叠加图书馆示范
An Overlay Library Demo is to take an existing Android application you may have in your library and invoking a very simple "overlay" View/layer/screen like this application demo.
An Overlay Library Demo is an extra layer that sits on top of a View (the "host view") which is drawn after all other content in that view (including children, if the view is a ViewGroup). Interaction with the overlay layer is done by adding and removing drawables.