Broadcast Receivers

What is a Broadcast Receiver?

A broadcast receiver is an Android component that listens for system-wide or app-specific broadcast events. When a matching broadcast is sent, Android wakes up the receiver and delivers the intent.

Two Registration Methods

1. Manifest-declared receivers
Registered in AndroidManifest.xml. The system starts the receiver when the broadcast occurs, even if the app is not running.

<receiver
    android:name=".BootReceiver"
    android:enabled="true"
    android:exported="true">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED" />
    </intent-filter>
</receiver>

class BootReceiver : BroadcastReceiver() {
    override fun onReceive(context: Context, intent: Intent) {
        if (intent.action == Intent.ACTION_BOOT_COMPLETED) {
            // Schedule periodic work on boot
            WorkManager.getInstance(context)
                .enqueueUniqueWork(
                    "BootSync",
                    ExistingWorkPolicy.KEEP,
                    OneTimeWorkRequestBuilder<BootSyncWorker>().build()
                )
        }
    }
}

2. Runtime-registered receivers
Registered in code using registerReceiver(). Only active while the registering component is alive.

class NetworkActivity : AppCompatActivity() {
    private val networkReceiver = object : BroadcastReceiver() {
        override fun onReceive(context: Context, intent: Intent) {
            val isConnected = intent.getBooleanExtra(
                ConnectivityManager.EXTRA_NO_CONNECTIVITY, false
            )
            updateUI(isConnected)
        }
    }

    override fun onStart() {
        super.onStart()
        val filter = IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION)
        registerReceiver(networkReceiver, filter)
    }

    override fun onStop() {
        super.onStop()
        unregisterReceiver(networkReceiver)
    }
}

Key Differences

Android 8.0+ Restrictions

Android 8.0 removed most implicit broadcasts from manifest-declared receivers. Only a whitelist of broadcasts can still be declared in the manifest:

• ACTION_BOOT_COMPLETED
• ACTION_LOCALE_CHANGED
• ACTION_TIMEZONE_CHANGED
• ACTION_POWER_CONNECTED / ACTION_POWER_DISCONNECTED
• ACTION_SHUTDOWN

All other implicit broadcasts must be registered at runtime.

Common System Broadcasts

Exported Receivers

For Android 12+, explicitly set android:exported on all receivers:

<!-- Only your app can trigger this -->
<receiver
    android:name=".InternalReceiver"
    android:exported="false">
    <intent-filter>
        <action android:name="com.myapp.INTERNAL_ACTION" />
    </intent-filter>
</receiver>

<!-- External apps can trigger this -->
<receiver
    android:name=".BootReceiver"
    android:exported="true">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED" />
    </intent-filter>
</receiver>

Android 13+ Runtime Permission

For runtime receivers listening to ACTION_PACKAGE_ADDED, ACTION_PACKAGE_REMOVED, or similar package-related broadcasts, you need the QUERY_ALL_PACKAGES permission or a specific <queries> declaration in the manifest.

LocalBroadcastManager (Deprecated)

LocalBroadcastManager was used for app-internal broadcasts that never leave the process. It is deprecated because StateFlow/SharedFlow and LiveData are better alternatives:

// Old approach (deprecated)
LocalBroadcastManager.getInstance(context)
    .registerReceiver(receiver, IntentFilter("INTERNAL_EVENT"))

// Modern approach — use Flow
class EventBus {
    private val _events = MutableSharedFlow<Event>()
    val events: SharedFlow<Event> = _events

    suspend fun emit(event: Event) {
        _events.emit(event)
    }
}

Best Practices

1. Always unregister runtime receivers — unregister in onStop() or onDestroy() to avoid memory leaks.
2. Use exported=false — unless external apps must trigger the receiver.
3. Use explicit intents — for app-internal broadcasts, avoid implicit broadcasts that could be intercepted.
4. Check intent action — always verify intent.action before processing.
5. Prefer Flow over LocalBroadcastManager — for type-safe, lifecycle-aware communication.