.commit();

14. Tutorial: Preferences

14.1. Using preferences

We will continue using the example project "de.vogella.android.social".

Create an Android XML resource "preferences.xml" of type "PreferenceScreen".

Open the file via right-mouse click and Open-with → Android XML Resource Editor.

Press Add, add a "PreferenceCategory" and add two preferences "EditTextPreferences"

to this category : "User" and "Password".

You can also enter values for other properties of EditTextField, e.g. the inputMethod.

Add the following attribute to the XML definition of your password field to make the input

quoted with *.

android:inputType="textPassword"

Create the class MyPreferencesActivity which extends PreferenceActivity.

This Activity will load the "preference.xml" file and will allow the user to change the

values.



import android.preference.PreferenceActivity;

public class MyPreferencesActivity extends PreferenceActivity {

@Override



addPreferencesFromResource(R.xml.preferences);

}

}

To make this class available as an activity for Android you need to register it in your

"AndroidManifest.xml" file. Select "AndroidManifest.xml" and the tab "Application". Scroll

to the botton of the view and add your new activity via the "Add" button.

To make use of our new preference activity and the preference values we adjust the

"OverviewActivity". The first button will show the current values of the preferences via a

Toast and the second button will revert the maintained user name to demonstrate how

you could change the preferences via code.



import android.content.SharedPreferences;

import android.content.SharedPreferences.Editor;


import android.preference.PreferenceManager;

import android.view.Menu;

import android.view.MenuInflater;

import android.view.MenuItem;


import android.view.View.OnClickListener;

import android.widget.Button;


public class OverviewActivity extends Activity {

SharedPreferences preferences;

@Override




Button button = (Button) findViewById(R.id.Button01);

// Initialize preferences

preferences = PreferenceManager.getDefaultSharedPreferences(this);

button.setOnClickListener(new OnClickListener() {

public void onClick(View v) {


String password = preferences.getString("password", "n/a");

showPrefs(username, password);

}

});

Button buttonChangePreferences = (Button) findViewById(R.id.Button02);

buttonChangePreferences.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

updatePreferenceValue();

}

});

}

private void showPrefs(String username, String password){

Toast.makeText(

OverviewActivity.this,

"Input: " + username + " and password: "

+ password, Toast.LENGTH_LONG).show();

}

private void updatePreferenceValue(){

Editor edit = preferences.edit();


// We will just revert the current user name and save again

StringBuffer buffer = new StringBuffer();

for (int i = username.length() - 1; i >= 0; i--) {

buffer.append(username.charAt(i));

}

edit.putString("username", buffer.toString());

edit.commit();

// A toast is a view containing a quick little message for the

// user. We give a little feedback

Toast.makeText(OverviewActivity.this,

"Reverted string sequence of user name.",


}

To open the new preference Activity we will use

the onOptionsItemSelected() method. Even though we currently have only one option

in our menu we use a switch to be ready for several new menu entries. To see the

current values of the preferences we define a button and use the

class PreferenceManager to get the sharedPreferences.

@Override

public boolean onCreateOptionsMenu(Menu menu) {

MenuInflater inflater = getMenuInflater();

inflater.inflate(R.menu.mainmenu, menu);

return true;

}

// This method is called once the menu is selected

@Override

public boolean onOptionsItemSelected(MenuItem item) {

switch (item.getItemId()) {

// We have only one menu option

case R.id.preferences:

// Launch Preference activity

Intent i = new Intent(OverviewActivity.this, MyPreferencesActivity.class);

startActivity(i);

// Some feedback to the user

Toast.makeText(OverviewActivity.this, "Enter your user credentials.",


break;

}

return true;

}

14.2. Run

Run your application. Press the "menu" hardware button and then select your menu

item "Preferences". You should be able to enter your user settings then press the back

hardware button to return to your main activity. The saved values should be displayed in

a small message windows (Toast) if you press your first button. If you press the second

button the username should be reversed.

