Android Basics : Quick Start

First of all, basic question: How to learn Android?

1. “Google” it. (Sorry for the foul language =p)
2. API & book references.
• http://developer.android.com/reference/packages.html
3. Ask experienced people.
4. Think yourself.
5. Ask in forum or send email.
• http://developer.android.com/community/index.html

Ok. Lets continue...

There are 4 basic components in Android application.

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Activity Life-cycle

1. Activity

• Displays a user interface component and respond to system/user initiated.
• An Application may contain one or more Activities. One Activity is then considered as the main entry point by the system.
• Each Activity can be invoked from other Applications/Activities.
• Example:

public class Activity extends ApplicationContext {
   protected void onCreate(Bundle savedState);

   protected void onStart();
   protected void onRestart();
   protected void onResume();
   protected void onPause();
   protected void onStop();
   protected void onDestroy();
}
public class MyActivity extends Activity {}

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Different Layout View

2. View

• The basic building block for user interface components and creation of interactive UI components (buttons, text fields, etc.).
• Occupies a rectangular area on the screen and is responsible for drawing and event handling (scroll, tap, etc.).

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3. Service

• An application component that runs in the background, not interacting with the user, for an indefinite period of time.
• Two modes: a long-running service whose lifecycle is independent of the activity that started it; a service bound by other services and activities by its AIDL interface.
• Example:

public class MyService extends Service {
   public void onCreate();
   public void onDestroy();
   private final IService.Stub mBinder = new   IService.Stub() {
      //your service methods implementation
      Method1();
      Method2();
   }
 
   public IBinder onBind(Intent arg0) {
       return mBinder;
   }
}

Readings:
[1] http://www.androidcompetencycenter.com/2009/01/basics-of-android-part-iii-android-services/
[2] http://mylifewithandroid.blogspot.com/2008/02/double-life-of-service.html

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4. Intent

• An intent is an abstract description of an operation to be performed.
• Its most significant use is in the launching of Activities, where it can be thought of as the glue between Activities.
• It is a passive data structure holding an abstract description of an action to be performed.
• action
• data
• Usage
• Explicit passing: startActivity(Intent); startService(Intent)
• Broadcast: broadcastIntent – need to declare Intent Filter to receive the event.

Hope this article help those who just started in Android Development. :)

Read more at http://developer.android.com/guide/index.html.