onSharedElementStart
In Activity Transitions, onSharedElementStart is called immediately before capturing the start of the shared element state on enter and reenter transitions and immediately before capturing the end of the shared element state for exit and return transitions.
In Fragment Transitions, onSharedElementStart is called immediately before capturing the start state of all shared element transitions.
This call can be used to adjust the transition start state by modifying the shared element Views. Note that no layout step will be executed between onSharedElementStart and the transition state capture.
For Activity Transitions, any changes made in onSharedElementEnd that are not updated during layout should be corrected in onSharedElementStart for exit and return transitions. For example, rotation or scale will not be affected by layout and if changed in onSharedElementEnd, it will also have to be reset in onSharedElementStart again to correct the end state.
Parameters
The names of the shared elements that were accepted into the View hierarchy.
The shared elements that are part of the View hierarchy.
The Views containing snap shots of the shared element from the launching Window. These elements will not be part of the scene, but will be positioned relative to the Window decor View. This list is null for Fragment Transitions.