onDraw on existing Background

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http://stackoverflow.com – I use my customized camera to capture a image, then I want to draw something on this image. I want to use Canvas, but it doesn't work. Every time when it draws, it also changes the captured image into a white background. Anyone knows how to fix it? bmap is the captured image. Myview is a subclass of View, in which I override onDraw(). Canvas mCanvas = new Canvas(bmap); Myview.SetCanvas(mCanvas); Myview.invalidate(); setContentView(mMask); And If I don't call setContentView, nothing shows up. I have no idea why. Anybody help? (HowTos)