Synapseindia android apps introduction hello world

1
Android Introduction
Hello World

Tutorial
 http://developer.android.com/resources/t
utorials/hello-world.html
 http://mobiforge.com/developing/story/ge
tting-started-with-android-development?
dm_switcher=true
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Create a New Android Project
 From Eclipse, select File > New > Android
Project.
 Fill in the project details with the following
values:
 Project name: HelloAndroid
 Application name: Hello, Android
 Package name: com.example.helloandroid (or
your own private namespace)
 Create Activity: HelloAndroid
Click Finish
3

4
Create a New
Android Project

Create a New Android Project
 Project name - the name of the project
 Package name - the name of the package. This
name will be used as the package name in your
Java files. Package name must be fully qualified.
The convention is to use your company's domain
name in reverse order
 Activity name - the name of the activity in your
Android application. In Android, think of an
activity as a screen containing some actions,
hence the name "activity"
 Application name - the user-friendly name of the
application that will be displayed in the
Applications tab of the Android UI
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Package Content
All source code here Java code for our activity
Generated Java code
Helps link resources to
Java code
Layout of the activity
Strings used in the
program
All non-code
resources
Android Manifest
Images

the various fields when create a new
Android project
 First, the src folder contains your Java source files. The HelloAndroid.java
file is the source file for the HelloAndroid activity you specified when you
created the project earlier.
 The R.java file is a special file generated by the ADT to keep track of all
the names of views, constants, etc, used in your Android project. You
should not modify the content of this file as its content is generated
automatically by the ADT.
 The Android Library contains a file named android.jar. This file contains all
the classes that you would use to program an Android application.
 The res folder contains all the resources used by your Android application.
For example, the drawable folder contains a png image file that is used as
the icon for your application. The layout folder contains an XML file used to
represent the user interface of your Android application. The values folder
contains an XML file used to store a list of string constants.
 The AndroidManifest.xml file is an application configuration file that
contains detailed information about your application, such as the number
of activities you have in your application, the types of permissions your
application needs, the version information of your application, and so on.
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8
Run the Application
 The Eclipse plugin makes it easy to run your applications:
 Select Run > Run.
 Select "Android Application".

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/res/layout/main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_height="wrap_content"
android:text="@string/hello"
/>
</LinearLayout>

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XML attributes
 xmlns:android
This is an XML namespace declaration that tells the Android
tools that you are going to refer to common attributes
defined in the Android namespace. The outermost tag in
every Android layout file must have this attribute.
 android:id
This attribute assigns a unique identifier to the TextView
element. You can use the assigned ID to reference this
View from your source code or from other XML resource
declarations.
 android:layout_width
This attribute defines how much of the available width on
the screen this View should consume. In this case, it's the
only View so you want it to take up the entire screen, which
is what a value of "fill_parent" means.

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XML attributes
 android:layout_height
This is just like android:layout_width, except that it refers
to available screen height.
 android:text
This sets the text that the TextView should display. In this
example, you use a string resource instead of a hard-coded
string value. The hello string is defined in the
res/values/strings.xml file. This is the recommended
practice for inserting strings to your application, because it
makes the localization of your application to other
languages graceful, without need to hard-code changes to
the layout file.

/res/values/strings.xml
 In Android, the UI of each activity is represented using various
objects known as Views. You can create a view using code, or
more simply through the use of an XML file.
 In this case, the UI Is represented using an XML file.
 The <TextView> element represents a text label on the screen
while the <LinearLayout> element specifies how views should be
arranged.
 Notice that the <TextView> element has an attribute named
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android:text with its value set to "@string/hello".
 The @string/hello refers to the string named hello defined in the
strings.xml file in the res/values folder.
<resources>
<string name="hello">Hello World, HelloAndroid!</string>
<string name="app_name">HelloAndroid</string>
</resources>

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Modify strings.xml
<resources>
<string name="hello">Hello, Android! I am a string
resource!</string>
<string name="app_name">Hello, Android</string>
</resources>

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Modify the main.xml
 Let's now modify the main.xml file. Add the following <Button> element:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_height="fill_parent"
>
<TextView
android:text="@string/hello"
/>
<Button
android:id="@+id/btnClickMe"
android:text="Click Me!"
/>
</LinearLayout>

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Construct UI
package com.example.helloandroid;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class HelloAndroid extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
tv.setText("Hello, Android");
setContentView(tv);
}
}

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R class
 In Eclipse, open the file named R.java (in the gen/ [Generated Java Files] folder).
 The R.java file is a special file generated by the ADT to keep track of all the names of
views, constants, etc, used in your Android project. You should not modify the
content of this file as its content is generated automatically by the ADT
package com.example.helloandroid;
public final class R {
public static final class attr {
}
public static final class drawable {
public static final int icon=0x7f020000;
}
public static final class id {
public static final int textview=0x7f050000;
}
public static final class layout {
public static final int main=0x7f030000;
}
public static final class string {
public static final int app_name=0x7f040001;
public static final int hello=0x7f040000;
}
}

AndroidManifest.xml
 The AndroidManifest.xml file is an application configuration file
that contains detailed information about your application, such as
the number of activities you have in your application, the types of
permissions your application needs, the version information of
your application, and so on.
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<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.helloandroid"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".HelloAndroid"
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>
</manifest>

Synapseindia android apps introduction hello world

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