This transition tracks changes to the visibility of target views in the
start and end scenes and fades views in or out when they become visible
or non-visible. Visibility is determined by both the
setVisibility(int) state of the view as well as whether it
is parented in the current view hierarchy.
The ability of this transition to fade out a particular view, and the
way that that fading operation takes place, is based on
the situation of the view in the view hierarchy. For example, if a view was
simply removed from its parent, then the view will be added into a ViewGroupOverlay while fading. If a visible view is
changed to be GONE or INVISIBLE, then the
visibility will be changed to VISIBLE for the duration of
the animation. However, if a view is in a hierarchy which is also altering
its visibility, the situation can be more complicated. In general, if a
view that is no longer in the hierarchy in the end scene still has a
parent (so its parent hierarchy was removed, but it was not removed from
its parent), then it will be left alone to avoid side-effects from
improperly removing it from its parent. The only exception to this is if
the previous Scene was
created from a layout resource file, then it is considered safe to un-parent
the starting scene view in order to fade it out.
A Fade transition can be described in a resource file by using the
tag fade, along with the standard
attributes of Fade and Transition.
This method creates an animation that will be run for this transition
given the information in the startValues and endValues structures captured
earlier for the start and end scenes.
Returns the set of property names used stored in the TransitionValues
object passed into captureStartValues(TransitionValues) that
this transition cares about for the purposes of canceling overlapping animations.
This method creates an animation that will be run for this transition
given the information in the startValues and endValues structures captured
earlier for the start and end scenes.