Android App Dev 2

7/25/2019 Android App Dev 2

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Learn How to Develop Android

Application

Shakeel Iqbal,31 Jul 2013CPOL

4.81 (88 votes)

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This Article gives a basic concept for developing Android app.

Download HelloWorld.zip - 881.5 KB

Introduction
http://www.codeproject.com/script/Membership/View.aspx?mid=578505http://www.codeproject.com/script/Membership/View.aspx?mid=578505http://www.codeproject.com/info/cpol10.aspxhttp://www.codeproject.com/info/cpol10.aspxhttp://www.codeproject.com/info/cpol10.aspxhttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/KB/android/628894/HelloWorld.ziphttp://www.codeproject.com/KB/android/628894/HelloWorld.ziphttp://www.codeproject.com/KB/android/628894/HelloWorld.ziphttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/Articles/628894/Learn-How-to-Develop-Android-Applicationhttp://www.codeproject.com/info/cpol10.aspxhttp://www.codeproject.com/script/Membership/View.aspx?mid=578505


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These days the demand of smart phone is being increased and we have different types of

client e.g. Touch Phone, tables, Note etc. The demands of the applications for these smart

clients are constantly increasing and we have several operating systems for these smart

clients e.g. Android, IOS and Windows etc. This article will provide a guideline to .net

developer or beginners to develop Android Application.

Development Environment

This Article is not focusing on how to install/Configure development environment, you can

find different development environment on internet. In this article, I will use eclipse mobile

juno development environment.

Create New Project

For creating new project click on the File -> New -> Project.

It opens the new wizard window where you can select application template and set the

name of the project and package name.


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On the click on Next Button, it moves to the next step. Here provide the Application

Name, Project Name and Package Name. Package Name is a same as Name Space

in .Net and it must be unique. The project name is only used by Eclipse and it must be

unique in the workspace.


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You also need to select Minimum Required SDK from dropdown. It is the lowest version

of Android that your application will support. Then select Target SDK which is the HighestAPI that the application is known to work with. Then select the installed SDK for Compile

With option to compile your code for selected targeted SDK.

In the next steps of the wizard, you need to select icons, some other information and on

the last step provide the name of your activity and it's Navigation Type.


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I will provide the detail of activity and layout later, for now you can say it is windows formas desktop application or as a Web page in web application. Provide the name of Activity

and Layout. Leave Navigation type None for now. Press finish button. Eclipse will

automatically generate start up activity for you.


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Within the Eclipse, you can see your project in the Package Explorer pane of the left-hand

side of the screen. The HelloWorld application contains several auto generated folders and

file. Lets discuss it one by one.

/Src:It contains the all java source files those are associated to the project. For

example the MainActivity.java file generated by Eclipse is stored in this directory

under the package name com.MyFirst.helloworld you specified in the wizard. You

can add more packages for your application e.g. com.MyFirst.Fragments,

CommonClasses etc.

/gen:It contains the java source files and other code files generated by Eclipse. We

will use R.java file code later in our project. This file is generated to link your


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resource files for use in your java files in /src folder.

Andriod Directories (/Android 4.2 and /Android Dependencies):The Android 4.2

directory is generated against your selected Android SDK and Dependencies folder

the support file is generated for the backward compatibility with previous versions of

Android SDK.

/assests:By default this is empty folder, but you can put your raw assets in it and

these files include in your projects as-is. For Example it is good location for textures

and game data.

/bin:It is the output directory for build. You can find the final .apk file and other

compiled resources in this folder.

/libs:It contains the private libraries (jar) those you might want to use in your

application.

/res:It contains all the resources files those are associated to your application. All

the graphical element, string and layout of application exists one of the sub folder of

the res. We will add some resource later in this project. The auto generated layout

file activity_main.xml by Eclipse exists in layout sub folder.

Project.properties:This file is generated by android project wizard and it is used for

Eclipse settings. It is very rare to change this file directly. Instead Right click on the

project in Eclipse and click on properties and make any change which is required

for your application.

Run Your Application in Emulator

First you need to configure emulator for testing your application. To configure your emulator

click on window -> Android Virtual Device Manager


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It will open pop up where you can create new Virtual device, Edit exist and start any virtual

device. After create your new virtual device close this window. Now right click on theapplication in Package Explorer pane on the left-hand side of the screen and click on Run

As -> Android Application. It will compile your application and execute it in the emulator.


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After a few minutes the emulator will be started and you will be able to see your

HelloWorld application in it.

