Fix ScreenSpace UICanvas prefab preview activate/deactivate

Source/Engine/UI/UICanvas.cpp

@@ -14,6 +14,9 @@ MMethod* UICanvas_Deserialize = nullptr;
 MMethod* UICanvas_PostDeserialize = nullptr;
 MMethod* UICanvas_OnEnable = nullptr;
 MMethod* UICanvas_OnDisable = nullptr;
+#if USE_EDITOR
+MMethod* UICanvas_OnActiveInTreeChanged = nullptr;
+#endif
 MMethod* UICanvas_EndPlay = nullptr;
 MMethod* UICanvas_ParentChanged = nullptr;
 
@@ -43,6 +46,9 @@ UICanvas::UICanvas(const SpawnParams& params)
         UICanvas_PostDeserialize = mclass->GetMethod("PostDeserialize");
         UICanvas_OnEnable = mclass->GetMethod("OnEnable");
         UICanvas_OnDisable = mclass->GetMethod("OnDisable");
+#if USE_EDITOR
+        UICanvas_OnActiveInTreeChanged = mclass->GetMethod("OnActiveInTreeChanged");
+#endif
         UICanvas_EndPlay = mclass->GetMethod("EndPlay");
         UICanvas_ParentChanged = mclass->GetMethod("ParentChanged");
     }
@@ -167,3 +173,15 @@ void UICanvas::OnTransformChanged()
     _box = BoundingBox(_transform.Translation);
     _sphere = BoundingSphere(_transform.Translation, 0.0f);
 }
+
+#if USE_EDITOR
+
+void UICanvas::OnActiveInTreeChanged()
+{
+    UICANVAS_INVOKE(OnActiveInTreeChanged);
+
+    // Base
+    Actor::OnActiveInTreeChanged();
+}
+
+#endif

Source/Engine/UI/UICanvas.cs

@@ -672,6 +672,16 @@ namespace FlaxEngine
             }
         }
 
+#if FLAX_EDITOR
+        internal void OnActiveInTreeChanged()
+        {
+            if (RenderMode == CanvasRenderMode.ScreenSpace && _editorRoot != null && _guiRoot != null)
+            {
+                _guiRoot.Parent = IsActiveInHierarchy ? _editorRoot : null;
+            }
+        }
+#endif
+
         internal void EndPlay()
         {
             if (_isRegisteredForTick)

Source/Engine/UI/UICanvas.h

@@ -28,4 +28,7 @@ protected:
     void OnEnable() override;
     void OnDisable() override;
     void OnTransformChanged() final override;
+#if USE_EDITOR
+    void OnActiveInTreeChanged() override;
+#endif
 };