Make Bitmaps listen to touch events

Question

Hi all!

How can I add touch capabilities to a simple bitmap?

I've tried to create a wrapper class for a bitmap,
which implemented OnGestureListener,
but it didn't work.

I want to avoid extending View class to achieve this.

Thanks!

Answer 1

A Bitmap per se is just a representation of an image... thus, in order to show it you will have to draw it somewhere (a View, in fact you always draw it on a View). Then, there's no way to avoid using the View class since all user interface widgets extend it.

In conclusion, if you want to simply set touch listeners to a single Bitmap you can, for instance, draw it on a ImageView and set the appropriate listeners. On the other hand, if you have a set of bitmaps drawn somewhere (for instance, on a SurfaceView), you should locate the bitmap by its coordinates (in that case, the View which would receive the events will be the SurfaceView).

Answer 2

Do you have your OnGestureListener implementation wired to a GestureDetector? The GestureDetector analyzes a MotionEvent and invokes the appropriate callback on the listener based on the type of movement it found.

public class MyActivity extends Activity {
    private GestureDetector detector;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ...
        detector = new GestureDetector(new MyGestureListener());
        ...
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return detector.onTouchEvent(event);
    }
}