Binding Services – part 3 (communication Service -> Activity)

In our previous tutorial about IntentService we saw that a BroadcastReceiver can be used as a means of communication between the Service and the calling client. Hower this method cannot be used for frequent and fast calls, such as for progress updates. For this purpose we have to use a different approach...

For more information about binding Services and the way they are connected to a calling Activity, please refer to my previous tutorials.

SERVICE

First of all we have to define a public interface inside our Service as a means of communication between the Service and the calling Activity:

public interface InterfaceCallback {

   void onProgressUpdate(int progress);

   void onTaskCompleted(MyResult myResult);

}

where MyResult is a user defined class carrying the results of the operation performed by the Service in the background.

The next step is to connect our Service to the calling Activity. To do this, we define an instance variable of the type InterfaceCallback and create a public method that will be called by the calling Activity to connect itself to the Service (the following code goes inside the Service class):

private InterfaceCallback interfaceCallback;

...

public void setInterfaceCallback(InterfaceCallback interfaceCallback) {

   this.interfaceCallback = interfaceCallback;

}

Now our Service is ready to communicate with the calling Activity using the interfaceCallback reference. For example, if we want to notify the updates of a background task (from the onProgressUpdate method of an AsyncTask, for instance) we can call:

interfaceCallback.onProgressUpdate(progress);

In the same way, if we need to communicate that the background operation has been completed and send and object containing the results, we can simply call:

interfaceCallback.onTaskCompleted(myResult);

CALLING ACTIVITY

To make sure that our Activity can receive updates from the Service we have to implement the previously defined interface:

public class CallingActivity extends Activity implements ServiceConnection, MyService.InterfaceCallback {

//see previous tutorial

}

Once we have established a valid connection with the Service, we can register our Activity as a callback (our Activity overrides the InterfaceCallback methods that are triggered by the Service):

@Override

public void onServiceConnected(ComponentName componentName, IBinder iBinder) {

  MyService myService = ((MyService.MyBinder) iBinder).getReference();

   myService.setInterfaceCallback(this);

myService.startBackgroundTask();

}

@Override

protected void onPause() {

   super.onPause();

   ...

   if(myService != null) {

      myService.setInterfaceCallback(null);

      unbindService(this);

   }

}

Finally we have to override the methods onProgressUpdate and onTaskCompleted of the implemented InterfaceCallback interface. These methods, as we already saw, are called from the Service to notify the connected Activity about the progress updates and the completion of the background task:

@Override

public void onProgressUpdate(int progress) {

   //code left out for brevity

}

@Override

public void onTaskCompleted(MyResult myResult) {

   //code left out for brevity

}

to be continued...