An extension of LayerDrawables that is intended to cross-fade between the first and second layer. To start the transition, call TransitionDrawable.StartTransition(int). To display just the first layer, call TransitionDrawable.ResetTransition.

It can be defined in an XML file with the <transition> element. Each Drawable in the transition is defined in a nested <item>. For more information, see the guide to Drawable Resources.

[Android Documentation]