Android - Apppcation Components

Apppcation components are the essential building blocks of an Android apppcation. These components are loosely coupled by the apppcation manifest file AndroidManifest.xml that describes each component of the apppcation and how they interact.

There are following four main components that can be used within an Android apppcation −

Activities

An activity represents a single screen with a user interface,in-short Activity performs actions on the screen. For example, an email apppcation might have one activity that shows a pst of new emails, another activity to compose an email, and another activity for reading emails. If an apppcation has more than one activity, then one of them should be marked as the activity that is presented when the apppcation is launched.

An activity is implemented as a subclass of Activity class as follows −

pubpc class MainActivity extends Activity {
}

Services

A service is a component that runs in the background to perform long-running operations. For example, a service might play music in the background while the user is in a different apppcation, or it might fetch data over the network without blocking user interaction with an activity.

A service is implemented as a subclass of Service class as follows −

pubpc class MyService extends Service {
}

Broadcast Receivers

Broadcast Receivers simply respond to broadcast messages from other apppcations or from the system. For example, apppcations can also initiate broadcasts to let other apppcations know that some data has been downloaded to the device and is available for them to use, so this is broadcast receiver who will intercept this communication and will initiate appropriate action.

A broadcast receiver is implemented as a subclass of BroadcastReceiver class and each message is broadcaster as an Intent object.

pubpc class MyReceiver  extends  BroadcastReceiver {
   pubpc void onReceive(context,intent){}
}

Content Providers

A content provider component supppes data from one apppcation to others on request. Such requests are handled by the methods of the ContentResolver class. The data may be stored in the file system, the database or somewhere else entirely.

A content provider is implemented as a subclass of ContentProvider class and must implement a standard set of APIs that enable other apppcations to perform transactions.

pubpc class MyContentProvider extends  ContentProvider {
   pubpc void onCreate(){}
}

We will go through these tags in detail while covering apppcation components in inspanidual chapters.

Additional Components

There are additional components which will be used in the construction of above mentioned entities, their logic, and wiring between them. These components are −