programmatically darken a View android

I would rather do it in the opposite way - put a dark rectangle behind the view and set the view's opacity. This saves painting the rectangle when the view is 100% opaque.

In case of an ImageView, here's one way to achieve it:

imageView.setColorFilter(Color.rgb(123, 123, 123), android.graphics.PorterDuff.Mode.MULTIPLY);