Fixed 'OnDrop' event not called when 'IPointerDownHandler' is also listened. (#1988)

Author: bmalrat

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -16,6 +16,7 @@ however, it has to be formatted properly to pass verification tests.
 - Fixed InputDeviceTester sample only visualizing a given touch contact once. [ISXB-1017](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1017)
 - Fixed an update loop in the asset editor that occurs when selecting an Action Map that has no Actions.
 - Fixed Package compilation when Unity Analytics module is not enabled on 2022.3. [ISXB-996](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-996)
+- Fixed 'OnDrop' event not called when 'IPointerDownHandler' is also listened. [ISXB-1014](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1014)
 
 ### Added
 - Added Hinge Angle sensor support for foldable devices.

Packages/com.unity.inputsystem/InputSystem/Plugins/UI/InputSystemUIInputModule.cs

@@ -496,10 +496,12 @@ private void ProcessPointerButton(ref PointerModel.ButtonState button, PointerEv
                 // Invoke OnPointerDown, if present.
                 var newPressed = ExecuteEvents.ExecuteHierarchy(currentOverGo, eventData, ExecuteEvents.pointerDownHandler);
 
+                var pointerClickHandler = ExecuteEvents.GetEventHandler<IPointerClickHandler>(currentOverGo);
+
                 // If no GO responded to OnPointerDown, look for one that responds to OnPointerClick.
                 // NOTE: This only looks up the handler. We don't invoke OnPointerClick here.
                 if (newPressed == null)
-                    newPressed = ExecuteEvents.GetEventHandler<IPointerClickHandler>(currentOverGo);
+                    newPressed = pointerClickHandler;
 
                 // Reset click state if delay to last release was too long or if we didn't
                 // press on the same object as last time. The latter part we don't know until
@@ -515,7 +517,7 @@ private void ProcessPointerButton(ref PointerModel.ButtonState button, PointerEv
                 // become null.
                 eventData.pointerPress = newPressed;
                 #if UNITY_2020_1_OR_NEWER // pointerClick doesn't exist before this.
-                eventData.pointerClick = ExecuteEvents.GetEventHandler<IPointerClickHandler>(currentOverGo);
+                eventData.pointerClick = pointerClickHandler;
                 #endif
                 eventData.rawPointerPress = currentOverGo;
 
@@ -538,9 +540,9 @@ private void ProcessPointerButton(ref PointerModel.ButtonState button, PointerEv
                 //          click and OnPointerClick is thus never invoked.
                 var pointerClickHandler = ExecuteEvents.GetEventHandler<IPointerClickHandler>(currentOverGo);
                 #if UNITY_2020_1_OR_NEWER
-                var isClick = eventData.pointerClick == pointerClickHandler && eventData.eligibleForClick;
+                var isClick = eventData.pointerClick != null && eventData.pointerClick == pointerClickHandler && eventData.eligibleForClick;
                 #else
-                var isClick = eventData.pointerPress == pointerClickHandler && eventData.eligibleForClick;
+                var isClick = eventData.pointerPress != null && eventData.pointerPress == pointerClickHandler && eventData.eligibleForClick;
                 #endif
                 if (isClick)
                 {