Broadcast Receivers

Broadcast Receivers in Android

A Broadcast Receiver is a component in Android used to listen for system-wide or app-specific broadcast messages (or events). These messages can be sent by the system (e.g., when the device boots) or by an application.

Types of Broadcasts

1. System Broadcasts: Sent by the Android system (e.g., battery level changes, connectivity changes, or incoming calls).
2. Custom Broadcasts: Sent by applications to communicate events within the app or to other apps.

How Broadcast Receivers Work

• Intent: Broadcast messages are sent using an Intent.
• Receiver: A Broadcast Receiver listens for these intents and executes code when the intent is received.

Declaring a Broadcast Receiver

1. Static Receiver (Manifest Declaration)
   Used for system-wide broadcasts or events. Declared in the AndroidManifest.xml.
2. Dynamic Receiver (Code Registration)
   Registered at runtime, often used for app-specific needs. Declared using Context.registerReceiver.

Steps to Implement a Broadcast Receiver

1. Create the Receiver Class

class MyBroadcastReceiver : BroadcastReceiver() {
    override fun onReceive(context: Context?, intent: Intent?) {
        // Handle the broadcast
        if (intent?.action == Intent.ACTION_BOOT_COMPLETED) {
            Toast.makeText(context, "Device Booted", Toast.LENGTH_SHORT).show()
        }
    }
}

2. Static Registration in Manifest

<receiver android:name=".MyBroadcastReceiver">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED" />
    </intent-filter>
</receiver>

• Add the required permission in the manifest:

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

3. Dynamic Registration

class MainActivity : AppCompatActivity() {

    private lateinit var myReceiver: MyBroadcastReceiver

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        myReceiver = MyBroadcastReceiver()

        // Register the receiver dynamically
        val intentFilter = IntentFilter().apply {
            addAction(Intent.ACTION_AIRPLANE_MODE_CHANGED)
        }
        registerReceiver(myReceiver, intentFilter)
    }

    override fun onDestroy() {
        super.onDestroy()
        // Unregister the receiver
        unregisterReceiver(myReceiver)
    }
}

Broadcast Sending

To send a custom broadcast:

Send a Broadcast

val intent = Intent("com.example.MY_CUSTOM_ACTION")
intent.putExtra("key", "value")
sendBroadcast(intent)

Receive a Custom Broadcast

Add a filter for the custom action in your receiver:

val intentFilter = IntentFilter("com.example.MY_CUSTOM_ACTION")
registerReceiver(myReceiver, intentFilter)

Common System Broadcast Actions

Best Practices

1. Static vs Dynamic Registration: Use static registration for system-level events and dynamic registration for app-specific needs.
2. Security: Restrict broadcasts using permissions to prevent misuse by other apps.
3. Performance: Avoid long-running operations in onReceive as it runs on the main thread. Use a service if needed.