Android - Broadcast Receivers

Broadcast Receivers simply respond to broadcast messages from other applications or from the system itself. These messages are also called as events or intents.

There are following two important steps to make BroadcastReceiver works for the system broadcasted intents −

·        Creating the Broadcast Receiver.

·        Registering Broadcast Receiver

A broadcast receiver is implemented as a subclass of BroadcastReceiver class and overriding the onReceive() method where each message is received as a Intent object parameter.

Registering Broadcast Receiver

An application listens for specific broadcast intents by registering a broadcast receiver in AndroidManifest.xml file. Consider we are going to register MyReceiver for system generated event ACTION_BOOT_COMPLETED which is fired by the system once the Android system has completed the boot process.

BROADCAST-RECEIVER

<application   android:icon="@drawable/ic_launcher"   android:label="@string/app_name"   android:theme="@style/AppTheme" >   <receiver android:name="MyReceiver"> 
      <intent-filter>         <action android:name="android.intent.action.BOOT_COMPLETED">         </action>      </intent-filter> 
   </receiver></application>

Now whenever your Android device gets booted, it will be intercepted by BroadcastReceiver MyReceiver and implemented logic inside onReceive() will be executed.

Following is the content of the modified main activity file MainActivity.java. This file can include each of the fundamental life cycle methods. We have added broadcastIntent() method to broadcast a custom intent.

package com.example.myapplication; import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.view.View; public class MainActivity extends Activity { 
   @Override 
   public void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.activity_main);   } 
    
   public void broadcastIntent(View view){      Intent intent = new Intent();      intent.setAction("com.example.CUSTOM_INTENT"); sendBroadcast(intent);   }}

Following is the content of MyReceiver.java:

package com.example.myapplication; import android.content.BroadcastReceiver;import android.content.Context;import android.content.Intent;import android.widget.Toast; 

public class MyReceiver extends BroadcastReceiver{   @Override   public void onReceive(Context context, Intent intent) {      Toast.makeText(context, "Intent Detected.", Toast.LENGTH_LONG).show();   }}

Following will the modified content of AndroidManifest.xml file. Here we have added <receiver.../> tag to include our service:

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"   package="com.example.myapplication">    <application      android:allowBackup="true"      android:icon="@mipmap/ic_launcher"      android:label="@string/app_name"      android:supportsRtl="true"      android:theme="@style/AppTheme">             
      <activity android:name=".MainActivity">         <intent-filter>            <action android:name="android.intent.action.MAIN" />             <category android:name="android.intent.category.LAUNCHER" />         </intent-filter>      </activity> 
      <receiver android:name="MyReceiver">         <intent-filter>            <action android:name="com.example.CUSTOM_INTENT">            </action>         </intent-filter>       </receiver>   </application> </manifest>

Following will be the content of res/layout/activity_main.xml file to include a button to broadcast our custom intent −

<RelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"   xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"   android:layout_height="match_parent"    android:paddingLeft="@dimen/activity_horizontal_margin"   android:paddingRight="@dimen/activity_horizontal_margin"   android:paddingTop="@dimen/activity_vertical_margin"   android:paddingBottom="@dimen/activity_vertical_margin"    tools:context=".MainActivity"> 
   <TextView      android:id="@+id/textView1"      android:layout_width="wrap_content"      android:layout_height="wrap_content"      android:text="Example of Broadcast"      android:layout_alignParentTop="true"      android:layout_centerHorizontal="true"      android:textSize="30dp" />    
   <TextView      android:id="@+id/textView2"      android:layout_width="wrap_content"      android:layout_height="wrap_content"      android:text="Tutorials point "      android:textColor="#ff87ff09"      android:textSize="30dp"      android:layout_above="@+id/imageButton"      android:layout_centerHorizontal="true"      android:layout_marginBottom="40dp" />    
   <ImageButton      android:layout_width="wrap_content"      android:layout_height="wrap_content"      android:id="@+id/imageButton"      android:src="@drawable/abc"      android:layout_centerVertical="true"      android:layout_centerHorizontal="true" />    
   <Button      android:layout_width="wrap_content"      android:layout_height="wrap_content"      android:id="@+id/button2"      android:text="Broadcast Intent"      android:onClick="broadcastIntent"      android:layout_below="@+id/imageButton"      android:layout_centerHorizontal="true" /> </RelativeLayout>

You can try implementing other BroadcastReceiver to intercept system generated intents like system boot up, date changed, low battery etc.