Android - Broadcast Receivers

Broadcast Receivers simply respond to broadcast messages from other apppcations or from the system itself. These messages are sometime called events or intents. For example, apppcations can also initiate broadcasts to let other apppcations know that some data has been downloaded to the device and is available for them to use, so this is broadcast receiver who will intercept this communication and will initiate appropriate action.

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

Creating the Broadcast Receiver.

Registering Broadcast Receiver

There is one additional steps in case you are going to implement your custom intents then you will have to create and broadcast those intents.

Creating the 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.

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

Registering Broadcast Receiver

An apppcation pstens 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

<apppcation
   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>
</apppcation>

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

There are several system generated events defined as final static fields in the Intent class. The following table psts a few important system events.

Broadcasting Custom Intents

If you want your apppcation itself should generate and send custom intents then you will have to create and send those intents by using the sendBroadcast() method inside your activity class. If you use the sendStickyBroadcast(Intent) method, the Intent is sticky, meaning the Intent you are sending stays around after the broadcast is complete.

pubpc void broadcastIntent(View view) {
   Intent intent = new Intent();
   intent.setAction("com.tutorialspoint.CUSTOM_INTENT");
   sendBroadcast(intent);
}

This intent com.tutorialspoint.CUSTOM_INTENT can also be registered in similar way as we have regsitered system generated intent.

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

Example

This example will explain you how to create BroadcastReceiver to intercept custom intent. Once you are famipar with custom intent, then you can program your apppcation to intercept system generated intents. So let s follow the following steps to modify the Android apppcation we created in Hello World Example chapter −

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

package com.example.tutorialspoint7.myapppcation;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;

pubpc class MainActivity extends Activity {

   /** Called when the activity is first created. */
   @Override
   
   pubpc void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
   }


   // broadcast a custom intent.
      
   pubpc void broadcastIntent(View view){
      Intent intent = new Intent();
      intent.setAction("com.tutorialspoint.CUSTOM_INTENT"); sendBroadcast(intent);
   }
}

Following is the content of MyReceiver.java:

package com.example.tutorialspoint7.myapppcation;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.widget.Toast;

/**
 * Created by TutorialsPoint7 on 8/23/2016.
 */
pubpc class MyReceiver extends BroadcastReceiver{
   @Override
   pubpc 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.tutorialspoint7.myapppcation">

   <apppcation
      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.tutorialspoint.CUSTOM_INTENT">
            </action>
         </intent-filter>

      </receiver>
   </apppcation>

</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_apgnParentTop="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:onCpck="broadcastIntent"
      android:layout_below="@+id/imageButton"
      android:layout_centerHorizontal="true" />

</RelativeLayout>

Let s try to run our modified Hello World! apppcation we just modified. I assume you had created your AVD while doing environment set-up. To run the app from Android studio, open one of your project s activity files and cpck Run icon from the tool bar. Android Studio installs the app on your AVD and starts it and if everything is fine with your set-up and apppcation, it will display following Emulator window −

Now to broadcast our custom intent, let s cpck on Broadcast Intent button, this will broadcast our custom intent "com.tutorialspoint.CUSTOM_INTENT" which will be intercepted by our registered BroadcastReceiver i.e. MyReceiver and as per our implemented logic a toast will appear on the bottom of the the simulator as follows −

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