message: Removed dropped shared element earlier
  The view's already detached in onDropViewInstance so can't get the rootView (and shared element cache). Attached a state listener so notified before the view's detached so can remove it from the shared element cache in the root view
diff: @@ -35,6 +35,19 @@ public class SharedElementManager extends ViewGroupManager<FrameLayout> {
  return true;
  }
  });
  + view.addOnAttachStateChangeListener(new View.OnAttachStateChangeListener() {
  + @Override
  + public void onViewAttachedToWindow(View view) {
  + }
  +
  + @Override
  + public void onViewDetachedFromWindow(View v) {
  + view.removeOnAttachStateChangeListener(this);
  + HashSet<View> sharedElements = getSharedElements(view.getRootView());
  + if (sharedElements != null && sharedElements.contains(view))
  + sharedElements.remove(view);
  + }
  + });
  return view;
  }
  @@ -44,14 +57,6 @@ public class SharedElementManager extends ViewGroupManager<FrameLayout> {
  view.setTransitionName(name);
  }
  - @Override
  - public void onDropViewInstance(FrameLayout view) {
  - HashSet<View> sharedElements = getSharedElements(view.getRootView());
  - if (sharedElements != null && sharedElements.contains(view))
  - sharedElements.remove(view);
  - super.onDropViewInstance(view);
  - }
  -
  @SuppressWarnings("unchecked")
  public static HashSet<View> getSharedElements(View rootView) {
  return (HashSet<View>) rootView.getTag(R.id.sharedElements);
  