Implement onMomentumScrollEnd and onMomentumScrollBegin for Fabric ScrollView

Co-authored-by: anupriya13 <[email protected]>

Author: Copilot

vnext/Microsoft.ReactNative/CompositionSwitcher.idl

@@ -118,6 +118,8 @@ namespace Microsoft.ReactNative.Composition.Experimental
     event Windows.Foundation.EventHandler<IScrollPositionChangedArgs> ScrollPositionChanged;
     event Windows.Foundation.EventHandler<IScrollPositionChangedArgs> ScrollBeginDrag;
 	  event Windows.Foundation.EventHandler<IScrollPositionChangedArgs> ScrollEndDrag;
+    event Windows.Foundation.EventHandler<IScrollPositionChangedArgs> ScrollMomentumBegin;
+    event Windows.Foundation.EventHandler<IScrollPositionChangedArgs> ScrollMomentumEnd;
     void ContentSize(Windows.Foundation.Numerics.Vector2 size);
     Windows.Foundation.Numerics.Vector3 ScrollPosition { get; };
     void ScrollBy(Windows.Foundation.Numerics.Vector3 offset, Boolean animate);

vnext/Microsoft.ReactNative/Fabric/Composition/CompositionContextHelper.cpp

@@ -711,6 +711,10 @@ struct CompScrollerVisual : winrt::implements<
     void IdleStateEntered(
         typename TTypeRedirects::InteractionTracker sender,
         typename TTypeRedirects::InteractionTrackerIdleStateEnteredArgs args) noexcept {
+      if (m_outer->m_inertia) {
+        // We were in inertia and now we're idle, so momentum scrolling has ended
+        m_outer->FireScrollMomentumEnd({sender.Position().x, sender.Position().y});
+      }
       m_outer->m_custom = false;
       m_outer->m_inertia = false;
     }
@@ -725,6 +729,8 @@ struct CompScrollerVisual : winrt::implements<
       // 2. tracker has just started gliding into Inertia state
       // Fire ScrollEndDrag
       m_outer->FireScrollEndDrag({args.NaturalRestingPosition().x, args.NaturalRestingPosition().y});
+      // Fire momentum scroll begin when we enter inertia
+      m_outer->FireScrollMomentumBegin({args.NaturalRestingPosition().x, args.NaturalRestingPosition().y});
     }
     void InteractingStateEntered(
         typename TTypeRedirects::InteractionTracker sender,
@@ -985,6 +991,20 @@ struct CompScrollerVisual : winrt::implements<
     return m_scrollEndDragEvent.add(handler);
   }
 
+  winrt::event_token ScrollMomentumBegin(
+      winrt::Windows::Foundation::EventHandler<
+          winrt::Microsoft::ReactNative::Composition::Experimental::IScrollPositionChangedArgs> const
+          &handler) noexcept {
+    return m_scrollMomentumBeginEvent.add(handler);
+  }
+
+  winrt::event_token ScrollMomentumEnd(
+      winrt::Windows::Foundation::EventHandler<
+          winrt::Microsoft::ReactNative::Composition::Experimental::IScrollPositionChangedArgs> const
+          &handler) noexcept {
+    return m_scrollMomentumEndEvent.add(handler);
+  }
+
   void ScrollPositionChanged(winrt::event_token const &token) noexcept {
     m_scrollPositionChangedEvent.remove(token);
   }
@@ -997,6 +1017,14 @@ struct CompScrollerVisual : winrt::implements<
     m_scrollEndDragEvent.remove(token);
   }
 
+  void ScrollMomentumBegin(winrt::event_token const &token) noexcept {
+    m_scrollMomentumBeginEvent.remove(token);
+  }
+
+  void ScrollMomentumEnd(winrt::event_token const &token) noexcept {
+    m_scrollMomentumEndEvent.remove(token);
+  }
+
   void ContentSize(winrt::Windows::Foundation::Numerics::float2 const &size) noexcept {
     m_contentSize = size;
     m_contentVisual.Size(size);
@@ -1075,6 +1103,14 @@ struct CompScrollerVisual : winrt::implements<
     m_scrollEndDragEvent(*this, winrt::make<CompScrollPositionChangedArgs>(position));
   }
 