On the screen you can see Status Bar, Action Bar and Navigation Bar. You have nothing

to do with the Status Bar and Navigation Bar, it is being managed by System. The Action

bar contains the logo and title of your application and you can also open menu by click

Menu button (three vertical dots) on it. Layout Area where we place all UI controls.

Design Layout

As it is mentioned earlier Eclipse generates by default one layout. In emulator the

application is showing only Hello World! text in the middle of the screen. Open the layout

from /res/layout/activity_main.xml and you can see the layout in designer in the middle area

Eclipse. You can change view from graphic or xml as per your wish. Eclipse provides you

both option in the bottom of the layout Graphical Layout or activity_main.xml.


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In the designer you can see all available controls for UI design in different tabs e.g. Text

Fields, Layouts etc. I will create a UI given below in image for understanding the basic

component of Android application. Lets start playing with the layout.


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This layout is designed using Linear Layout. LinearLayout is a view group that aligns

children in single direction, Horizontal or Vertical. The attribute android:orientation is used to

set the direction. E.g. android:orientation="vertical". Eclipse provides a Property Pan on the

right-hand side of the screen to set the properties from designer. TextView control is a

readonly text. You can only view it and cannot edit it. EditText control is use for getting

input from the user. Button is a standard button control and on the click event we perform

action accordingly.

Hide Shrink Copy Code


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android:textStyle="bold" />


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android:layout_height="wrap_content"

android:text="@string/open_activity_title" />

.

.

.

One thing you must notice in this UI, I havent registered any event for the buttons here in

layout. We can do here using onClick attribute, but it is not a good way to do here. Now itis time to understand the some properties/attributes of different UI elements.

Properties

layout_width & layout_height:These properties are used for setting the width and height of

the element. The possible values are fill_parent, match_parent, wrap_content and any

number (e.g. 100dp). The fill_parent and match_parent are same. fill_parent is renamed to

match_parent in API level 8 and higher, which means that the view want to as big as

parent (minus padding). wrap_content means set the width or height according to the

content or child.

android:background="@drawable/header_bg_royal": This property is similar to the other

programming languages to set background of the element. The interesting point here is to

set the background from the resources of the android application. The header_bg_royal is

the image which I pasted in the res/drawable-hdpi. You can see complete path in the image

below.


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In layout xml file we can access resources using @ sign at the start of resource name.

@drawable means get the resource from the drawable folder. You can see more than one

drawable folders e.g. drawable-hdpi, drawable-ldpi etc. The reason for multiple folders is we

have large verity of client machine some is using tables, Note, mobiles etc. The screen size

and resolution varies client to client. You can create your icons, image for differentresolution and put it into the appropriate folder. Android OS will automatically pick best

suitable image for displaying. @drawable/header_bg_royal means get header_bg_royal

image/resource from drawable.

android:text="@string/intent_title": I hope you have understood what purpose of @ sign is

and what does string means after it and what intent_title is. Before explaining it again, let

me explain why I need to put all my strings in the resource files. If I hard code the text of

any control in xml file, the Eclipse gives warning to move it into the resource file. You can

see warning in the image given below, when I set the button text property is Button,Eclipse is giving warning message to move it into the string resource file.

The question is why it should be string resource. Although you can hardcode it, but it is not

a good programming practice. Suppose you have 10 occurrence of text in different activities

or layout. For changing that text you need to go into each activity/layout and change there.

If you put that text in the string resources then the change require only one place. You can

also create your application multilingual using these resource files.

@string/intent_title means get the value of intent_title from the string resource.

android:textColor="@color/white_color": For setting the fore color of the text, get color valuefrom resource file. In next section you will get to know how can we add value in resource

file.

android:id="@+id/btn_phone_call": If you want to access any control in code, assign it an

id. The + sign with @ means if the resource exist then use it otherwise create it.

@+id/btn_phone_call mean use the btn_phone_call in id resource and if it does exists then

create it.

Resource File


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Eclipse provides you a provision to add resources using designer. You can also use xml

view to add resources. You can add different type of resources e.g. string, color, array etc.

I will not go in the detail of resources in this article. You can read more about it in differenttutorials.

Activity

It is a most important concept of Android development. An activity represents the screen in

an application. You can use it in different ways as floating window or embedded inside of

another activity etc. The class must be inherited from Activity class for your activity. extends

keyword is used for inheritance in java.

Hide Copy Code

public class MainActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}


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@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.activity_main, menu);

return true;}

}

onCreate method is used to initialize your activity. We usually call setContentView() method

to define the layout for the activity and also get UI controls using findViewByid() that are

required to interact programmatically.

super.onCreate() means call the onCreate method of base class. Super is used to access

the base class in java. The layout that is associated with this activity is in

activity_main.xml . You can get the id of that resource using R.layout.activity_main. R is the

auto generated class that maintains the resources and we use it to access to resources in

code. setContentView(R.layout.activity_main) sets the layout for activity.

onCreateOptionsMenu() method is used to handle the menu for that activity. I will explain it

later.

