ExampleApplication.java

public class MyApplication extends Application {

  public Registrar registrar;

  protected void onCreate(Bundle savedInstanceState) {
  	super.onCreate(savedInstanceState);
		Registrar r = new Registrar(PUSH_REGISTRATION_URL);
		PushConfig config = new PushConfig(GCM_APP_ID);
		config.setMobileVariantId(AG_PUSH_VARIANT_ID);
		r.register(getApplicationContext(), config, new Callback<Void>() {
		});
	

}

public MyActivity extends Activity implements MessageHandler {
  
  private MyApplication app;
  
  public void onStart() {
    app = ( MyApplication ) getApplication();
  }
  
  public void onResume() {
    app.attachMessageHandlerOnMain(this);
  }
  
  public void onPause() {
    app.detachMessageHandlerOnMain(this);
  }
  
  public void onMessage(Bundle message) {
    Toast.makeToast(message.toString()).show();
  }
  
}

MessageHandler.java

public interface  MessageHandler {

    /**
     * Handle a delete message.  These are sent by Google to notify the applicaiton that messages
     * have been removed on the GCM side and the app needs to do a full update.
     */ 
    public void onDeleteMessage(Bundle message);

  /**
   * This code will be invoked when a message is received (which is not a delete message)
   */ 
    public void onMessage(Bundle message);

    public void onError();
}

Registrar.java

public interface Registrar{
  /**
   * Registers this Installation with Unified push server
   */ 
	public void register(final Context context, final PushConfig config,
			final Callback<Void> callback);
 
  /**
   * Unregisters this Installation with Unified push server.
   * Push notifications will not be received
   */ 
  public void unregister(final Context context, 
			final Callback<Void> callback);
  
  /**
   * Messages received will be handled on the applications Main thread by the handler.
   */ 
   public void attachMessageHandlerOnMain(MessageHandler handler);

  /**
   * Messages received will be handled on a background thread
   */ 
   public void attachMessageHandlerOnBackground(MessageHandler handler);

  /**
   * Messages received will be handled on the applications Main thread by the handler.
   */ 
   public void detachMessageHandlerOnMain(MessageHandler handler);

  /**
   * Messages received will be handled on a background thread
   */ 
   public void detachMessageHandlerOnBackground(MessageHandler handler);


}