In this tutorial we’ll discuss and implement a very important component of the Android Framework named BroadcastReceiver.
Android BroadcastReceiver Overview
A BroadcastReceiver is a dormant component of Android that listens to system-wide broadcast events or intents. When any of these events occur it brings the application into action by either creating a status bar notification or performing a task. Unlike activities, a BroadcastReceiver doesn’t contain any user interface. It’s generally implemented to delegate the tasks to services depending on the type of intent data that’s received. Following are some of the important system wide generated intents.
- android.intent.action.BATTERY_LOW : Indicates low battery condition on the device.
- android.intent.action.BOOT_COMPLETED : This is broadcast once, after the system has finished booting
- android.intent.action.CALL : To perform a call to someone specified by the data
- android.intent.action.DATE_CHANGED : The date has changed
- android.intent.action.REBOOT : Have the device reboot
- android.net.conn.CONNECTIVITY_CHANGE : The mobile network or wifi connection is changed(or reset)
To set up a Broadcast Receiver in our android application we need to do the following two things.
- Creating a BroadcastReceiver
- Registering a BroadcastReceiver
Creating a BroadcastReceiver
Let’s quickly implement a custom BroadcastReceiver as shown below:
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public class MyReceiver extends BroadcastReceiver { public MyReceiver() { } @Override public void onReceive(Context context, Intent intent) { Toast.makeText(context, "Action: " + intent.getAction(), Toast.LENGTH_SHORT).show(); } } |
BroadcastReceiver is an abstract class with the onReceiver() method being abstract. The onReceiver()method is first called on the registered BroadcastReceivers when any event occurs. The intent object is passed with all the additional data. A Context object is also available and is used to start an activity or service using context.startActivity(myIntent); or context.startService(myService); respectively.
Registering the BroadcastReceiver
A BroadcastReceiver can be registered in two ways:
By defining it in the AndroidManifest.xml file as shown below.
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<receiver android:name=".ConnectionReceiver" > <intent-filter> <action android:name="android.net.conn.CONNECTIVITY_CHANGE" /> </intent-filter> </receiver> |
Using intent filters we tell the system any intent that matches our subelements should get delivered to that specific broadcast receiver.
- By defining it programmatically
Following snippet shows a sample example.
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IntentFilter filter = new IntentFilter(); intentFilter.addAction(getPackageName() + "android.net.conn.CONNECTIVITY_CHANGE"); MyReceiver myReceiver = new MyReceiver(); registerReceiver(myReceiver, filter); |
To unregister a receiver in onStop() or onPause() of the activity the following snippet can be used.
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@Override protected void onPause() { unregisterReceiver(myReceiver); super.onPause(); } |
Sending Broadcast intents from the Activity
The following snippet is used to send an intent to all the related BroadcastReceivers.
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Intent intent = new Intent(); intent.setAction("com.journaldev.CUSTOM_INTENT"); sendBroadcast(intent); |
Don’t forget to add the above action in the intent filter tag of the manifest or programmatically.
Let’s develop an application that listens to network change events and also to a custom intent and handles the data accordingly.
Project Structure
Code
The activity_main.xml consists of a button at the center that sends a broadcast intent.
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<?xml version="1.0" encoding="utf-8"?> <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:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.journaldev.broadcastreceiver.MainActivity"> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/button" android:text="Send Broadcast" android:layout_centerVertical="true" android:layout_centerHorizontal="true" /> </RelativeLayout> |
The
MainActivity.java is given below.
MainActivity.java
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package com.journaldev.broadcastreceiver; import android.content.Intent; import android.content.IntentFilter; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import butterknife.ButterKnife; import butterknife.InjectView; import butterknife.OnClick; public class MainActivity extends AppCompatActivity { ConnectionReceiver receiver; IntentFilter intentFilter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ButterKnife.inject(this); receiver = new ConnectionReceiver(); intentFilter = new IntentFilter("com.journaldev.broadcastreceiver.SOME_ACTION"); } @Override protected void onResume() { super.onResume(); registerReceiver(receiver, intentFilter); } @Override protected void onDestroy() { super.onDestroy(); unregisterReceiver(receiver); } @OnClick(R.id.button) void someMethod() { Intent intent = new Intent("com.journaldev.broadcastreceiver.SOME_ACTION"); sendBroadcast(intent); } } |
In the above code we’ve registered another custom action programmatically.
The ConnectionReceiver is defined in the AndroidManifest.xml file as below:
AndroidManifest.xml
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<?xml version="1.0" encoding="utf-8"?> <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.journaldev.broadcastreceiver"> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <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=".ConnectionReceiver"> <intent-filter> <action android:name="android.net.conn.CONNECTIVITY_CHANGE" /> </intent-filter> </receiver> </application> </manifest> |
The ConnectionReceiver.java class is defined below.
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public class ConnectionReceiver extends BroadcastReceiver { @Override public void onReceive(Context context, Intent intent) { Log.d("API123",""+intent.getAction()); if(intent.getAction().equals("com.journaldev.broadcastreceiver.SOME_ACTION")) Toast.makeText(context, "SOME_ACTION is received", Toast.LENGTH_LONG).show(); else { ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE); NetworkInfo activeNetwork = cm.getActiveNetworkInfo(); boolean isConnected = activeNetwork != null && activeNetwork.isConnectedOrConnecting(); if (isConnected) { try { Toast.makeText(context, "Network is connected", Toast.LENGTH_LONG).show(); } catch (Exception e) { e.printStackTrace(); } } else { Toast.makeText(context, "Network is changed or reconnected", Toast.LENGTH_LONG).show(); } } } } |
In the above code we check the intent action that triggers the onReceive() method and based on that display the toast.
Note: To make the receiver unavailable to external applications, add the attribute android:exported=falsein the manifest. When we send a broadcast, it is possible for the external applications too to receive them. This can be prevented by specifying this limitation.
The output app in action is given below.
This brings an end to this tutorial. You can download the final BroadcastReceivers project from the link below.