Why is requestLayout being called directly after invalidate

Question

I\'m learning about custom views and wanted to learn about invalidate() and requestLayout().

Please refer to this answer and its diagram:

Answer 1

After seeing the following diagram, I was under the impression that calling requestLayout() would eventually result in an onDraw.

Therefore, there would be no need to call these together because it would be redundant.

invalidate();
requestLayout();

However, it turns out that that diagram is misleading. Some views might in fact invalidate themselves when there is a layout change, but this is not a certainty. Calling requestLayout() is not guaranteed to result in onDraw being called.

My source (thanks to this comment) is the Romain Guy (who is an Android engineer at Google):

requestLayout() itself does not lead to a draw pass but some views might react to a Layout change by calling invalidate.

Therefore, to be certain a relayout will result in a redraw, then you should pair an invalidate() with the requestLayout(). (The opposite is not true, though. If you only need a redraw, then there is no need to call requestLayout(). A single invalidate() will do.)