What is BroadcastReceiver in Android?

This is a component that responds to system or user broadcast messages. It has no user interface and is designed to perform background operations in response to specific events.

Main characteristics:

• Responds to Intents with a specific action.
• Short-lived component, its onReceive() method executes for a brief period.
• Not intended for long operations. If long-running work is needed, a Service should be started from onReceive().
• Can be registered statically in the manifest or dynamically in code.

Examples of usage:

• Responding to network state changes (android.net.conn.CONNECTIVITY_CHANGE).
• Responding to system boot (android.intent.action.BOOT_COMPLETED).
• Handling incoming SMS.
• Receiving custom messages sent by other components or applications.

Registration in the manifest:

<receiver android:name=".MyBroadcastReceiver"
          android:exported="true"> // exported="true" so other apps can send intents
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED"/>
    </intent-filter>
</receiver>

Registration in code:

// In Activity or Service
IntentFilter filter = new IntentFilter("com.example.MY_CUSTOM_ACTION");
MyBroadcastReceiver receiver = new MyBroadcastReceiver();
registerReceiver(receiver, filter);

// In onDestroy() or onStop() - it's important to unregister!
unregisterReceiver(receiver);

BroadcastReceiver class:

public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // Code executed upon receiving an Intent
        // For example:
        if ("com.example.MY_CUSTOM_ACTION".equals(intent.getAction())) {
            Toast.makeText(context, "Received custom action!", Toast.LENGTH_SHORT).show();
        }
    }
}