disable momentum scrolling for horizontal ScrollView (#24045)

Summary:
Would like feedback from the community as this may not be the best solution for all

I would like to restrict (or paginate) the fling of a horizontal ScrollView when `snapToInterval` is set. This is not currently possible with `pagingEnabled`, since the pagination works only when items are the entire width of the ScrollView.

This implementation simply restricts the predicted `targetOffset` found from the `x` velocity and replaces it with the offset when the pan gesture ended.

To get pagination working, I may paginate based on the interval by calculating the offset delta from the beginning of the gesture to current offset and restricting the scrolling behavior to the `snapToInterval`. If this is preferred, I can update this PR or make a new one, but wanted to start a discussion since it seems like there are many in the community that would like this feature  #21302 .

[General] [Added] - add prop `disableIntervalMomentum` to disable the predictive scrolling behavior of horizontal ScrollViews
Pull Request resolved: #24045

Differential Revision: D14939754

Pulled By: sahrens

fbshipit-source-id: 26be19c47dfb8eed4d7e6035df53a77451e23081

Libraries/Components/ScrollView/ScrollView.js

@@ -368,6 +368,13 @@ export type Props = $ReadOnly<{|
    * ```
    */
   contentContainerStyle?: ?ViewStyleProp,
+  /**
+   * When true, the scroll view stops on the next index (in relation to scroll
+   * position at release) regardless of how fast the gesture is. This can be
+   * used for horizontal pagination when the page is less than the width of
+   * the ScrollView. The default value is false.
+   */
+  disableIntervalMomentum?: ?boolean,
   /**
    * A floating-point number that determines how quickly the scroll view
    * decelerates after the user lifts their finger. You may also use string

React/Views/ScrollView/RCTScrollView.h

@@ -46,6 +46,7 @@
 @property (nonatomic, copy) NSDictionary *maintainVisibleContentPosition;
 @property (nonatomic, assign) BOOL scrollToOverflowEnabled;
 @property (nonatomic, assign) int snapToInterval;
+@property (nonatomic, assign) BOOL disableIntervalMomentum;
 @property (nonatomic, copy) NSArray<NSNumber *> *snapToOffsets;
 @property (nonatomic, assign) BOOL snapToStart;
 @property (nonatomic, assign) BOOL snapToEnd;

React/Views/ScrollView/RCTScrollView.m

@@ -855,7 +855,11 @@ - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoi
 
     // What is the current offset?
     CGFloat velocityAlongAxis = isHorizontal ? velocity.x : velocity.y;
-    CGFloat targetContentOffsetAlongAxis = isHorizontal ? targetContentOffset->x : targetContentOffset->y;
+    CGFloat targetContentOffsetAlongAxis = targetContentOffset->y;
+    if (isHorizontal) {
+      // Use current scroll offset to determine the next index to snap to when momentum disabled
+      targetContentOffsetAlongAxis = self.disableIntervalMomentum ? scrollView.contentOffset.x : targetContentOffset->x;
+    }
 
     // Offset based on desired alignment
     CGFloat frameLength = isHorizontal ? self.frame.size.width : self.frame.size.height;
@@ -868,6 +872,7 @@ - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoi
 
     // Pick snap point based on direction and proximity
     CGFloat fractionalIndex = (targetContentOffsetAlongAxis + alignmentOffset) / snapToIntervalF;
+
     NSInteger snapIndex =
       velocityAlongAxis > 0.0 ?
         ceil(fractionalIndex) :

React/Views/ScrollView/RCTScrollViewManager.m

@@ -85,6 +85,7 @@ - (UIView *)view
 RCT_EXPORT_VIEW_PROPERTY(scrollIndicatorInsets, UIEdgeInsets)
 RCT_EXPORT_VIEW_PROPERTY(scrollToOverflowEnabled, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(snapToInterval, int)
+RCT_EXPORT_VIEW_PROPERTY(disableIntervalMomentum, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(snapToOffsets, NSArray<NSNumber *>)
 RCT_EXPORT_VIEW_PROPERTY(snapToStart, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(snapToEnd, BOOL)

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

@@ -65,6 +65,7 @@ public class ReactHorizontalScrollView extends HorizontalScrollView implements
   private @Nullable String mScrollPerfTag;
   private @Nullable Drawable mEndBackground;
   private int mEndFillColor = Color.TRANSPARENT;
+  private boolean mDisableIntervalMomentum = false;
   private int mSnapInterval = 0;
   private float mDecelerationRate = 0.985f;
   private @Nullable List<Integer> mSnapOffsets;
@@ -141,6 +142,10 @@ public boolean getRemoveClippedSubviews() {
     return mRemoveClippedSubviews;
   }
 
+  public void setDisableIntervalMomentum(boolean disableIntervalMomentum) {
+    mDisableIntervalMomentum = disableIntervalMomentum;
+  }
+
   public void setSendMomentumEvents(boolean sendMomentumEvents) {
     mSendMomentumEvents = sendMomentumEvents;
   }
@@ -579,6 +584,10 @@ private void flingAndSnap(int velocityX) {
 
     int maximumOffset = Math.max(0, computeHorizontalScrollRange() - getWidth());
     int targetOffset = predictFinalScrollPosition(velocityX);
+    if (mDisableIntervalMomentum) {
+      targetOffset = getScrollX();
+    }
+
     int smallerOffset = 0;
     int largerOffset = maximumOffset;
     int firstOffset = 0;

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

@@ -80,6 +80,11 @@ public void setDecelerationRate(ReactHorizontalScrollView view, float decelerati
     view.setDecelerationRate(decelerationRate);
   }
 
+  @ReactProp(name = "disableIntervalMomentum")
+  public void setDisableIntervalMomentum(ReactHorizontalScrollView view, boolean disbaleIntervalMomentum) {
+    view.setDisableIntervalMomentum(disbaleIntervalMomentum);
+  }
+
   @ReactProp(name = "snapToInterval")
   public void setSnapToInterval(ReactHorizontalScrollView view, float snapToInterval) {
     // snapToInterval needs to be exposed as a float because of the Javascript interface.