03.ApplicationBasic

Android Basic Course

© 2012 University of Science – HCM City .

M.Sc. Bui Tan Loc

[email protected]

Department of Software Engineering,

Faculty of Information Technology,

University of Science – Ho Chi Minh City, Viet Nam

Module 3: Application Basic

mailto:[email protected]



Objectives

• After completing this module, you will have learned: • About project structure

• How resources are used

• How Different Resources Are Referenced from Within Java and XML Files

• Some main content of the AndroidManifest.xml file

• About Fundamental Android UI Design

• About XML-based layouts

• About Handling events by using event handlers or listeners

2



Contents

• Understanding project structure

• How different resources are referenced from within Java and XML Files

• The Android application manifest

• Fundamental Android UI Design

• Overview XML-based layouts

• Handling events by using event handlers

• Handling events by using event listeners

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Understanding project structure

contains java source files

is generated when res folder is modified

is selected platform to build the application

is application package that will be installed on emulators or real devices

are image resources

describes UI components

describes string constant values

is an application configuration file

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How Different Resources Are Referenced from Within Java and XML Files

Resource Reference in Java Reference in XML

res/layout/main.xml R.layout.main @layout/main

res/drawable-hdpi/icon.png R.drawable.icon @drawable/icon

@+id/home_button R.id.home_button @id/home_button

<string name = “hello”> R.string.hello @string/hello

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R.java file is generated by resources

6



Different resources are referenced from within Manifest file

7



Using R.java file

…

setContentView(R.layout.main); …

mTitleText = (EditText) findViewById(R.id.title); mBodyText = (EditText) findViewById(R.id.body);

…

8



The Android application manifest

• Each Android project includes a manifest file, AndroidManifest.xml, stored in the root of the project hierarchy. The manifest lets you define the structure and metadata of your application, its components, and its requirements.

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Android application components and declaring requirements

Java Base Class Functionality Examples

Activity Focus thing a user can do Edit a note, play a game

Service Background Process Play music, update weather icon

ContentProvider Store and retrieve data Open a phone contact

BroadcastReceiver Receive message Trigger alarm upon event

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• The Android Application Manifest file includes nodes for each of the components (Activities, Services, Content Providers, and Broadcast Receivers) that make up your application and, using Intent Filters and Permissions, determines how they interact with each other and with other applications.



Some main content of the AndroidManifest.xml

• Manifest Root document • Version Code Property

• Version Name Property

• Use-SDK Node •Min SDK Version

•Max SDK Version

• Target SDK Version

• Use-Permission Nodes

• Application Node •Activity Nodes

•Service Nodes

• Content Provider Nodes

• Broadcast Receiver Nodes

Using Intent Filters and Permissions

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The AndroidManifest.xml of Hello World Application

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

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

package="com.example.helloandroid"

android:versionCode="1"

android:versionName="1.0" >

<uses-sdk android:minSdkVersion="10" />

<application

android:icon="@drawable/ic_launcher"

android:label="@string/app_name" >

<activity

android:label="@string/app_name"

android:name=".HelloAndroid" >

<intent-filter >

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

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

</intent-filter>

</activity>

</application>

</manifest>

Each upload to Market requires versionCode increment

Specifies icon for launching app

Specifies icon for launching app

Specifies activity to be launched at startup

Using Intent Filters and Permission

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The AndroidManifest.xml of Contact Manager Application <?xml version="1.0" encoding="utf-8"?>


package="com.example.android.contactmanager"

android:versionCode="1" android:versionName="1.0">

<uses-sdk android:minSdkVersion="5" android:targetSdkVersion="5" />

<uses-permission android:name="android.permission.GET_ACCOUNTS" />

<uses-permission android:name="android.permission.READ_CONTACTS" />

<uses-permission android:name="android.permission.WRITE_CONTACTS" />

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

<activity android:name=".ContactManager" android:label="@string/app_name">

<intent-filter>

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

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

</intent-filter>

</activity>

<activity

android:name="ContactAdder"

