Send scroll velocity data to Javascript on momentum scroll events.

Reviewed By: sahrens

Differential Revision: D6643379

fbshipit-source-id: 70550274975ed7c2b43a3d668422102d0c115ba7

Author: wwalser

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java

@@ -158,14 +158,16 @@ public boolean onTouchEvent(MotionEvent ev) {
     mVelocityHelper.calculateVelocity(ev);
     int action = ev.getAction() & MotionEvent.ACTION_MASK;
     if (action == MotionEvent.ACTION_UP && mDragging) {
+      float velocityX = mVelocityHelper.getXVelocity();
+      float velocityY = mVelocityHelper.getYVelocity();
       ReactScrollViewHelper.emitScrollEndDragEvent(
         this,
-        mVelocityHelper.getXVelocity(),
-        mVelocityHelper.getYVelocity());
+        velocityX,
+        velocityY);
       mDragging = false;
       // After the touch finishes, we may need to do some scrolling afterwards either as a result
       // of a fling or because we need to page align the content
-      handlePostTouchScrolling();
+      handlePostTouchScrolling(Math.round(velocityX), Math.round(velocityY));
     }
 
     return super.onTouchEvent(ev);
@@ -178,7 +180,7 @@ public void fling(int velocityX) {
     } else {
       super.fling(velocityX);
     }
-    handlePostTouchScrolling();
+    handlePostTouchScrolling(velocityX, 0);
   }
 
   @Override
@@ -270,7 +272,7 @@ public void draw(Canvas canvas) {
    * runnable that checks if we scrolled in the last frame and if so assumes we are still scrolling.
    */
   @TargetApi(16)
-  private void handlePostTouchScrolling() {
+  private void handlePostTouchScrolling(int velocityX, int velocityY) {
     // If we aren't going to do anything (send events or snap to page), we can early out.
     if (!mSendMomentumEvents && !mPagingEnabled && !isScrollPerfLoggingEnabled()) {
       return;
@@ -283,7 +285,7 @@ private void handlePostTouchScrolling() {
     }
 
     if (mSendMomentumEvents) {
-      ReactScrollViewHelper.emitScrollMomentumBeginEvent(this);
+      ReactScrollViewHelper.emitScrollMomentumBeginEvent(this, velocityX, velocityY);
     }
 
     mActivelyScrolling = false;

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java

@@ -279,7 +279,7 @@ public void fling(int velocityY) {
     if (mSendMomentumEvents || isScrollPerfLoggingEnabled()) {
       mFlinging = true;
       enableFpsListener();
-      ReactScrollViewHelper.emitScrollMomentumBeginEvent(this);
+      ReactScrollViewHelper.emitScrollMomentumBeginEvent(this, 0, velocityY);
       Runnable r = new Runnable() {
         @Override
         public void run() {

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java

@@ -44,8 +44,11 @@ public static void emitScrollEndDragEvent(
     emitScrollEvent(scrollView, ScrollEventType.END_DRAG, xVelocity, yVelocity);
   }
 
-  public static void emitScrollMomentumBeginEvent(ViewGroup scrollView) {
-    emitScrollEvent(scrollView, ScrollEventType.MOMENTUM_BEGIN);
+  public static void emitScrollMomentumBeginEvent(
+      ViewGroup scrollView,
+      int xVelocity,
+      int yVelocity) {
+    emitScrollEvent(scrollView, ScrollEventType.MOMENTUM_BEGIN, xVelocity, yVelocity);
   }
 
   public static void emitScrollMomentumEndEvent(ViewGroup scrollView) {