Restful API service

If your service is going to be part of you application then you are making it way more complex than it needs to be. Since you have a simple use case of getting some data from a RESTful Web Service, you should look into ResultReceiver and IntentService.

This Service + ResultReceiver pattern works by starting or binding to the service with startService() when you want to do some action. You can specify the operation to perform and pass in your ResultReceiver (the activity) through the extras in the Intent.

In the service you implement onHandleIntent to do the operation that is specified in the Intent. When the operation is completed you use the passed in ResultReceiver to send a message back to the Activity at which point onReceiveResult will be called.

So for example, you want to pull some data from your Web Service.

1. You create the intent and call startService.
2. The operation in the service starts and it sends the activity a message saying it started
3. The activity processes the message and shows a progress.
4. The service finishes the operation and sends some data back to your activity.
5. Your activity processes the data and puts in in a list view
6. The service sends you a message saying that it is done, and it kills itself.
7. The activity gets the finish message and hides the progress dialog.

I know you mentioned you didn’t want a code base but the open source Google I/O 2010 app uses a service in this way I am describing.

Updated to add sample code:

The activity.

public class HomeActivity extends Activity implements MyResultReceiver.Receiver {

    public MyResultReceiver mReceiver;

    public void onCreate(Bundle savedInstanceState) {
        mReceiver = new MyResultReceiver(new Handler());
        mReceiver.setReceiver(this);
        ...
        final Intent intent = new Intent(Intent.ACTION_SYNC, null, this, QueryService.class);
        intent.putExtra("receiver", mReceiver);
        intent.putExtra("command", "query");
        startService(intent);
    }

    public void onPause() {
        mReceiver.setReceiver(null); // clear receiver so no leaks.
    }

    public void onReceiveResult(int resultCode, Bundle resultData) {
        switch (resultCode) {
        case RUNNING:
            //show progress
            break;
        case FINISHED:
            List results = resultData.getParcelableList("results");
            // do something interesting
            // hide progress
            break;
        case ERROR:
            // handle the error;
            break;
    }
}

The Service:

public class QueryService extends IntentService {
    protected void onHandleIntent(Intent intent) {
        final ResultReceiver receiver = intent.getParcelableExtra("receiver");
        String command = intent.getStringExtra("command");
        Bundle b = new Bundle();
        if(command.equals("query") {
            receiver.send(STATUS_RUNNING, Bundle.EMPTY);
            try {
                // get some data or something           
                b.putParcelableArrayList("results", results);
                receiver.send(STATUS_FINISHED, b)
            } catch(Exception e) {
                b.putString(Intent.EXTRA_TEXT, e.toString());
                receiver.send(STATUS_ERROR, b);
            }    
        }
    }
}

ResultReceiver extension – edited about to implement MyResultReceiver.Receiver

public class MyResultReceiver implements ResultReceiver {
    private Receiver mReceiver;

    public MyResultReceiver(Handler handler) {
        super(handler);
    }

    public void setReceiver(Receiver receiver) {
        mReceiver = receiver;
    }

    public interface Receiver {
        public void onReceiveResult(int resultCode, Bundle resultData);
    }

    @Override
    protected void onReceiveResult(int resultCode, Bundle resultData) {
        if (mReceiver != null) {
            mReceiver.onReceiveResult(resultCode, resultData);
        }
    }
}