android:label="@string/addContactTitle">

</activity>

</application>

</manifest>

Security permissions requested from user on install

Activity Node

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The AndroidManifest.xml of Note Pad Application



package="com.example.android.notepad" >

<uses-sdk android:minSdkVersion="11" />

<application

android:icon="@drawable/app_notes"

android:label="@string/app_name" >

<provider

android:authorities="com.google.provider.NotePad"

android:exported="false"

android:name="NotePadProvider" >

<grant-uri-permission android:pathPattern=".*" />

</provider>

<activity

…

</activity>

…

</application>

</manifest>

Content Provider Node

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The AndroidManifest.xml of Random Music Player Application

…

<application

…

<service

android:exported="false"

android:name=".MusicService" >

<intent-filter >

<action android:name="com.example.android.musicplayer.action.TOGGLE_PLAYBACK" />

<action android:name="com.example.android.musicplayer.action.PLAY" />

<action android:name="com.example.android.musicplayer.action.PAUSE" />

<action android:name="com.example.android.musicplayer.action.SKIP" />

<action android:name="com.example.android.musicplayer.action.REWIND" />

<action android:name="com.example.android.musicplayer.action.STOP" />

</intent-filter>

<intent-filter >

<action android:name="com.example.android.musicplayer.action.URL" />

<data android:scheme="http" />

</intent-filter>

</service>

…

Service Node

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The AndroidManifest.xml of Random Music Player Application

…

<receiver android:name=".MusicIntentReceiver" >

<intent-filter >

<action android:name="android.media.AUDIO_BECOMING_NOISY" />

</intent-filter>

<intent-filter >

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

</intent-filter>

</receiver>

…

</application>

… Broadcast Receiver Node

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Fundamental Android UI Design

• Views are the base class for all visual interface elements (commonly known as controls or widgets). All UI controls, including the layout classes, are derived from View.

• View Groups are extensions of the View class that can contain multiple child Views. Extend the ViewGroup class to create compound controls made up of interconnected child Views. The ViewGroup class is also extended to provide the layout managers that help you lay out controls within your Activities.

• Activities described in the previous modules, represent the window, or screen, being displayed. Activities are the Android equivalent of Forms. To display a user interface you assign a View (usually a layout) to an Activity.

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High-level diagram class of the Android View API

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View

ViewGroup

Activity

… …

… …

Android built-in layout classes

Android built-in view container classes

Android built-in single view classes



A part of a class diagram of the Android View API

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A subset of methods in the base Android View API

setBackgroundColor(int color)

setBackgroundDrawable(Drawable d)

setClickable(boolean c)

setFocusable(boolean f)

setLayoutParams(ViewGroup.LayoutParams l)

setMinimumHeight(int minHeight)

setMinimumWidth(int minWidth)

setOnClickListener(OnClickListener l)

setOnFocusChangeListener(OnFocusChangeListener l)

setPadding(int left, int right, int top, int bottom)

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Using XML-Based Layouts

•While it is technically possible to create and attach widgets to your activity purely through Java code, the more common approach is to use an XML-based layout file.

• Dynamic instantiation of widgets is reserved for more complicated scenarios, where the widgets are not known at compile time (e.g., populating a column of radio buttons based on data retrieved from the Internet)

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XML – based layout file is defined here



What Is an XML-Based Layout?

• An XML-based layout is a specification of widgets’ relationships to each other—and to containers—encoded in XML format.

• Android considers XML-based layouts to be resources, and as such, layout files are stored in the res/layout directory inside your Android project

• Each XML file contains a tree of elements specifying a layout of widgets and containers that make up one View. The attributes of the XML elements are properties, describing how a widget should look or how a container should behave.

• Android’s SDK ships with a tool (aapt) that uses the layouts. Of particular importance to you as a developer is that aapt generates the R.java source file within your project’s gen/ directory, allowing you to access layouts and widgets within those layouts directly from your Java code

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Why Use XML-Based Layouts?

