Building Android UIs with Custom Views

Adding interactions

Let's start by using the code from the Example25-GLDrawing. Processing user interactions is quite simple, as we have already seen in our previous examples. We don't have to do anything different than before, just override the onTouchEvent() method in our class extending GLSurfaceView and react properly to the different MotionEvents we will receive. For instance, if we don't return true when we receive a MotionEvent.ACTION_DOWN, we will not receive any further events, as we are basically saying that we are not handling the event.

Once we have the source code of the example, let's add a simple implementation of the onTouchEvent() that tracks drag events:

private float dragX; private float dragY; @Override public boolean ...