I can't give a definitive answer as I've never used it. My best guess comes from working down the inheritance chain...
ViewAnimator...
Base class for a FrameLayout container that will perform animations when switching between its views.
ViewSwitcher
ViewAnimator that switches between two views, and has a factory from which these views are created. You can either use the factory to create the views, or add them yourself. A ViewSwitcher can only have two child views, of which only one is shown at a time.
Then looking at another direct subclass of ViewSwitcher
...
TextSwitcher
Specialized ViewSwitcher that contains only children of type TextView. A TextSwitcher is useful to animate a label on screen. Whenever setText(CharSequence) is called, TextSwitcher animates the current text out and animates the new text in.
So reading between the lines, an ImageSwitcher
is a ViewAnimator
which is optimised for images (i.e., drawables) and as it inherits directly from ViewSwitcher
it can only have two images.
So, paraphrasing the TextSwitcher
overview, I would say that...
Whenever <insert setImageXXX method here>
is called, ImageSwitcher animates the current image out and animates the new image in.
As I said, it's just a 'best guess'.