15. Layout Manager and ViewGroups

15.1. Available Layout Manager

A layout manager is a subclass of ViewGroup and is responsible for the layout of itself

and its child Views. Android supports different default layout managers.

As of Android 4.0 the most relevant layout manager

are LinearLayout, FrameLayout, RelativeLayout andGridLayout.

All layouts allow the developer to define attributes. Children can also define attributes

which may be evaluated by their parent layout.

AbsoluteLayoutLayout is deprecated and TableLayout can be implemented more

effectively viaGridLayout

15.2. LinearLayout

LinearLayout puts all its child elements into a single column or row depending on

the android:orientationattribute. Possible values for this attribute

are horizontal and vertical, horizontal is the default value.

LinearLayout can be nested to achieve more complex layouts.

15.3. RelativeLayout

RelativeLayout allow to position the widget relative to each other. This allows for

complex layouts.

A simple usage for RelativeLayout is if you want to center a single component. Just

add one component to theRelativeLayout and set

the android:layout_centerInParent attribute to true.


<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"


<ProgressBar

android:id="@+id/progressBar1"

style="?android:attr/progressBarStyleLarge"



android:layout_centerInParent="true"

/>

</RelativeLayout>

15.4. GridLayout

15.4.1. Overview

GridLayout was introduced with Android 4.0. This layout allows you to organize a view

into a Grid. GridLayout separates its drawing area into: rows, columns, and cells.

You can specify how many columns you want for define for each View in which row and

column it should be placed and how many columns and rows it should use. If not

specified GridLayout uses defaults, e.g. one column, one row and the position of

a View depends on the order of the declaration of the Views.

15.4.2. Tutorial GridLayout

Create the project "de.vogella.android.layout.gridlayout" with the Activity called

"DemoGridLayout".

Change "main.xml" to the following.


<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:id="@+id/GridLayout1"



android:columnCount="4"

android:useDefaultMargins="true" >

<TextView

android:layout_column="0"

android:layout_columnSpan="3"

android:layout_gravity="center_horizontal"

android:layout_marginTop="40dp"

android:layout_row="0"

android:text="User Credentials"

android:textSize="32dip" />

<TextView


android:layout_gravity="right"


android:text="User Name: " >

</TextView>

<EditText

android:id="@+id/input1"




android:ems="10" />

<TextView


android:layout_gravity="right"


android:text="Password: " >

</TextView>

<EditText

android:id="@+id/input1"




android:ems="8" />

<Button

android:id="@+id/button1"



android:text="Login" />

</GridLayout>

Run your example. You should see a nice arranged layout.

This is a layout example wherefore we have not connected any functionality to it. To

extend this example you could now connect the Button with a method in

the Activity via its android:onClick.

16. ScrollView

ScrollViews can be used to contain one view that might be to big to fit on one screen. If

the view is to big the ScrollView will display a scroll bar to scroll the context. Of course

this view can be a layout which can then contain other elements.

Create an android project "de.vogella.android.scrollview" with the activity "ScrollView".

Create the following layout and class.


<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"



android:fillViewport="true"


<LinearLayout

android:id="@+id/LinearLayout01"




<TextView

android:id="@+id/TextView01"



android:paddingLeft="8dip"

android:paddingRight="8dip"

android:paddingTop="8dip"

android:text="This is a header"

android:textAppearance="?android:attr/textAppearanceLarge" >

</TextView>

<TextView

android:id="@+id/TextView02"



android:layout_weight="1.0"

android:text="@+id/TextView02" >

</TextView>

<LinearLayout

android:id="@+id/LinearLayout02"


android:layout_height="wrap_content" >

<Button





android:text="Submit" >

</Button>

<Button





android:text="Cancel" >

</Button>

</LinearLayout>

</LinearLayout>

</ScrollView>

package de.vogella.android.scrollview;




import android.widget.TextView;

public class ScrollView extends Activity {

/** Called when the activity is first created. */

@Override




TextView view = (TextView) findViewById(R.id.TextView02);

String s="";

for (int i=0; i < 100; i++) {

s += "vogella.de ";

}

view.setText(s);

}

}

The attribute "android:fillViewport="true"" ensures that the scrollview is set to the full

screen even if the elements are smaller then one screen and the "layout_weight" tell the

android system that these elements should be extended.

