Adds option to allow ViewManagers to capture pointer (#8969)

* Adds option to allow ViewManagers to capture pointer

Adds property to ReactPointerEventArgs to allow view managers to capture
the pointer while still allowing RN to emit events to JS. XAML only
allows capturing the pointer on PointerPressed, so this would allow, for
example, a view manager that supports custom native drag behaviors that
have a threshold for action (and when that threshold is not exceeded,
the gesture is handled by RN).

* Change files

change/react-native-windows-1fca69d4-5eb2-4787-91ff-91a19b4fbad9.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "applying package updates ***NO_CI***",
+  "packageName": "react-native-windows",
+  "email": "[email protected]",
+  "dependentChangeType": "patch"
+}

vnext/Microsoft.ReactNative/ReactPointerEventArgs.cpp

@@ -39,6 +39,14 @@ void ReactPointerEventArgs::Target(winrt::IInspectable const &target) noexcept {
   m_target = target;
 }
 
+bool ReactPointerEventArgs::AllowUncaptured() const noexcept {
+  return m_allowUncaptured;
+}
+
+void ReactPointerEventArgs::AllowUncaptured(bool allowUncaptured) noexcept {
+  m_allowUncaptured = allowUncaptured;
+}
+
 ReactPointerEventArgs::ReactPointerEventArgs(
     PointerEventKind kind,
     xaml::Input::PointerRoutedEventArgs const &args) noexcept

vnext/Microsoft.ReactNative/ReactPointerEventArgs.h

@@ -16,13 +16,17 @@ struct ReactPointerEventArgs : ReactPointerEventArgsT<ReactPointerEventArgs> {
   winrt::IInspectable Target() const noexcept;
   void Target(winrt::IInspectable const &target) noexcept;
 
+  bool AllowUncaptured() const noexcept;
+  void AllowUncaptured(bool allowUncaptured) noexcept;
+
   // Internal use
   ReactPointerEventArgs(PointerEventKind kind, xaml::Input::PointerRoutedEventArgs const &args) noexcept;
 
  private:
   PointerEventKind m_kind;
   xaml::Input::PointerRoutedEventArgs const &m_args;
   winrt::IInspectable m_target{nullptr};
+  bool m_allowUncaptured{false};
 };
 
 } // namespace winrt::Microsoft::ReactNative::implementation

vnext/Microsoft.ReactNative/ReactPointerEventArgs.idl

@@ -63,5 +63,17 @@ namespace Microsoft.ReactNative {
       get;
       set;
     };
+    DOC_STRING(
+      "Gets or sets a flag that allows the ReactRootView to handle pointer "
+      "events even when it does not capture the pointer. This is particularly "
+      "useful for view managers that seek to capture the pointer to handle "
+      "move events for a gesture (e.g., dragging), but conditionally may "
+      "allow the ReactRootView to emit events (e.g., if the "
+      "@PointerEventKind.End event is received before a drag threshold is hit."
+    )
+    Boolean AllowUncaptured {
+      get;
+      set;
+    };
   }
 } // namespace Microsoft.ReactNative

vnext/Microsoft.ReactNative/Views/TouchEventHandler.cpp

@@ -119,7 +119,7 @@ void TouchEventHandler::OnPointerPressed(
     return;
   }
 
-  if (m_xamlView.as<xaml::FrameworkElement>().CapturePointer(args.Pointer())) {
+  if (reactArgs.AllowUncaptured() || m_xamlView.as<xaml::FrameworkElement>().CapturePointer(args.Pointer())) {
     assert(!tagsForBranch.empty());
     const auto tag = tagsForBranch.front();