Sending broadcasts within your app with a local BroadcastReceiver

In this tutorial I will explain how to send broadcasts within your own app using the LocalBroadcastManager.

To begin with, let’s start with a FAQ.

What is a BroadcastReceiver?

An Android app is made of components, including Application, Activity, Service, ContentProvider and BroacastReceiver, each of which used for a particular purpose.

So a BroadcastReceiver is a component (optional) of an Android app.

What are BroadcastReceivers generally used for?

BroadcastReceiver is a component running in the background and listening to “broacasts” sent by the Android system or by an Android app.

For example, when the user turns on or off the screen, when the level of the battery changes, when wifi is connected/disconnected, etc., the Android system sends a “broacast” with the relevant information about the event that has occured. You can set up a BroadcastReceiver that intercepts this event and performs a certain action in response (for example, starting a Service).

In your own app you can also send broacasts containing information and set up a BroacastReceiver that listens to these broadcasts and performs certain actions in response. We already saw an example in a previous tutorial about the IntentService class, with which you can use a Service to perform slow or long running operations in a background thread.

When the IntentService finishes its task you may want to communicate the result back to the calling Activity: to do this you have to send a broadcast within your IntentService containing the relevant information, and set up a BroadcastReceiver within you Activity to listen to the result.

So, what is a local BroadcastReceiver?

BroadcastReceiver is generally used to send/receive broacasts between different processes (for example, different apps) because it implements an inter process communication system.

But if the “broadcaster” and the BroadcastReceiver belong to the same process (for example, sending broacasts within your own app), a local BroadcastReceiver, which is managed by the LocalBroadcastManager class, is much more efficient.

In addition to that a local BroadcastReceiver is more secure because all relevant information stays within your own app and is not visible outside.

So a local BroadcastReceiver is a more efficient and secure BroacastReceiver that works only within your own app.

Now let’s see how to implement a local BroadcastReceiver within your Activity (here you can download the code in a more readable format):

public class YourClass extends Activity {

//the main code of the Activity is omitted for brevity

// used for filtering broadcasts (the receiver listens only to Intents with “myBroacast” set as action in the constructor)

public static final String MY_ACTION = “myBroacast”;

@Override

protected void onResume() {

super.onResume(); //call the superclass first

LocalBroadcastManager myLocalBroadcastManager = LocalBroadcastManager.getInstance(this);

IntentFilter myIntentFilter = new IntentFilter(MY_ACTION);

//set up the local LocalBroadcastReceiver

myLocalBroadcastReceiver = new BroadcastReceiver() {

@Override

public void onReceive(Context context, Intent intent) {

//handle the broadcast here

}

};

//register the local BroadcastReceiver with the specified intent filter

myLocalBroadcastManager.registerReceiver(myLocalBroadcastReceiver, myIntentFilter);

}

@Override

protected void onPause() {

super.onPause();

LocalBroadcastManager myLocalBroadcastManager = LocalBroadcastManager.getInstance(this);

//always unregister the receiver when it’s no longer needed to save resources

myLocalBroadcastManager.unregisterReceiver(myLocalBroadcastReceiver);

}

//instance variables

private BroadcastReceiver myLocalBroadcastReceiver;

}

When you want to send a local broadcast, you just have to use the following code:

//create an Intent with the action “myBroadcast” (the filter used in our local receiver)

Intent localBroadcastIntent = new Intent(“myBroacast”);

//you can add additional info to the Intent

localBroadcastIntent.putExtra(“risult”, risult);

LocalBroadcastManager myLocalBroadcastManager = LocalBroadcastManager.getInstance(this);

myLocalBroadcastManager.sendBroacast(localBroadcastIntent);

Using directed broadcasts

Another way of sending broacasts within you own app is by using directed broadcasts, explicitly specifying the BroadcastReceiver that has to intercept them.

You just have to set the ComponentName in the Intent:

Intent myIntent = new Intent(action);

myIntent.setComponent(new ComponentName(packageName, className));

sendBroadcast(myIntent);

action = String representing the filter used by our BroadcastReceiver

packageName = String representing the name of the package of our BroadcastReceiver (like “com.androidthetechnicalblog.example”)

className = String representing the name of the class of our BroadcastReceiver

This way our broadcast is received only by the specified BroadcastReceiver.

Directed broadcasts can also be used with different processes/applications.

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