17. Fragments

17.1. Overview

Fragment components allow you to organize your application code so that it is easier to

support different sized devices.

Fragments are components with their own lifecycle and their own user interface. They

can be defined via layout files or via coding.

Fragments always run in the context of an Activity. If an Activity is stopped

its Fragments will also be stopped; if an Activity is destroyed its Fragments will also get

destroyed.

If a Fragment component is defined in an XML layout file, the android:name attribute

points to the Fragmentsclass.

The base class for Fragments is android.app.Fragment. For special purposes you can

also use more special classes, like ListFragment or DialogFragment.

The onCreateView() method is called by Android once the Fragment should create its

user interface. Here you can inflate an layout. The onStart() method is called once the Fragment gets visible.

Fragments can be dynamically added and removed from

an Activity via Fragment transactions. This will add the action to the history stack of

the Activity, i.e. this will allow to revert the Fragment changes in theActivity via the

back button.

17.2. When to use Fragments

Fragments make it easy to re-use components in different layouts, e.g. you can build

single-pane layouts for handsets (phones) and multi-pane layouts for tablets.

This is not limited to tablets; for example you can use Fragments also to support

different layout for landscape and portrait orientation. But as tablets offer significantly

more space you typically include more views into the layout andFragments makes that

easier.

The typical example is a list of items in an activity. On a tablet you see the details

immediately on the same screen on the right hand side if you click on item. On a

handset you jump to a new detail screen. The following discussion will assume that you

have two Fragments (main and detail) but you can also have more. We will also have

one main activity and one detailed activity. On a tablet the main activity contains

both Fragments in its layout, on a handheld it only contains the main fragment.

To check for an fragment you can use the FragmentManager.

DetailFragment fragment = (DetailFragment) getFragmentManager().

findFragmentById(R.id.detail_frag);

if (fragment==null || ! fragment.isInLayout()) {

// start new Activity

}

else {

fragment.update(...);

}

To create different layouts with Fragments you can:

Use one activity, which displays two Fragments for tablets and only one on

handsets devices. In this case you would switch the Fragments in the activity

whenever necessary. This requires that the fragment is not declared in the layout

file as such Fragments cannot be removed during runtime. It also requires an

update of the action bar if the action bar status depends on the fragment.

Use separate activities to host each fragment on a handset. For example, when

the tablet UI uses twoFragments in an activity, use the same activity for handsets,

but supply an alternative layout that includes just one fragment. When you need

to switch Fragments, start another activity that hosts the other fragment.

The second approach is the most flexible and in general preferable way of

using Fragments. In this case the main activity checks if the detail fragment is available

in the layout. If the detailed fragment is there, the main activity tells the fragment that is

should update itself. If the detail fragment is not available the main activity starts the

detailed activity.

It is good practice that Fragments do not manipulate each other. For this purpose

a Fragment typically implements an interface to get new data from its host Activity.

18. Fragments Tutorial

18.1. Overview

The following tutorial demonstrates how to use Fragments. The

entry Activity (called MainActivity of our application ) will use different layouts for

portrait and for landscape mode.

In portrait mode MainActivity will show one Fragment with a list of names. If the user

touches an item in the list, a second Activity called DetailActivity will start and show

the selected text.

In landscape mode MainActivity will show two Fragments. The first is again

the Fragments which shows the list of names. The second Fragment shows the text of

the current selected item. This is similar to the portrait mode, but the whole information

will be shown on one screen.

18.2. Create project

Create a new project de.vogella.android.fragments with

an Activity called MainActivity.

18.3. Create layouts for landscape mode

Create or change the following layout files in the "res/layout/" folder.

First create the following file called "details.xml". This layout will be used by

the DetailFragment.






