Editor Scripting - Undo.PerformUndo NullReferenceException

Hey Guys,

So I'm experimenting with making my own custom editor tools, and I'm still kind of green on it. I have a tool that automates a bunch of actions on a GameObject for me (changing parent, transformation, rotation, etc). Anyways, I have it set up such that if I hit "Escape" before committing the actions, I would like the scene to perform and Undo and put my selection back the way it was.

Everything "works" per se, however, whenever I hit Escape, I get a NullReferenceException from UnityEditor.SceneView.OnGUI (). The undo still occurs, I just get this error. What's also strange is that if I commit the actions, THEN do a normal "User" undo, everything works fine and I don't get the error.

I make no assumptions that I'm not doing something TERRIBLY stupid, so any and all assistance would be greatly appreciated. Here's my code snippet:

Code (csharp):

1.  
2. public static void OnSceneGUI(SceneView sceneview)
3.     {
4.         Event currentEvent = Event.current;
5.        
6.         // if User hits "escape"
7.         if ( currentEvent.type == EventType.keyDown  currentEvent.keyCode == KeyCode.Escape )
8.         {
9.             // if the user is using a tool, clean up and Undo
10.             if ( window.currentTool > -1  Selection.activeTransform )
11.             {
12.                 currentEvent.Use();
13.                 SelectionCleanup();
14.                 RecallTool();
15.                 ResetToolbar();
16.                 Undo.PerformUndo();
17.             }
18.             // otherwise, just clear the user's selection
19.             else if ( Selection.activeTransform )
20.                 Selection.activeGameObject = null;
21.         }
22. .......
23.  

Here's the error I get:

Code (csharp):

1.  
2. NullReferenceException
3. UnityEditor.SceneView.OnGUI () (at C:/BuildAgent/work/14194e8ce88cdf47/Editor/Mono/SceneView/SceneView.cs:727)
4. System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
5.  

And here's the Editor Log:

Code (csharp):

1.  
2. Unloading 410 unused Assets to reduce memory usage. Loaded Objects now: 981. Operation took 57.267323 ms.
3. System memory in use: 14.9 MB.
4. NullReferenceException
5.   at (wrapper managed-to-native) UnityEditor.Handles:SetCameraFilterMode (UnityEngine.Camera,UnityEditor.Handles/FilterMode)
6.  
7.   at UnityEditor.SceneView.OnGUI () [0x007b7] in C:\BuildAgent\work\14194e8ce88cdf47\Editor\Mono\SceneView\SceneView.cs:727
8.  
9.   at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (object,object[],System.Exception)
10.  
11.   at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
12.  
13. (Filename: C:/BuildAgent/work/14194e8ce88cdf47/Editor/Mono/SceneView/SceneView.cs Line: 727)
14.  

If anyone has any ideas as to what silly mistake I made this time, I'd be grateful for a point in the right direction. Thanks guys!

 

Same here with OnGUI(). Everything works, but there's this exception..

 

Hey, sorry to necro this thread but since I found it while experiencing the same problem and then found an answer, I thought I'd leave it here to help the next traveller!

The answer:

EditorApplication.delayCall

The problem seems to be that we've issued an action in the Scene View but then change things such that it ends up redrawing and having a problem. (What's often called a reentrancy problem I believe.) So defer the code that's changing things to later and it avoids the problem. I was literally writing a level building tool too and hit the same problem -- mine was moving mouse out of the scene and doing Undo. It had all worked without undo but once I added that, I think the Undo is requesting a redraw and thus hitting the lack of reentrant safety. Just my guess.

HTH