5th February, 2023
Broadcasts is a messaging system between apps in the Android operating system. Android Broadcast is a component in Android that allow the system and other apps to send and receive events.
1. What is Android Broadcast Receiver?
Android Broadcast receiver helps your app to register for events. You will be notified when those events occurred . For example, If you have registered your app for Airplane Mode changes, it will notify when the device gose into Airplane Mode.
In Android,
⇒ Intents are used to broadcast events to other apps.
⇒ To receive broadcast events you need to create a subclass of Android’s BroadcastReceiver class.
⇒ Avoid any long running task in the BroadcastReceiver.
2. Receiving Broadcasts
Below is the sample code of the Android Broadcast Receiver class.
package com.androidchunk.broadcastreceivertest
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.widget.Toast
class MyReceiver : BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent) {
// This method is called
// when the BroadcastReceiver is receiving an Intent broadcast.
Toast.makeText(context, "Intent detected!", Toast.LENGTH_SHORT).show()
}
}
package com.androidchunk.broadcastreceivertest;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.widget.Toast;
class MyReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
// This method is called
// when the BroadcastReceiver is receiving an Intent broadcast.
Toast.makeText(context, "Intent detected!", Toast.LENGTH_SHORT).show();
}
}
You can register a broadcast receiver in two ways.
2.1 Static Broadcast Receivers (Manifest declared receivers)
You can register Android Broadcast receiver by adding <receiver> tag to the androidmanifest.xml file. This method is known as Static Registering Android Broadcast Receivers.
From Android 8.0 or higher, You cannot use this method for most of implicit broadcasts.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<application
...
...
... >
<!--
android:enabled="true" ⇒ this application can be initiated by the system
exported="true" ⇒ this application receives broadcasts from the system
and other apps
-->
<receiver
android:name=".MyReceiver"
android:enabled="true"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.AIRPLANE_MODE" />
</intent-filter>
</receiver>
<activity
android:name=".MainActivity"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
2.1 Dynamic Broadcast Receivers (Context registered receivers)
Another way to register Android Broadcast is by using a context (like activity context, application context, etc). Create a subclass of Android’s BroadcastReceiver class and implement the onReceive() method. Register the Android Broadcast Receiver class by calling registerReceiver() method. This is know as Dynamic Broadcast Receivers or Context Registered Receivers.
package com.androidchunk.broadcastreceivertest
import android.content.Intent
import android.content.IntentFilter
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
//create an object of BroadcastReceiver
private var broadcastReceiver = MyReceiver()
//create an object of IntentFilter
private var intentFilter = IntentFilter(Intent.ACTION_REBOOT)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
override fun onStart() {
super.onStart()
//register broadcast receiver
registerReceiver(broadcastReceiver, intentFilter)
}
override fun onDestroy() {
super.onDestroy()
//unregister broadcast receiver
unregisterReceiver(broadcastReceiver)
}
}
package com.androidchunk.broadcastreceivertest;
import android.content.BroadcastReceiver;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
class MainActivity extends AppCompatActivity {
//create an object of BroadcastReceiver
private BroadcastReceiver broadcastReceiver = new MyReceiver();
//create an object of IntentFilter
private IntentFilter intentFilter = new IntentFilter(Intent.ACTION_REBOOT);
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
protected void onStart() {
super.onStart();
//register broadcast receiver
registerReceiver(broadcastReceiver, intentFilter);
}
@Override
protected void onDestroy() {
super.onDestroy();
//unregister broadcast receiver
unregisterReceiver(broadcastReceiver);
}
}
You can stop receiving broadcasts by calling the unregisterReceiver().
The point to note is that dynamic Broadcast receivers receives broadcasts as long as their context is alive. For example, If you registered your broadcast receiver using an Activity, the receiver receives broadcasts as long as the activity is alive.
Best practices for dynamically registering broadcast receivers in an Activity:
→ If you register broadcast receiver in onCreate(Bundle), Unregister the receiver in onDestroy().
→ If you register broadcast receiver in onResume(), Unregister the receiver in onPause().
3. Sending Broadcasts
In Android, You can send a broadcast in three ways:
| Method | Description |
| sendBroadcast(Intent) | Send broadcasts to all receivers in asynchronous order |
| sendOrderedBroadcast(Intent, String) | Send broadcasts to one receiver at a time |
| LoadBroadcastManager.sendBroadcast | Send broadcast to receivers that are in the same app as the sender |
//create object of Intent class
val intent = Intent()
//Add action
intent.action = "actionXYZ"
//data
intent.putExtra("data", "Hello www.androidchunk.com")
//send broadcast intent
sendBroadcast(intent)
//create object of Intent class
Intent intent = new Intent();
//Add action
intent.setAction("actionXYZ");
//data
intent.putExtra("data","Hello www.androidchunk.com");
//send broadcast intent
sendBroadcast(intent);
4. Android System Broadcast
Android system automatically sends broadcasts when various events have occurred in the device. Some of them are given in the table below.
| Event | Description |
| android.intent.action.BATTERY_LOW | It indicates low battery condition |
| android.intent.action.CONNECTIVITY_CHANGE | It describes that connectivity of the device has changed |
| android.intent.action.POWER_CONNECTED | When power connected to the device |
| android.intent.action.AIRPLANE_MODE | It indicates that the airplane mode changed |
| android.intent.action.CALL_BUTTON | This shows user pressed the call button |
| android.intent.action.DATE_CHANGED | This broadcast trigger when Date of the device changed |
| android.intent.action.VIEW | It displays data to the user |
| android.intent.action.MEDIA_MOUNTED | It indicates media is present and mounted to its mount point |
| android.intent.action.REBOOT | It means the device has rebooted |
5. Implementation of custom Broadcast Receivers in Android
Android allow us to create custom broadcasts. Let’s see how to send and receive custom broadcasts one by one.
Sending custom broadcast
Create an instance of the Intent class and add your string as the intent action. Send it using the sendBroadcast(intent) method.
//create object of Intent class
val intent = Intent()
//Add action
intent.action = "com.androidchunk.broadcastreceivertest.CUSTOM_INTENT"
//data
intent.putExtra("data", "Hello www.androidchunk.com")
//send broadcast intent
sendBroadcast(intent)
//create object of Intent class
Intent intent = new Intent();
//Add action
intent.setAction("com.androidchunk.broadcastreceivertest.CUSTOM_INTENT");
//data
intent.putExtra("data","Hello www.androidchunk.com");
//send broadcast intent
sendBroadcast(intent);
Receiving custom broadcast
To receive a custom broadcast, declare an action in the manifest file. See sample code.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<application
...
...
... >
<receiver
android:name=".MyReceiver">
<intent-filter>
<action android:name="com.androidchunk.broadcastreceivertest.CUSTOM_INTENT" />
</intent-filter>
</receiver>
<activity
android:name=".MainActivity"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
//create object of Intent class
Intent intent = new Intent();
//Add action
intent.setAction("actionXYZ");
//data
intent.putExtra("data","Hello www.androidchunk.com");
//send broadcast intent
sendBroadcast(intent);
Happy coding!