View.onDraw（） - 什么时候被调用？

I put a Log.d() call into the onDraw() of my extended View, so I could see how often and when it's getting called. It gets called upon instantiation of the view, which is not surprising. But then I notice, it gets called on every tap that is handled by onTouchEvent(), even though my code there isn't doing anything remotely related to graphics. However, in the I put a Log.d() call into the onDraw() of my ex