How to circular reveal the entire activity

Question

I tried using android:windowEnterTransition and android:windowExitTransition but that seems to animate each view in the activity, i.e. revealing each view separately. How can I animate the whole activity with content on it? There are no shared elements between two activities.

Answer 1

After a lot of research and android source code reading, I figured out how to do this. It's in Scala but you should translate that to Java easily.

The following are the most important parts.

CircularRevealActivity.scala:

override protected def onCreate(savedInstanceState: Bundle) {
  super.onCreate(savedInstanceState)
  val window = getWindow
  val decor = window.getDecorView.asInstanceOf[ViewGroup]
  // prevent fading of background
  decor.setBackgroundColor(android.R.color.transparent)
  if (Build.version >= 21) {
    window.setEnterTransition(circularRevealTransition)
    window.setReturnTransition(circularRevealTransition)
    // decor.setTransitionGroup(true) won't work
    for (i <- 0 until decor.getChildCount) {
      val child = decor.getChildAt(i).asInstanceOf[ViewGroup]
      if (child != null) child.setTransitionGroup(true)
    }
    if (savedInstanceState == null) {
      val intent = getIntent
      val x = intent.getFloatExtra(EXTRA_SPAWN_LOCATION_X, Float.NaN)
      if (!x.isNaN) {
        val y = intent.getFloatExtra(EXTRA_SPAWN_LOCATION_Y, Float.NaN)
        if (!y.isNaN) circularRevealTransition.spawnLocation = (x, y)
      }
    }
  }
}

CircularReveal.scala:

@TargetApi(21)
class CircularReveal(context: Context, attrs: AttributeSet = null)
  extends Visibility(context, attrs) {
  var spawnLocation: (Float, Float) = _
  var stopper: View = _
  private val metrics = new DisplayMetrics
  private lazy val wm = context.getSystemService(Context.WINDOW_SERVICE)
    .asInstanceOf[WindowManager]
  private def getEnclosingCircleRadius(x: Float, y: Float) =
    math.hypot(math.max(x, metrics.widthPixels - x),
               math.max(y, metrics.widthPixels - y)).toFloat

  override def onAppear(sceneRoot: ViewGroup, view: View,
                        startValues: TransitionValues, endValues: TransitionValues) = {
    wm.getDefaultDisplay.getMetrics(metrics)
    val (x, y) = LocationObserver.getRelatedTo(spawnLocation, view)
    new NoPauseAnimator(ViewAnimationUtils
      .createCircularReveal(view, x.toInt, y.toInt, 0,
        getEnclosingCircleRadius(x, y)))
  }
  override def onDisappear(sceneRoot: ViewGroup, view: View,
                           startValues: TransitionValues, endValues: TransitionValues) = {
    wm.getDefaultDisplay.getMetrics(metrics)
    val (x, y) = if (stopper == null)
      LocationObserver.getRelatedTo((metrics.widthPixels * .5F,
        metrics.heightPixels.toFloat), view)
    else LocationObserver.getRelatedTo(stopper, view)
    new NoPauseAnimator(ViewAnimationUtils
      .createCircularReveal(view, x.toInt, y.toInt,
        getEnclosingCircleRadius(x, y), 0))
  }
}