Hello,
this is probably my first post here, even if I read the forum quite often.
I’m working on an animator controller and I have an issue that doesn’t allow me to work properly. When I am on an animation transition to Exit and I want to preview the destination to a BlendTree, I can’t display the BlendTree parameter.
And in the console I get a related error that is:
ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
I found a tracked issue that seems to be the same here.
Maybe @Mecanim-Dev , you can help me 
Thanks!
nobody experienced the same issue?
@Mecanim-Dev can you please give me some info about it?
It is incredible that choosing the right values for a transition that goes from a single animation state to a blend-tree is a guesstimation process due to this annoying bug.
Is it planned any fix? It does not seem to be a little bug but an important issue to fix.
Hi @marcomusto
Thanks for the report.
So we did investigate this issue yesterday, and it only happen when you want to preview a transition that goes from an animationstate throught the exit state to a blend tree.
Transition preview from an animation state to a blend tree is working as expected.
We will fix this in the upcoming weeks in 2020.1 and depending if the fix is not to complex we will backport it to 2019.x.
Best regards.
Hey, I get massive loads of this error:
ArgumentOutOfRangeException: Length cannot be less than zero.
Parameter name: length
System.String.Substring (System.Int32 startIndex, System.Int32 length) (at :0)
UnityEditor.Graphs.AnimationBlendTree.GraphGUI.LimitStringWidth (System.String content, System.Single width, UnityEngine.GUIStyle style)
Continues
(at /Users/builduser/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/AnimationBlendTree/GraphGUI.cs:68)
UnityEditor.Graphs.AnimationBlendTree.GraphGUI.OnGraphGUI () (at /Users/builduser/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/AnimationBlendTree/GraphGUI.cs:184)
UnityEditor.Graphs.AnimatorControllerTool.BlendTreeView (UnityEngine.Rect position, System.Single zoomLevel) (at /Users/builduser/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:1931)
UnityEditor.Graphs.AnimatorControllerTool.DoGraph (UnityEngine.Rect graphRect, System.Single zoomLevel) (at /Users/builduser/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:1310)
UnityEditor.Graphs.AnimatorControllerTool.b__141_11 () (at /Users/builduser/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:1731)
UnityEditor.Graphs.AnimatorControllerTool.ScopedOnGUI (System.Action onGUIHandler) (at /Users/builduser/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:1491)
UnityEditor.Graphs.AnimatorControllerTool.b__141_9 () (at /Users/builduser/buildslave/unity/build/Editor/Graphs/UnityEditor.Graphs/Animation/AnimatorControllerTool.cs:1728)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:293)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, UnityEngine.Matrix4x4 worldTransform, UnityEngine.Rect clippingRect, System.Action onGUIHandler, System.Boolean canAffectFocus) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:508)
UnityEngine.UIElements.IMGUIContainer.DoIMGUIRepaint () (at /Users/builduser/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:463)
UnityEngine.UIElements.UIR.RenderChainCommand.ExecuteNonDrawMesh (UnityEngine.UIElements.UIR.DrawParams drawParams, System.Boolean straightY, System.Single pixelsPerPoint, System.Exception& immediateException) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Renderer/UIRenderer/UIRenderers.cs:107)
Rethrow as ImmediateModeException
UnityEngine.UIElements.UIR.RenderChain.Render (UnityEngine.Rect viewport, UnityEngine.Matrix4x4 projection, UnityEngine.UIElements.PanelClearFlags clearFlags) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Renderer/UIRChainBuilder.cs:392)
UnityEngine.UIElements.UIRRepaintUpdater.DrawChain (UnityEngine.Rect viewport, UnityEngine.Matrix4x4 projection) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Renderer/UIRRepaintUpdater.cs:68)
UnityEngine.UIElements.UIRRepaintUpdater.Update () (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Renderer/UIRRepaintUpdater.cs:57)
UnityEngine.UIElements.VisualTreeUpdater.UpdateVisualTreePhase (UnityEngine.UIElements.VisualTreeUpdatePhase phase) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/VisualTreeUpdater.cs:84)
UnityEngine.UIElements.Panel.UpdateForRepaint () (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Panel.cs:721)
UnityEngine.UIElements.Panel.Repaint (UnityEngine.Event e) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Panel.cs:747)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/UIElementsUtility.bindings.cs:387)
UnityEngine.UIElements.UIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/UIElementsUtility.bindings.cs:194)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at /Users/builduser/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:197)
Problem appears when I work on Blend Tree. I updated Unity to latest version but it didn’t help. I don’t know if this is related or if it is problem of its own but my Blend tree graph also disappears. It shows only the blank grid.
I am a complete beginner on this.
I solved my problem by switching to Godot.
