title: Android View.onDraw() always has a clean Canvas
body: <p>I am trying to draw an animation.  To do so I have extended View and overridden the onDraw() method.  What I would expect is that each time onDraw() is called the canvas would be in the state that I left it in and I could choose to clear it or just draw over parts of it (This is how it worked when I used a SurfaceView) but each time the canvas comes back already cleared.  Is there a way that I can not have it cleared?  Or maybe save the previous state into a Bitmap so I can just draw that Bitmap and then draw over top of it?</p>