How Many Services Can A Broadcast Listener Register For On Android

Local Broadcast, less overhead and secure in Android

Circulate receiver is an Android component which allows y'all to send or receive Android system or application events. All the registered application are notified by the Android runtime in one case result happens.

It works similar to the publish-subscribe design blueprint and used for asynchronous inter-process communication.

For example, applications tin register for various system events like kicking consummate or battery depression, and Android system sends broadcast when specific issue occur. Any application can too create its own custom broadcasts.

Basics of Broadcast

Let's talk over some basic concepts of broadcast receiver.

Register Broadcast

There are ii means to annals broadcast receiver-

Manifest-declared (Statically) : By this receiver can be registered via the AndroidManifest.xml file.

Context-registered (Dynamically) : By this annals a receiver dynamically via the Context.registerReceiver() method.

Receive Broadcasts

To be able to receive a broadcast, application take to extends the BroadcastReceiver abstract form and override its onReceive() method.

If the event for which the broadcast receiver has registered happens, the onReceive() method of the receiver is chosen by the Android system.

Trouble with global broadcast

It is adept practice to utilise broadcast receivers when you desire to transport or receive information between different applications. Just if the communication is limited to your application then it is non good to use the global broadcast.

In this case Android provides local broadcasts with the LocalBroadcastManager class. Using global circulate, any other application can also send and receives circulate messages to and from our application. This can be a serious security thread for our application. Also global broadcast is sent system-wide, so it is not performance efficient.

What is LocalBroadcastManager?

For obvious reasons, global broadcasts must never contain sensitive data. You can, however, broadcast such information locally using the LocalBroadcastManager class, which is a part of the Android Support Library.

The LocalBroadcastManager is much more than efficient as information technology doesn't need inter-process communication.

Below are some of its benefits:

Broadcast data won't leave your app, so don't need to worry about leaking private data.
It is not possible for other applications to send these broadcasts to your app, so you don't demand to worry about having security holes they can exploit.
It is more efficient than sending a global broadcast through the arrangement.
No overhead of system-broad circulate.

Implementation

In that location is no boosted support library dependency required in the latest version of Android Studio. However, if you lot desire to implement local broadcasts in an old projection, following dependency needs to be add in the app module's build.gradle file:

          compile 'com.android.support:support-v4:23.4.0'

Create a new instance of the LocalBroadcastManager

          LocalBroadcastManager localBroadcastManager = LocalBroadcastManager.getInstance(context);

You can at present send local broadcasts using the sendBroadcast() method like

          // Create intent with action          Intent localIntent = new Intent("CUSTOM_ACTION");          // Send local circulate          localBroadcastManager.sendBroadcast(localIntent);

Now create a broadcast receiver that tin can reply to the local-broadcast activity:

          private BroadcastReceiver listener = new BroadcastReceiver() {          @Override                      public void onReceive( Context context, Intent intent ) {                      String data = intent.getStringExtra("DATA");                      Log.d( "Received data : ", information);                      }          };

Dynamically registered receivers must be unregistered when they are no longer necessary like:

          localBroadcastManager.unregisterReceiver(myBroadcastReceiver);

You tin can find the reference code to implement Local Broadcast receiver from GitHub. In the sample code I accept created an IntentService, which broadcasts electric current engagement and it is received by an Activity of the same application.

How to secure broadcasts

Restrict your app to receive broadcast

Specify a permission parameter when registering a broadcast receiver then only broadcasters who have requested the permission can ship an Intent to the receiver.

For example, receiving app has a declared SEND_SMS permission in the receiver as shown below:

          <receiver android:proper name=".MyBroadcastReceiver"                      android:permission="android.permission.SEND_SMS">                      <intent-filter>                      <action android:proper name="android.intent.action.AIRPLANE_MODE"/>                      </intent-filter>          </receiver>

Set the android:exported attribute to "fake" in the manifest. This restrict to receive broadcasts from sources outside of the app.
Limit yourself to only local broadcasts with LocalBroadcastManager.

Control receiver of your broadcast

Y'all tin specify a permission when sending a broadcast and so only receivers who accept requested that permission tin receive the broadcast. For instance, the following code sends a circulate:

          sendBroadcast(new Intent("com.example.NOTIFY"), Manifest.permission.SEND_SMS);

In Android four.0 and higher, you can specify a bundle with setPackage(String) when sending a broadcast. The system restricts the broadcast to the set of apps that match the package.
Send local broadcasts with LocalBroadcastManager.

Conclusion

Hope you understand well-nigh the global and local broadcasts and their security consideration. To better the performance of system Android O has changed the registration of broadcast receiver. From Android O you cannot register implicit broadcasts in your application manifest (few exceptions is there) but application tin can go along to register for explicit broadcasts in their manifests or at run-time. Read more than on broadcast receiver at Android official certificate.

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