Extension function forcing a shared element to run in a ViewGroup overlay.

Transitions.kt

fun Transition.sharedElementsInOverlay(container: ViewGroup, start: View, end: View): Transition =
    addListener(object : Transition.TransitionListener {
      val endParent = end.parent as ViewGroup
      val endOriginalPosition = endParent.indexOfChild(end)

      override fun onTransitionStart(transition: Transition) {
        start.visibility = View.GONE
        container.overlay.add(start)
        container.overlay.add(end)
      }

      override fun onTransitionEnd(transition: Transition) {
        container.overlay.remove(start)
        container.overlay.remove(end)

        if (endParent.isAttachedToWindow) {
          if (endOriginalPosition <= endParent.childCount) {
            endParent.addView(end, endOriginalPosition)
          } else {
            endParent.addView(end)
          }
        }
      }

      override fun onTransitionResume(transition: Transition) {}
      override fun onTransitionPause(transition: Transition) {}
      override fun onTransitionCancel(transition: Transition) {}
    })