<TextView

android:id="@+id/detailsText"



android:layout_gravity="center_horizontal|center_vertical"

android:layout_marginTop="20dip"

android:text="Large Text"

android:textAppearance="?android:attr/textAppearanceLarge"

android:textSize="30dip" />

</LinearLayout>

Change the existing "main.xml" file. This layout will be used by MainActivity in

landscape mode and shows twoFragments.





android:orientation="horizontal" >

<fragment

android:id="@+id/listFragment"

android:layout_width="150dip"


android:layout_marginTop="?android:attr/actionBarSize"

class="de.vogella.android.fragments.ListFragment" ></fragment>

<fragment

android:id="@+id/detailFragment"



class="de.vogella.android.fragments.DetailFragment" >



</fragment>

</LinearLayout>

18.4. Create Fragment classes

Create now the Fragment classes. Create the ListFragment class.

package de.vogella.android.fragments;

import android.content.Intent;



import android.widget.ArrayAdapter;

import android.widget.ListView;

public class ListFragment extends android.app.ListFragment {

@Override



}

@Override

public void onActivityCreated(Bundle savedInstanceState) {

super.onActivityCreated(savedInstanceState);

String[] values = new String[] { "Android", "iPhone", "WindowsMobile",

"Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",

"Linux", "OS/2" };

ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),

android.R.layout.simple_list_item_1, values);

setListAdapter(adapter);

}

@Override

public void onListItemClick(ListView l, View v, int position, long id) {

String item = (String) getListAdapter().getItem(position);

DetailFragment fragment = (DetailFragment) getFragmentManager()

.findFragmentById(R.id.detailFragment);

if (fragment != null && fragment.isInLayout()) {

fragment.setText(item);

} else {

Intent intent = new Intent(getActivity().getApplicationContext(),

DetailActivity.class);

intent.putExtra("value", item);

startActivity(intent);

}

}

}

Create the DetailFragment class.


import android.app.Fragment;


import android.util.Log;

import android.view.LayoutInflater;


import android.view.ViewGroup;


public class DetailFragment extends Fragment {

@Override



Log.e("Test", "hello");

}

@Override

public void onActivityCreated(Bundle savedInstanceState) {

super.onActivityCreated(savedInstanceState);

}

@Override

public View onCreateView(LayoutInflater inflater, ViewGroup container,

Bundle savedInstanceState) {

View view = inflater.inflate(R.layout.details, container, false);

return view;

}

public void setText(String item) {

TextView view = (TextView) getView().findViewById(R.id.detailsText);

view.setText(item);

}

}

18.5. Create layouts for landscape mode

We want that Android uses a different main.xml file in portrait model then in landscape

mode.

For this reason create the "res/layout-port" folder.

In portrait mode Android will check the "layout-port" folder for fitting layout files. Only if

we would not have a "main.xml" file in "layout-port", Android would check the "layout"

folder.

Therefore create the following "main.mxl" layout file in "res/layout-port".





android:orientation="horizontal" >

<fragment

android:id="@+id/listFragment"



android:layout_marginTop="?android:attr/actionBarSize"

class="de.vogella.android.fragments.ListFragment" />

</LinearLayout>

Also create the "details_activity_layout.xml" layout file. This layout will be used in

the DetailActivity which is only used in portrait mode. Please note that we could have

create this file also in the "layout" folder, but as it is only used in portrait mode it is best

practise to place it into this folder.






<fragment

android:id="@+id/detailFragment"



class="de.vogella.android.fragments.DetailFragment" />

</LinearLayout>

18.6. Activities

Create a new Activity called DetailActivity with the following class.





public class DetailActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {


setContentView(R.layout.details_activity_layout);

Bundle extras = getIntent().getExtras();

if (extras != null) {

String s = extras.getString("value");

TextView view = (TextView) findViewById(R.id.detailsText);

view.setText(s);

}

}

}

MainActivity will remain unmodified.




public class MainActivity extends Activity {

/** Called when the activity is first created. */

@Override




}

}

18.7. Run

Run your example. If you run the application in portrait mode you should see only

one Fragment. Use Ctrl+F11 to switch the orientation. In horizontal mode you should see

two Fragments. If you select an item in portrait mode a new Activity should get started

with the selected item. In horizontal mode your second Fragment should display the

select item.

