title: Android: how to get a faster onDraw()
body: <p>I've created an activity that calls a DrawView extends View, I draw on a Canvas something like a binary tree. The canvas size is greater than the screen size, and the onDraw function draws all the canvas, not only the visible part of it. I've added an horizontal and a vertical scrollView, and obviously onDraw is called again and again to refresh the view. 
  I was wondering if I can draw the canvas on an image (a bitmap or something like that) using that image to show the tree, without the need to recall the onDraw function.
  If I can't do this, what can I do in order to get a faster view?</p>