Fix missing UICanvas linkage in prefab preview

#218

Source/Engine/UI/UICanvas.cpp

@@ -15,6 +15,7 @@ MMethod* UICanvas_PostDeserialize = nullptr;
 MMethod* UICanvas_OnEnable = nullptr;
 MMethod* UICanvas_OnDisable = nullptr;
 MMethod* UICanvas_EndPlay = nullptr;
+MMethod* UICanvas_ParentChanged = nullptr;
 
 #define UICANVAS_INVOKE(event) \
     auto instance = GetManagedInstance(); \
@@ -43,6 +44,7 @@ UICanvas::UICanvas(const SpawnParams& params)
         UICanvas_OnEnable = mclass->GetMethod("OnEnable");
         UICanvas_OnDisable = mclass->GetMethod("OnDisable");
         UICanvas_EndPlay = mclass->GetMethod("EndPlay");
+        UICanvas_ParentChanged = mclass->GetMethod("ParentChanged");
     }
 }
 
@@ -133,6 +135,14 @@ void UICanvas::EndPlay()
     Actor::EndPlay();
 }
 
+void UICanvas::OnParentChanged()
+{
+    // Base
+    Actor::OnParentChanged();
+
+    UICANVAS_INVOKE(ParentChanged);
+}
+
 void UICanvas::OnEnable()
 {
     UICANVAS_INVOKE(OnEnable);

Source/Engine/UI/UICanvas.cs

@@ -539,6 +539,16 @@ namespace FlaxEngine
             Setup();
         }
 
+        internal void ParentChanged()
+        {
+#if FLAX_EDITOR
+            if (RenderMode == CanvasRenderMode.ScreenSpace && _editorRoot != null && _guiRoot != null)
+            {
+                _guiRoot.Parent = HasParent ? _editorRoot : null;
+            }
+#endif
+        }
+
         internal void OnEnable()
         {
 #if FLAX_EDITOR
@@ -587,6 +597,8 @@ namespace FlaxEngine
 
         internal void EditorOverride(SceneRenderTask task, ContainerControl root)
         {
+            if (_editorTask == task && _editorRoot == root)
+                return;
             if (_editorTask != null && _renderer != null)
                 _editorTask.CustomPostFx.Remove(_renderer);
             if (_editorRoot != null && _guiRoot != null)

Source/Engine/UI/UICanvas.h

@@ -24,6 +24,7 @@ protected:
     // [Actor]
     void BeginPlay(SceneBeginData* data) final override;
     void EndPlay() final override;
+    void OnParentChanged() override;
     void OnEnable() override;
     void OnDisable() override;
     void OnTransformChanged() final override;