+  void FireScrollMomentumBegin(winrt::Windows::Foundation::Numerics::float2 position) noexcept {
+    m_scrollMomentumBeginEvent(*this, winrt::make<CompScrollPositionChangedArgs>(position));
+  }
+
+  void FireScrollMomentumEnd(winrt::Windows::Foundation::Numerics::float2 position) noexcept {
+    m_scrollMomentumEndEvent(*this, winrt::make<CompScrollPositionChangedArgs>(position));
+  }
+
   void UpdateMaxPosition() noexcept {
     m_interactionTracker.MaxPosition(
         {std::max<float>(m_contentSize.x - m_visualSize.x, 0),
@@ -1263,6 +1299,12 @@ struct CompScrollerVisual : winrt::implements<
   winrt::event<winrt::Windows::Foundation::EventHandler<
       winrt::Microsoft::ReactNative::Composition::Experimental::IScrollPositionChangedArgs>>
       m_scrollEndDragEvent;
+  winrt::event<winrt::Windows::Foundation::EventHandler<
+      winrt::Microsoft::ReactNative::Composition::Experimental::IScrollPositionChangedArgs>>
+      m_scrollMomentumBeginEvent;
+  winrt::event<winrt::Windows::Foundation::EventHandler<
+      winrt::Microsoft::ReactNative::Composition::Experimental::IScrollPositionChangedArgs>>
+      m_scrollMomentumEndEvent;
   typename TTypeRedirects::SpriteVisual m_visual{nullptr};
   typename TTypeRedirects::SpriteVisual m_contentVisual{nullptr};
   typename TTypeRedirects::InteractionTracker m_interactionTracker{nullptr};

vnext/Microsoft.ReactNative/Fabric/Composition/ScrollViewComponentView.cpp

@@ -1354,6 +1354,32 @@ winrt::Microsoft::ReactNative::Composition::Experimental::IVisual ScrollViewComp
         }
       });
 
+  m_scrollMomentumBeginRevoker = m_scrollVisual.ScrollMomentumBegin(
+      winrt::auto_revoke,
+      [this](
+          winrt::IInspectable const & /*sender*/,
+          winrt::Microsoft::ReactNative::Composition::Experimental::IScrollPositionChangedArgs const &args) {
+        auto eventEmitter = GetEventEmitter();
+        if (eventEmitter) {
+          auto scrollMetrics = getScrollMetrics(eventEmitter, args);
+          std::static_pointer_cast<facebook::react::ScrollViewEventEmitter const>(eventEmitter)
+              ->onMomentumScrollBegin(scrollMetrics);
+        }
+      });
+
+  m_scrollMomentumEndRevoker = m_scrollVisual.ScrollMomentumEnd(
+      winrt::auto_revoke,
+      [this](
+          winrt::IInspectable const & /*sender*/,
+          winrt::Microsoft::ReactNative::Composition::Experimental::IScrollPositionChangedArgs const &args) {
+        auto eventEmitter = GetEventEmitter();
+        if (eventEmitter) {
+          auto scrollMetrics = getScrollMetrics(eventEmitter, args);
+          std::static_pointer_cast<facebook::react::ScrollViewEventEmitter const>(eventEmitter)
+              ->onMomentumScrollEnd(scrollMetrics);
+        }
+      });
+
   return visual;
 }
 

vnext/Microsoft.ReactNative/Fabric/Composition/ScrollViewComponentView.h

@@ -148,9 +148,12 @@ struct ScrollInteractionTrackerOwner : public winrt::implements<
       m_scrollPositionChangedRevoker{};
   winrt::Microsoft::ReactNative::Composition::Experimental::IScrollVisual::ScrollBeginDrag_revoker
       m_scrollBeginDragRevoker{};
-
   winrt::Microsoft::ReactNative::Composition::Experimental::IScrollVisual::ScrollEndDrag_revoker
       m_scrollEndDragRevoker{};
+  winrt::Microsoft::ReactNative::Composition::Experimental::IScrollVisual::ScrollMomentumBegin_revoker
+      m_scrollMomentumBeginRevoker{};
+  winrt::Microsoft::ReactNative::Composition::Experimental::IScrollVisual::ScrollMomentumEnd_revoker
+      m_scrollMomentumEndRevoker{};
 
   float m_zoomFactor{1.0f};
   bool m_isScrollingFromInertia = false;