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Alex Rivera
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I have a custom view that fills my entire screen. (A piano keyboard) When a user touches the key, it causes invalidate() to be called and the whole keyboard gets redrawn to show the new state with a touched key. Currently the view is very simple, but I plan to add a bit more nice graphics. Since the whole keyboard is dynamically rendered this would make redrawing the entire keyboard more expensive. So I thought, let's look into partial redrawing. Now I call invalidate(Rect dirty) with the correct dirty region. I set my onDraw(Canvas canvas) method to only draw the keys in the dirty region if I do indeed want a partial redraw. This results in those keys being drawn, but the rest of the keyboard is totally black/not drawn at all. Am I wrong in expecting that calling invalidate(Rect dirty) would "cache" the current canvas , and only "allows" drawing in the dirty region? Is there any way I can achieve what I want? (A way to "cache" the canvas and only redraw the dirty area?"
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