Broadcast Receivers

A BroadcastReceiver is an Android component that:
- Listens for broadcast messages (called Intents)
- Reacts to system-wide or app-wide events
- Does not have a UI

A broadcast is just an Intent sent out to multiple potential listeners.

Examples of events that trigger broadcasts:
- Device boot completed
- Battery low / battery okay
- Network connectivity changed
- SMS received
- Screen on / off
- App-specific events (your own custom broadcasts)

Android apps can send or receive broadcast messages from the Android system and other Android apps, similar to the publish-subscribe pattern.

Types of Broadcast Receivers

1. Manifest-declared (Static Receivers)

Declared in AndroidManifest.xml

<receiver
    android:name=".AirplaneModeChangeReceiver"
    android:exported="true">
    <intent-filter>
        <action android:name="android.intent.action.AIRPLANE_MODE"/>
    </intent-filter>
</receiver>

Used when:

You need to receive events even when the app is not running

Important Android reality check:

Since Android 8.0 (API 26), most implicit broadcasts cannot be registered in the manifest anymore.

Still allowed:

BOOT_COMPLETED
SMS_RECEIVED
Some system-critical broadcasts

2. Context-registered (Dynamic Receivers)

Registered at runtime using code.

Registering the Receiver:

// For connectivity change, use
IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);

 // For Airplane Mode
IntentFilter filter = new IntentFilter(Intent.ACTION_AIRPLANE_MODE_CHANGED);

registerReceiver(airplaneModeChangeReceiver, filter);

Broadcast Receiver:

public void onReceive(Context context, Intent intent) {

    if(intent.getAction() == ConnectivityManager.CONNECTIVITY_ACTION) {
        Log.d(TAG, "Connectivity Changed");
    }
    if(intent.getAction() == Intent.ACTION_AIRPLANE_MODE_CHANGED){
        // returns 1 when airplane mode is ON, otherwise returns 0
        int isTurnedOn = Settings.Global.getInt(context.getContentResolver(), Settings.Global.AIRPLANE_MODE_ON, 0);

        String status = ((isTurnedOn ==  1) ? "ON" : "OFF");
        Log.d(TAG, "Airplane Mode is " + status);
    }
}

Unregistering the Receiver:

unregisterReceiver(airplaneModeChangeReceiver);

Types of Broadcasts

System Broadcasts

Sent by Android OS.

Intent.ACTION_BATTERY_LOW
Intent.ACTION_BOOT_COMPLETED
Intent.ACTION_AIRPLANE_MODE_CHANGED

Custom Broadcasts

APP Sending Custom Broadcast:

Intent intent = new Intent();
intent.setAction("com.example.custombroadcast.ACTION_CUSTOM");
sendBroadcast(intent);

APP Receiving Custom Broadcast:

Registering the receiver:

CustomBroadcastReceiver customBroadcastReceiver = new CustomBroadcastReceiver();

IntentFilter filter = new IntentFilter();
filter.addAction("com.example.custombroadcast.ACTION_CUSTOM");

registerReceiver(customBroadcastReceiver, filter, Context.RECEIVER_EXPORTED);

Broadcast Receiver:

// Create the `onReceive()` method in the `CustomBroadcastReceiver` class

Unregistering the receiver:

unregisterReceiver(customBroadcastReceiver);

Types of Broadcast delivery

1. Normal Broadcast

sendBroadcast(intent);

Delivered to all matching receivers
Order is not guaranteed
Fast, simple, chaotic

2. Ordered Broadcast (mostly legacy now)

sendOrderedBroadcast(intent, null);

Delivered one receiver at a time

Receivers can:

Modify the Intent
Abort the broadcast

Used in the past for SMS filtering and similar things.

Modern Android discourages this.

3. Local Broadcast (Deprecated)

LocalBroadcastManager

Only within your app
More efficient
No security risk

Now deprecated because: we can use LiveData, Flow, SharedViewModel, or RxJava

`onReceive()` rules

Inside onReceive():

❌ No long-running tasks

❌ No network calls

❌ No sleep

❌ No heavy database operations

Otherwise, app can get killed or get an ANR.

Allowed:
- Quick checks
- Logging
- Starting a Service
- Scheduling work

Protected Broadcasts

A protected broadcast is a system-level broadcast that third-party apps are NOT allowed to send.
- You can receive it
- You cannot send it
- Android enforces this at runtime
- Violate it and Android throws a SecurityException

Example:

Intent.ACTION_BOOT_COMPLETED

If your app tries:

sendBroadcast(new Intent(Intent.ACTION_BOOT_COMPLETED));

Without protected broadcasts:
- Any app could pretend the phone rebooted
- Fake incoming SMS
- Trigger system alarms
- Mess with power, connectivity, or security flows

Explicit Broadcasts

Intent intent = new Intent(context, MyReceiver.class);
sendBroadcast(intent);

Goes to one specific receiver
No intent filters involved

Implicit Broadcasts

Intent intent = new Intent("com.example.ACTION_SYNC");
sendBroadcast(intent);

Goes to all matching receivers
This is where protected broadcasts matter
Restricted heavily since Android 8.0

Restrict broadcasts with permissions

They are called Permission-Protected Broadcasts.

Here, sending or receiving requires a permission.

Permissions allow you to restrict broadcasts to the set of apps that hold certain permissions.

You can enforce restrictions on either the sender or receiver of a broadcast.

Only receivers who have requested that permission with the <uses-permission> tag in their manifest can receive the broadcast.

Last modified: 05 February 2026