Access Control/View in Activity

After setting the content view of the activity, you can get control using findViewById(viewId)

method. It takes the view/control id as a parameter and returns the view that is found. View

is the base class for widgets, which are used to create interactive UI components (buttons,

text fields, etc.). We need to cast the view into the original widgets.

Hide Copy Code

Button btnPhoneCall = (Button)findViewById(R.id.btn_phone_call);

EditText txtName = (EditText)findViewById(R.id.txt_name);

In above sample code findViewById(R.id.btn_phone_call) finds the button having id passed

as parameter and finds the


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@Override

public void onClick(View v) {

onPhoneCallClick();

}

});

There are three ways to implement listeners in java and they have their own advantages

and disadvantages. These three ways are

Inline implementation

Using the implements keyword

By using variables

You can study about these different ways on the internet. In the above example I register

listener for button using Inline implementation. Call setOnClickListener() method of button

and pass OnClickListener as an parameter. In OnClickListener handler override the onClick

event. When user will click on button, it will call onClick event. You can write your code

inside onClick.

Intent

Intent is the asynchronous message which allows android components to request

functionality from the other component of the Android System. It represents an apps Intent

to do something. We can use intents for different tasks e.g. making call, open map, open

activity etc. But most often they are used to start another activity.

How to Start another Activity

Till here, you have learnt about activity, layout resources and intent. Create another activity

name LifeCycleActivity and create its layout activity_life_cycle.xml in layout folder. It is

better to use Eclipse to add activity in your application that automatically generates layout

for that activity and automatically put necessary information of activity in

AndroidManifest.xml file. Otherwise you need to do it manually. Right click on your

application in Package Explorer pane in left-hand side and click on New > Other. It will

open a popup window where you need to select Android Activity and after completing the

wizard, it will create a Activity and default layout for you.


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Create object of Intent class and pass it to the startActivity() method. Intent class has

different type of constructor, for starting activity pass context and activity class to the object.

Activity class is the subclass of context, so pass this as a first parameter and the pass the

class as to which the system should deliver the intent. Then pass this intent to the

startActivity() method and your second activity will be started.

Hide Copy Code

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

startActivity(intent);

There are some other methods for starting activity. You can study about them too.

startActivityForResult(intent, requestCode)

startActivityFromChild(child, intent, requestCode)

startActivityFromFragment(fragment, intent, requestCode)

Open Phone Dialer

Launching the Phone dialer is also quite easy in Android you can send message to Android

OS to run specific application using intent

Hide Copy Code

Uri uri = Uri.parse("tel:03361122334");

Intent intent = new Intent(Intent.ACTION_VIEW,uri);


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@Override

protected void onCreate(Bundle savedInstanceState) {

}

@Override

protected void onStart() {

}

@Override

protected void onRestart() {

}

@Override

protected void onResume() {

}

@Override

protected void onPause() {

}

@Override

protected void onStop() {

}

@Override

protected void onDestroy() {

}

onCreate() method called when activity is first created. onStart() called when activity is

visible to user and onResume() called when application starts interaction with the user. At

this point your activity comes at the top of activity stack.


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onPause() method called when system is about to start resuming of previous activity. It is

typically used to save the unsaved data to persist it, stop animation or other work that can

consume CPU.

onStop() method called when the activity is no longer visible to the user, because anotheractivity has been resumed and is covering this one.

onRestart() called after your activity has been stopped. It called prior to being started again.

onDestroy() called before your activity is destroyed.

Create Menu

For creating menu, open the res/menu/activity_main.xml file and add your menu items in it.

Set id and title for each menu item and then you can handle this menu item by id in

activity class.

Hide Copy Code


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android:id="@+id/menu_exit"

android:showAsAction="never"

android:title="@string/menu_exit"/>

For handling on click method of the menu item override theonOptionsItemSelected(MenuItem

item) method in your activity. This method fires whenever user click/select any menu item.

For handling different actions for each element get the id of the selected menu item using

getItemId() method and perform action for each menu item.


