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Editor Scripting - Undo.PerformUndo NullReferenceException

Discussion in 'Immediate Mode GUI (IMGUI)' started by The MC, Jul 7, 2012.

  1. The MC

    The MC

    Joined:
    Oct 31, 2005
    Posts:
    105
    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!
     
  2. xWebber

    xWebber

    Joined:
    Jul 30, 2012
    Posts:
    23
    Same here with OnGUI(). Everything works, but there's this exception..
     
  3. Arkade

    Arkade

    Joined:
    Oct 11, 2012
    Posts:
    621
    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 :)
     
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