Detecting when a View has been invalidated

In a custom View, I need to perform some additional work inside onDraw() if and only if the View was invalidated by the application; that is, my own code called invalidate() in the UI thread or postInvalidate() in a non-UI thread. If on the other hand onDraw() is being called because the system invalidated the View, I don't wish that additional work to be performed.

What's the best way to achieve this? My immediate thought is to simply override invalidate() and postInvalidate() and set a flag in both of tho开发者_C百科se, but it would be nicer if there was a single UI-thread method I could override.

Any thoughts please?

Thanks, Trev

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postInvalidate() ends up calling invalidate() so you don't need to override both. But if you override invalidate(), the system will call the overridden version.

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There is a way to do that without extending view class.

view.getViewTreeObserver().addOnDrawListener(new ViewTreeObserver.OnDrawListener() {
        @Override
        public void onDraw() {
            //View was invalidated
        }
    });