• Most everything you do using XML layout files can be achieved through Java code. For example, you could use setTypeface() to have a button render its text in bold, instead of using a property in an XML layout.

• Dynamic instantiation of widgets is reserved for more complicated scenarios, where the widgets are not known at compile time.

• Using XML-based layout does have the advantage of helping to ease the transition to Android from any other XML-centered view description language. • Ex: XAML, Adobe’s Flex, GWT, XUI, etc.

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XLM-based layout example


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

android:id="@+id/button"

android:text=""

android:layout_width="fill_parent"

android:layout_height="fill_parent"/>

• The + after the @ in the id string indicates that the id should be automatically created as a resource if it does not already exist.

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Loading XML-based layout resources

package com.commonsware.android.layouts;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import java.util.Date;

public class NowRedux extends Activity

implements View.OnClickListener {

Button btn;

@Override

public void onCreate(Bundle icicle) {

super.onCreate(icicle);

setContentView(R.layout.main);

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

btn.setOnClickListener(this);

updateTime();

}

public void onClick(View view) {

updateTime();

}

private void updateTime() {

btn.setText(new Date().toString());

}

}

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<Button

…

android:id="@+id/button“

…

android:layout_height="fill_parent"/>



Handling events by using event handlers

public class ExampleActivity extends Activity implements OnClickListener { protected void onCreate(Bundle savedValues) { ... Button button = (Button)findViewById(R.id.corky); Button button = (Button)findViewById(R.id.sketchy); ... button.setOnClickListener(this); } // Implement the OnClickListener callback public void onClick(View v) { switch(v.getId()) { case R.id.corky: // do something when the button is clicked … case R.id.sketchy: // do something when the button is clicked … } } ... }

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Handling events by using event listeners

protected void onCreate(Bundle savedValues) {

...

// Capture our button from layout

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

// Register the onClick listener with the implementation above

button.setOnClickListener(new OnClickListener() { public void onClick(View v) {

// do something when the button is clicked

}

});

...

}

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// Create an anonymous implementation of OnClickListener

private OnClickListener mCorkyListener = new OnClickListener() {

public void onClick(View v) {

// do something when the button is clicked

}

};

protected void onCreate(Bundle savedValues) {

...

// Capture our button from layout

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

// Register the onClick listener with the implementation above

button.setOnClickListener(mCorkyListener);

...

}

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<Button

...

android:onClick="someMethod"

...

/>

public void someMethod(View theButton) {

// do something useful here

}

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Questions or Discussions

• How many kinds of resources are there in an Android Application? What are they?

• How are resources used?

•Why should we use string values in string.xml file rather than use them directly? • Ex:

•Should use tv.setText(R.string.app_name);

•Shouldn’t use tv.setText("Hello, Android");

•Why use xml-based layouts?

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References & Further Readings

• List of Files for an Android Application • http://developer.android.com/resources/faq/commontasks.html#fi

lelist

• Print Messages to a Log File • http://developer.android.com/resources/faq/commontasks.html#lo

gging

• Getting a Handle to a Screen Element • http://developer.android.com/resources/faq/commontasks.html#h

andle

• Listening for Button Clicks • http://developer.android.com/resources/faq/commontasks.html#li

stening

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http://developer.android.com/resources/faq/commontasks.html















































• The Android Developer’s Cookbook Building Applications with the Android SDK, James Steele, Nelson To, Addison-Wesley Professional Publishing (2011)

• Android Application Overview, Chapter 2

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References & Further readings

• Professional Android 2 Application Development, Reto Meier, Wiley Publishing (2010) • Fundamental Android UI Design,

Chapter 4

33




• Beginning Android 3, Mark Murphy, Apress Publishing (2011) • Using XML-Based Layouts,

Chapter 3

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03.ApplicationBasic

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