@Overridepublic boolean onOptionsItemSelected(MenuItem item) {

boolean handled = false;

int id = item.getItemId();

switch(id)

{

case R.id.menu_settings:{

Toast.makeText(this, "Clicked on setting menu item.",

Toast.LENGTH_SHORT).show();

handled = true;

break;

}

case R.id.menu_other:

{

onOpenActivity();

handled = true;

break;

}

case R.id.menu_exit:

{

finish();

handled = true;


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break;

}

default:

{

handled = super.onOptionsItemSelected(item);}

}

return handled;

}

Each activity can has its own menu. You can put different menu items for each activity andhandle it differently. Some activity cannot have any menu. For this dont override

onCreateOptionsMenu method in your activity. In this method we inflate menu items to

menuInflater.

License

This article, along with any associated source code and files, is licensed under The Code

Project Open License (CPOL)

Android Development For Beginners

Thank you for signing up for the course! We look forward to working with you and hearing

your feedback in our forums.

Need help getting started?

Find an answer to your question in theUdacity FAQ

Learn about different parts of the Classroom in Udacity Introduction

Contents

1Course Resourceso 1.1 Additional Documentation
http://www.codeproject.com/info/cpol10.aspxhttp://www.codeproject.com/info/cpol10.aspxhttps://www.udacity.com/faqhttps://www.udacity.com/faqhttps://www.udacity.com/wiki/udacityintroductionhttps://www.udacity.com/wiki/ud837#course-resourceshttps://www.udacity.com/wiki/ud837#course-resourceshttps://www.udacity.com/wiki/ud837#additional-documentationhttps://www.udacity.com/wiki/ud837#additional-documentationhttps://www.udacity.com/wiki/ud837#additional-documentationhttps://www.udacity.com/wiki/ud837#course-resourceshttps://www.udacity.com/wiki/udacityintroductionhttps://www.udacity.com/faqhttp://www.codeproject.com/info/cpol10.aspxhttp://www.codeproject.com/info/cpol10.aspx


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o 1.2 Downloadable Materials

2Course Syllabus

o 2.1 Lesson 1: Building Layouts

o 2.2 Lesson 2: Making an App Interactive

o

2.3 Lesson 3: Work with the Android Framework and Control Flow 3Acknowledgements

Course Resources

Additional Documentation

1. The Android XML Visualizer

2.

Common Android Views Cheat-sheet

3.

Java Data Types Cheat-Sheet

4. Layout Cheat-Sheet

5.

Vocabulary Words

6.

Android Developers Website

7. The Material Design Specification

Downloadable Materials

You can download Supplemental Materials, Lesson Videos and Transcripts from

Downloadables (bottom right corner of the Classroom) or from the Dashboard (first option

on the navigation bar on the left hand side).

The final code for the course is freely available in threeGithubrepositories. Github is a

website that facilitates sharing code online. Code on Github is organized via the Gitversion

control system. To learn more about Git and Github, consider taking ourversion control

course.

1.

Code forHappy Birthday

2. Code forJust Java

3.