19. DDMS perspective and important views

19.1. DDMS - Dalvik Debug Monitor Server

Eclipse provides a perspective for interacting with your Android (virtual) device and your

Android application program. Select Window → Open Perspective → Other → DDMS to

open this perspective. It includes severalViews which can also be used independently

and allows for example the application to place calls and send SMS to the device. It

also allows the application to set the current geo position and allows you to perform a

performance trace of your application.

19.2. LogCat View

You can see the log (including System.out.print() statements) via the LogCat view.

19.3. File explorer

The file explorer allows to see the files on the Android simulator.

20. Shell

20.1. Android Debugging Bridge - Shell

You can access your Android emulator also via the console. Open a shell, switch to

your "android-sdk" installation directory into the folder "tools". Start the shell via the

following command "adb shell".

adb shell

You can also copy a file from and to your device via the following commands.

// Assume the gesture file exists on your Android device

adb pull /sdcard/gestures ~/test

// Now copy it back

adb push ~/test/gesture /sdcard/gestures2

This will connect you to your device and give you Linux command line access to the

underlying file system, e.g. ls, rm, mkdir, etc. The application data is stored in the

directory "/data/data/package_of_your_app".

If you have several devices running you can issue commands to one individual device.

# Lists all devices

adb devices

#Result

List of devices attached

emulator-5554 attached

emulator-5555 attached

# Issue a command to a specific device

adb -s emulator-5554 shell

20.2. Uninstall an application via adb

You can uninstall an android application via the shell. Switch the data/app directory

(cd /data/app) and simply delete your android application.

You can also uninstall an app via adb with the package name.

adb uninstall <packagename>

20.3. Emulator Console via telnet

Alternatively to adb you can also use telnet to connect to the device. This allows you to

simulate certain things, e.g. incoming call, change the network "stability", set your

current geocodes, etc. Use "telnet localhost 5554" to connect to your simulated device.

To exit the console session, use the command "quit" or "exit".

For example to change the power settings of your phone, to receive an sms and to get

an incoming call make the following.

# connects to device

telnet localhost 5554

# set the power level

power status full

power status charging

# make a call to the device

gsm call 012041293123

# send a sms to the device

sms send 12345 Will be home soon

# set the geo location

geo fix 48 51

For more information on the emulator console please see Emulator Console manual

21. Deploy your application on a real device

Turn on "USB Debugging" on your device in the settings. Select in the settings

Applications > Development, then enable USB debugging. You also need to install the

driver for your mobile phone. For details please see Developing on a Device . Please

note that the Android version you are developing for must be the installed version on

your phone.

To select your phone, select the "Run Configurations", select "Manual" selection and

select your device.

22. Thank you

Please help me to support this article:

23. Questions and Discussion

http://flattr.com/thing/49772/Tutorials-for-Eclipse-Java-Android-and-Webprogramming

Before posting questions, please see the vogella FAQ. If you have questions or find an

error in this article please use the www.vogella.de Google Group. I have created a short

list how to create good questions which might also help you.

24. Links and Literature

24.1. Source Code

Source Code of Examples

24.2. Android Resources

Android 2 (German Book)

Android ListView and ListActivity

Android SQlite Database

Android Widgets

Android Live Wallpaper

Android Services

Android Location API and Google Maps

Android Intents

Android and Networking

Android Homepage

Android Developer Homepage

Android Issues / Bugs

Android Google Groups

Android Live Folder

24.3. vogella Resources

Eclipse RCP Training (German) Eclipse RCP Training with Lars Vogel

Android Tutorial Introduction to Android Programming

GWT Tutorial Program in Java and compile to JavaScript and HTML

Eclipse RCP Tutorial Create native applications in Java

JUnit Tutorial Test your application

Git Tutorial Put everything you have under distributed version control system

Documents

Android Development Tutorial