Add onChildEndedNativeGesture to JSTouchDispatcher and ReactRootView to handle child gesture finishes event

Summary:
Changelog:
[Android][Added] Adding new API `onChildEndedNativeGesture` to the RootView interface to let its implementations notify the JS side that a child gesture is ended.

Reviewed By: javache

Differential Revision: D32228745

fbshipit-source-id: ad1f26546dd60f9c5a569b0bc3ad5020a01b90cc

Author: ryancat

ReactAndroid/src/main/java/com/facebook/react/ReactRootView.java

@@ -185,14 +185,7 @@ protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 
   @Override
   public void onChildStartedNativeGesture(MotionEvent ev) {
-    if (mReactInstanceManager == null
-        || !mIsAttachedToInstance
-        || mReactInstanceManager.getCurrentReactContext() == null) {
-      FLog.w(TAG, "Unable to dispatch touch to JS as the catalyst instance has not been attached");
-      return;
-    }
-    if (mJSTouchDispatcher == null) {
-      FLog.w(TAG, "Unable to dispatch touch to JS before the dispatcher is available");
+    if (!isDispatcherReady()) {
       return;
     }
     ReactContext reactContext = mReactInstanceManager.getCurrentReactContext();
@@ -209,6 +202,35 @@ public void onChildStartedNativeGesture(View childView, MotionEvent ev) {
     onChildStartedNativeGesture(ev);
   }
 
+  @Override
+  public void onChildEndedNativeGesture(View childView, MotionEvent ev) {
+    if (!isDispatcherReady()) {
+      return;
+    }
+    ReactContext reactContext = mReactInstanceManager.getCurrentReactContext();
+    UIManager uiManager = UIManagerHelper.getUIManager(reactContext, getUIManagerType());
+
+    if (uiManager != null) {
+      EventDispatcher eventDispatcher = uiManager.getEventDispatcher();
+      mJSTouchDispatcher.onChildEndedNativeGesture(ev, eventDispatcher);
+    }
+  }
+
+  private boolean isDispatcherReady() {
+    if (mReactInstanceManager == null
+        || !mIsAttachedToInstance
+        || mReactInstanceManager.getCurrentReactContext() == null) {
+      FLog.w(TAG, "Unable to dispatch touch to JS as the catalyst instance has not been attached");
+      return false;
+    }
+    if (mJSTouchDispatcher == null) {
+      FLog.w(TAG, "Unable to dispatch touch to JS before the dispatcher is available");
+      return false;
+    }
+
+    return true;
+  }
+
   @Override
   public boolean onInterceptTouchEvent(MotionEvent ev) {
     dispatchJSTouchEvent(ev);

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

@@ -50,6 +50,11 @@ public void onChildStartedNativeGesture(
     mTargetTag = -1;
   }
 
+  public void onChildEndedNativeGesture(MotionEvent androidEvent, EventDispatcher eventDispatcher) {
+    // There should be only one child gesture at any given time. We can safely turn off the flag.
+    mChildIsHandlingNativeGesture = false;
+  }
+
   /**
    * Main catalyst view is responsible for collecting and sending touch events to JS. This method
    * reacts for an incoming android native touch events ({@link MotionEvent}) and calls into {@link

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

@@ -22,5 +22,11 @@ public interface RootView {
   /** @deprecated */
   void onChildStartedNativeGesture(MotionEvent ev);
 
+  /**
+   * Called when a child ends a native gesture. Should be called from the child's onTouchIntercepted
+   * implementation.
+   */
+  void onChildEndedNativeGesture(View childView, MotionEvent ev);
+
   void handleException(Throwable t);
 }

ReactAndroid/src/main/java/com/facebook/react/uimanager/events/NativeGestureUtil.java

@@ -25,4 +25,16 @@ public class NativeGestureUtil {
   public static void notifyNativeGestureStarted(View view, MotionEvent event) {
     RootViewUtil.getRootView(view).onChildStartedNativeGesture(view, event);
   }
+
+  /**
+   * Helper method that should be called when a native view ends a native gesture (e.g. a native
+   * ScrollView takes control of a gesture stream and starts scrolling). This will handle
+   * dispatching the appropriate events to JS to make sure future gesture is not blocked.
+   *
+   * @param view the View ending the native gesture
+   * @param event the MotionEvent that caused the gesture to be ended
+   */
+  public static void notifyNativeGestureEnded(View view, MotionEvent event) {
+    RootViewUtil.getRootView(view).onChildEndedNativeGesture(view, event);
+  }
 }

ReactAndroid/src/main/java/com/facebook/react/views/modal/ReactModalHostView.java

@@ -537,6 +537,11 @@ public void onChildStartedNativeGesture(View childView, MotionEvent ev) {
       mJSTouchDispatcher.onChildStartedNativeGesture(ev, mEventDispatcher);
     }
 
+    @Override
+    public void onChildEndedNativeGesture(View childView, MotionEvent ev) {
+      mJSTouchDispatcher.onChildEndedNativeGesture(ev, mEventDispatcher);
+    }
+
     @Override
     public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
       // No-op - override in order to still receive events to onInterceptTouchEvent