FIX: UI Click events passing down to child objects (ISXB-857) (#1911)

* FIX: UI Click events passing down to child objects (ISXB-857)

* Guard usages of pointerClick to 2020.1, when it was added.

Author: graham-huws

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -23,6 +23,7 @@ however, it has to be formatted properly to pass verification tests.
 - Fixed DualSense Edge's vibration and light bar not working on Windows
 - Fixed Project-wide Actions asset failing to reload properly after deleting project's Library folder.
 - Fixed an issue where `System.InvalidOperationException` is thrown when entering PlayMode after deleting an ActionMap from Project-wide actions and later resetting it.
+- Fixed OnPointerClick events not propagating to child objects unless the child also handled OnPointerDown events [ISXB-857](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-857).
 - Fixed Input Actions Editor window resource leak that could result in unexpected exceptions [ISXB-865](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-865).
 - Fixed an issue where UI integration would throw exceptions when Project-wide Input Actions asset did not contain the implicitly required `UI` action map or was missing any of the required actions. Additionally this fix now also generates warnings in the console for any divergence from expected action configuration or lack of bindings in edit-mode.
 

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

@@ -496,6 +496,9 @@ private void ProcessPointerButton(ref PointerModel.ButtonState button, PointerEv
                 // Set pointerPress. This nukes lastPress. Meaning that after OnPointerDown, lastPress will
                 // become null.
                 eventData.pointerPress = newPressed;
+                #if UNITY_2020_1_OR_NEWER // pointerClick doesn't exist before this.
+                eventData.pointerClick = ExecuteEvents.GetEventHandler<IPointerClickHandler>(currentOverGo);
+                #endif
                 eventData.rawPointerPress = currentOverGo;
 
                 // Save the drag handler for drag events during this mouse down.
@@ -516,7 +519,11 @@ private void ProcessPointerButton(ref PointerModel.ButtonState button, PointerEv
                 //       2) StandaloneInputModule increases click counts even if something is eventually not deemed a
                 //          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;
+                #else
                 var isClick = eventData.pointerPress == pointerClickHandler && eventData.eligibleForClick;
+                #endif
                 if (isClick)
                 {
                     // Count clicks.
@@ -539,7 +546,11 @@ private void ProcessPointerButton(ref PointerModel.ButtonState button, PointerEv
 
                 // Invoke OnPointerClick or OnDrop.
                 if (isClick)
+                    #if UNITY_2020_1_OR_NEWER
+                    ExecuteEvents.Execute(eventData.pointerClick, eventData, ExecuteEvents.pointerClickHandler);
+                    #else
                     ExecuteEvents.Execute(eventData.pointerPress, eventData, ExecuteEvents.pointerClickHandler);
+                    #endif
                 else if (eventData.dragging && eventData.pointerDrag != null)
                     ExecuteEvents.ExecuteHierarchy(currentOverGo, eventData, ExecuteEvents.dropHandler);