使用Android的内置手势监听器和缩放监听器实现捏缩放和拖动

I am trying to implement pinch zoom and drag using Android's gesture listener and scale listener. The problem is that when I perform pinch zoom, the image (which I am trying to zoom) bounces to a particular location. Also the zoom position is not centered. The following code demonstrates what I am trying to achieve. Any idea why the image is jumping (and how to correct it) ?I am trying to implement pinch zoom and drag us