Code forCourt Counter

Course Syllabus

Lesson 1: Building Layouts
https://www.udacity.com/wiki/ud837#downloadable-materialshttps://www.udacity.com/wiki/ud837#downloadable-materialshttps://www.udacity.com/wiki/ud837#course-syllabushttps://www.udacity.com/wiki/ud837#course-syllabushttps://www.udacity.com/wiki/ud837#course-syllabushttps://www.udacity.com/wiki/ud837#lesson-1-building-layoutshttps://www.udacity.com/wiki/ud837#lesson-1-building-layoutshttps://www.udacity.com/wiki/ud837#lesson-2-making-an-app-interactivehttps://www.udacity.com/wiki/ud837#lesson-3-work-with-the-android-framework-and-control-flowhttps://www.udacity.com/wiki/ud837#acknowledgementshttps://www.udacity.com/wiki/ud837#acknowledgementshttp://labs.udacity.com/android-visualizer/#/android/sandboxhttp://labs.udacity.com/android-visualizer/#/android/sandboxhttps://s3-us-west-1.amazonaws.com/udacity-content/PDFs/Common+Android+Views+Cheat+Sheet+%281%29.pdfhttps://s3-us-west-1.amazonaws.com/udacity-content/PDFs/Common+Android+Views+Cheat+Sheet+%281%29.pdfhttp://labs.udacity.com/images/Java-Data-Types-Cheat-Sheet.pdfhttp://labs.udacity.com/images/Java-Data-Types-Cheat-Sheet.pdfhttp://labs.udacity.com/images/Layout-Cheat-Sheet.pdfhttp://labs.udacity.com/images/Layout-Cheat-Sheet.pdfhttps://developers.google.com/android/for-all/vocab-words/https://developers.google.com/android/for-all/vocab-words/http://developer.android.com/index.htmlhttp://www.google.com/design/spec/material-design/introduction.htmlhttp://www.google.com/design/spec/material-design/introduction.htmlhttps://github.com/https://github.com/https://git-scm.com/https://git-scm.com/https://www.udacity.com/course/how-to-use-git-and-github--ud775https://www.udacity.com/course/how-to-use-git-and-github--ud775https://www.udacity.com/course/how-to-use-git-and-github--ud775https://www.udacity.com/course/how-to-use-git-and-github--ud775https://github.com/udacity/Happy-Birthdayhttps://github.com/udacity/Happy-Birthdayhttps://github.com/udacity/Happy-Birthdayhttps://github.com/udacity/Just-Javahttps://github.com/udacity/Just-Javahttps://github.com/udacity/Court-Counterhttps://github.com/udacity/Court-Counterhttps://github.com/udacity/Court-Counterhttps://github.com/udacity/Court-Counterhttps://github.com/udacity/Just-Javahttps://github.com/udacity/Happy-Birthdayhttps://www.udacity.com/course/how-to-use-git-and-github--ud775https://www.udacity.com/course/how-to-use-git-and-github--ud775https://git-scm.com/https://github.com/http://www.google.com/design/spec/material-design/introduction.htmlhttp://developer.android.com/index.htmlhttps://developers.google.com/android/for-all/vocab-words/http://labs.udacity.com/images/Layout-Cheat-Sheet.pdfhttp://labs.udacity.com/images/Java-Data-Types-Cheat-Sheet.pdfhttps://s3-us-west-1.amazonaws.com/udacity-content/PDFs/Common+Android+Views+Cheat+Sheet+%281%29.pdfhttp://labs.udacity.com/android-visualizer/#/android/sandboxhttps://www.udacity.com/wiki/ud837#acknowledgementshttps://www.udacity.com/wiki/ud837#lesson-3-work-with-the-android-framework-and-control-flowhttps://www.udacity.com/wiki/ud837#lesson-2-making-an-app-interactivehttps://www.udacity.com/wiki/ud837#lesson-1-building-layoutshttps://www.udacity.com/wiki/ud837#course-syllabushttps://www.udacity.com/wiki/ud837#downloadable-materials


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In this lesson you'll learn about various Views and ViewGroups used to make layouts for

your Android apps. Topics include:

Writing XML

TextViews and ImageViews Styling your views

Positioning your views with ViewGroups

LinearLayout weight

Using RelativeLayout to position views relative to each other

Following Lesson 1 is Practice Set 1, where you will:

DownloadAndroid Studio

Make a Hello World Application and run it on your phone

Create a Birthday Card Application

Create your own custom card and video for the Make Your Own Cardshowcase!

Lesson 2: Making an App Interactive
https://developer.android.com/sdk/index.htmlhttps://developer.android.com/sdk/index.htmlhttps://developer.android.com/sdk/index.htmlhttp://discussions.udacity.com/t/make-your-own-card/19643http://discussions.udacity.com/t/make-your-own-card/19643https://developer.android.com/sdk/index.html


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In this lesson you'll start learning Java by creating the JustJava coffee ordering app seen

below:

Topics include:

Making a button click execute code

Having the app evaluate math expressions

Declaring, initializing and using variables

Variable scope

Nested layouts

The String datatype

Combining Strings, ints and variables with concatenation

Following Lesson 2 is Practice Set 2, where you will:

Identify incorrect variable declarations and initializations

Determine program output

Determine whether variables should be local or global

Build the CourtCounter basketball scoring app seen below:


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Lesson 3: Work with the Android Framework and Control Flow

In this lesson you'll finish the JustJava coffee ordering app by adding more coffee ordering

options and nuanced control flow. You'll learn about object oriented programming so that

you can harness several features of the Android Framework. Topics include:

Method declaration and calling

Parameters and return values

An introduction to Object Oriented Programming

Changing the attributes of your views dynamically

Creating conditional logic using if/else statements

Following Lesson 3 is the course's final project 5 Things. For the final project you will

create an educational app that teaches the user five things. During this project you will:

Plan out your app design prior to coding, based on user feedback and needs

Take an app layout from drawing to XML code

Create, position, and style views


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Create interactivity through button clicks and Java code

Students enrolled in the class for pay can submit the final project for review. To learn more

about the final project, clickhere.
https://www.udacity.com/course/viewer#%21/c-ud837/l-4040108662/m-4606438835https://www.udacity.com/course/viewer#%21/c-ud837/l-4040108662/m-4606438835https://www.udacity.com/course/viewer#%21/c-ud837/l-4040108662/m-4606438835https://www.udacity.com/course/viewer#%21/c-ud837/l-4040108662/m-4606438835

Documents

Android App Dev 2