How to make a Drawable(Custom Polygon) part draggable...

Question

I have some Drawable objects in a View. And draw them like this:

protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Drawable1 dr1 = new Drawable1();
    dr1.draw(canvas);
            Drawable2 dr2 = new Drawable2();
    dr2.draw(canvas);
            Drawable3 dr3 = new Drawable3();
    dr3.draw(canvas);
 }

Then how can i make dr1,dr2,dr3 draggable? I can not get focus of them at all.