Fix touch target for views with z-index

ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactZIndexedViewGroup.java

@@ -0,0 +1,15 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+package com.facebook.react.uimanager;
+
+/**
+ * ViewGroup that supports z-index.
+ */
+public interface ReactZIndexedViewGroup {
+  /**
+   * Determine the index of a child view at {@param index} considering z-index.
+   * @param index The child view index
+   * @return The child view index considering z-index
+   */
+  int getZIndexMappedChildIndex(int index);
+}

ReactAndroid/src/main/java/com/facebook/react/uimanager/TouchTargetHelper.java

@@ -124,8 +124,13 @@ private static View findClosestReactAncestor(View view) {
    */
   private static View findTouchTargetView(float[] eventCoords, ViewGroup viewGroup) {
     int childrenCount = viewGroup.getChildCount();
+    // Consider z-index when determining the touch target.
+    ReactZIndexedViewGroup zIndexedViewGroup = viewGroup instanceof ReactZIndexedViewGroup ?
+      (ReactZIndexedViewGroup) viewGroup :
+      null;
     for (int i = childrenCount - 1; i >= 0; i--) {
-      View child = viewGroup.getChildAt(i);
+      int childIndex = zIndexedViewGroup != null ? zIndexedViewGroup.getZIndexMappedChildIndex(i) : i;
+      View child =  viewGroup.getChildAt(childIndex);
       PointF childPoint = mTempPoint;
       if (isTransformedTouchPointInView(eventCoords[0], eventCoords[1], viewGroup, child, childPoint)) {
         // If it is contained within the child View, the childPoint value will contain the view

ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java

@@ -31,14 +31,16 @@
 import com.facebook.react.uimanager.ReactClippingViewGroup;
 import com.facebook.react.uimanager.ReactClippingViewGroupHelper;
 import com.facebook.react.uimanager.ReactPointerEventsView;
+import com.facebook.react.uimanager.ReactZIndexedViewGroup;
 import com.facebook.react.uimanager.ViewGroupDrawingOrderHelper;
 
 /**
  * Backing for a React View. Has support for borders, but since borders aren't common, lazy
  * initializes most of the storage needed for them.
  */
 public class ReactViewGroup extends ViewGroup implements
-    ReactInterceptingViewGroup, ReactClippingViewGroup, ReactPointerEventsView, ReactHitSlopView {
+    ReactInterceptingViewGroup, ReactClippingViewGroup, ReactPointerEventsView, ReactHitSlopView,
+    ReactZIndexedViewGroup {
 
   private static final int ARRAY_CAPACITY_INCREMENT = 12;
   private static final int DEFAULT_BACKGROUND_COLOR = Color.TRANSPARENT;
@@ -408,6 +410,15 @@ protected int getChildDrawingOrder(int childCount, int index) {
     return mDrawingOrderHelper.getChildDrawingOrder(childCount, index);
   }
 
+  @Override
+  public int getZIndexMappedChildIndex(int index) {
+    if (mDrawingOrderHelper.shouldEnableCustomDrawingOrder()) {
+      return mDrawingOrderHelper.getChildDrawingOrder(getChildCount(), index);
+    } else {
+      return index;
+    }
+  }
+
   @Override
   public PointerEvents getPointerEvents() {
     return mPointerEvents;