Fix crash when removing Anim Event visual script that is used in opened Animation timeline

#2471

Source/Editor/Content/Items/VisualScriptItem.cs

@@ -249,6 +249,7 @@ namespace FlaxEditor.Content
         private ScriptMemberInfo[] _parameters;
         private ScriptMemberInfo[] _methods;
         private object[] _attributes;
+        private List<Action<ScriptType>> _disposing;
 
         /// <summary>
         /// Gets the Visual Script asset that contains this type.
@@ -310,6 +311,13 @@ namespace FlaxEditor.Content
 
         internal void Dispose()
         {
+            if (_disposing != null)
+            {
+                foreach (var e in _disposing)
+                    e(new ScriptType(this));
+                _disposing.Clear();
+                _disposing = null;
+            }
             if (_parameters != null)
             {
                 OnAssetReloading(_asset);
@@ -510,6 +518,14 @@ namespace FlaxEditor.Content
             }
             return _methods;
         }
+
+        /// <inheritdoc />
+        public void TrackLifetime(Action<ScriptType> disposing)
+        {
+            if (_disposing == null)
+                _disposing = new List<Action<ScriptType>>();
+            _disposing.Add(disposing);
+        }
     }
 
     /// <summary>

Source/Editor/GUI/Timeline/Tracks/AnimationEventTrack.cs

@@ -99,6 +99,7 @@ namespace FlaxEditor.GUI.Timeline.Tracks
             if (Type == ScriptType.Null)
             {
                 Editor.LogError("Missing anim event type " + _instanceTypeName);
+                InitMissing();
                 return;
             }
             Instance = (AnimEvent)Type.CreateInstance();
@@ -125,20 +126,37 @@ namespace FlaxEditor.GUI.Timeline.Tracks
                 _isRegisteredForScriptsReload = true;
                 ScriptsBuilder.ScriptsReloadBegin += OnScriptsReloadBegin;
             }
+            Type.TrackLifetime(OnTypeDisposing);
+        }
+
+        private void OnTypeDisposing(ScriptType type)
+        {
+            if (Type == type && !IsDisposing)
+            {
+                // Turn into missing script
+                OnScriptsReloadBegin();
+                ScriptsBuilder.ScriptsReloadEnd -= OnScriptsReloadEnd;
+                InitMissing();
+            }
+        }
+
+        private void InitMissing()
+        {
+            CanDelete = true;
+            CanSplit = false;
+            CanResize = false;
+            TooltipText = $"Missing Anim Event Type '{_instanceTypeName}'";
+            BackgroundColor = Color.Red;
+            Type = ScriptType.Null;
+            Instance = null;
         }
 
         internal void InitMissing(string typeName, byte[] data)
         {
-            Type = ScriptType.Null;
             IsContinuous = false;
-            CanDelete = true;
-            CanSplit = false;
-            CanResize = false;
-            TooltipText = $"Missing Anim Event Type '{typeName}'";
-            Instance = null;
-            BackgroundColor = Color.Red;
             _instanceTypeName = typeName;
             _instanceData = data;
+            InitMissing();
         }
 
         internal void Load(BinaryReader stream)

Source/Editor/Scripting/ScriptType.Custom.cs

@@ -144,5 +144,11 @@ namespace FlaxEditor.Scripting
         {
             return Utils.GetEmptyArray<ScriptMemberInfo>();
         }
+
+        /// <inheritdoc />
+        public void TrackLifetime(Action<ScriptType> disposing)
+        {
+            ElementType.TrackLifetime(disposing);
+        }
     }
 }

Source/Editor/Scripting/ScriptType.Interfaces.cs

@@ -167,6 +167,12 @@ namespace FlaxEditor.Scripting
         /// <param name="bindingAttr">A bitmask comprised of one or more <see cref="T:System.Reflection.BindingFlags" /> that specify how the search is conducted.-or- Zero (<see cref="F:System.Reflection.BindingFlags.Default" />), to return an empty array.</param>
         /// <returns>An array of member objects representing all methods defined for the current type that match the specified binding constraints.-or- An empty array of type member, if no methods are defined for the current type, or if none of the defined methods match the binding constraints.</returns>
         ScriptMemberInfo[] GetMethods(BindingFlags bindingAttr);
+
+        /// <summary>
+        /// Registers delegate to be invoked upon script type disposal (except hot-reload in Editor via <see cref="ScriptsBuilder.ScriptsReload"/>). For example, can happen when user deleted Visual Script asset.
+        /// </summary>
+        /// <param name="disposing">Event to call when script type gets disposed (eg. removed asset).</param>
+        void TrackLifetime(Action<ScriptType> disposing);
     }
 
     /// <summary>

Source/Editor/Scripting/ScriptType.cs

@@ -1395,11 +1395,21 @@ namespace FlaxEditor.Scripting
         }
 
         /// <summary>
-        /// Basic check to see if a type could be casted to another type
+        /// Registers delegate to be invoked upon script type disposal (except hot-reload in Editor via <see cref="ScriptsBuilder.ScriptsReload"/>). For example, can happen when user deleted Visual Script asset.
+        /// </summary>
+        /// <param name="disposing">Event to call when script type gets disposed (eg. removed asset).</param>
+        public void TrackLifetime(Action<ScriptType> disposing)
+        {
+            if (_custom != null)
+                _custom.TrackLifetime(disposing);
+        }
+
+        /// <summary>
+        /// Basic check to see if a type could be cast to another type
         /// </summary>
         /// <param name="from">Source type</param>
         /// <param name="to">Target type</param>
-        /// <returns>True if the type can be casted</returns>
+        /// <returns>True if the type can be cast.</returns>
         public static bool CanCast(ScriptType from, ScriptType to)
         {
             if (from == to)
@@ -1412,10 +1422,10 @@ namespace FlaxEditor.Scripting
         }
 
         /// <summary>
-        /// Basic check to see if this type could be casted to another type
+        /// Basic check to see if this type could be cast to another type
         /// </summary>
         /// <param name="to">Target type</param>
-        /// <returns>True if the type can be casted</returns>
+        /// <returns>True if the type can be cast.</returns>
         public bool CanCastTo(ScriptType to)
         {
             return CanCast(this, to);

Source/Editor/Surface/Archetypes/BehaviorTree.cs

@@ -104,6 +104,16 @@ namespace FlaxEditor.Surface.Archetypes
                 }
             }
 
+            private void OnTypeDisposing(ScriptType type)
+            {
+                if (_type == type && !IsDisposing)
+                {
+                    // Turn into missing script
+                    _type = ScriptType.Null;
+                    Instance = null;
+                }
+            }
+
             public override void OnLoaded(SurfaceNodeActions action)
             {
                 base.OnLoaded(action);
@@ -113,6 +123,7 @@ namespace FlaxEditor.Surface.Archetypes
                 _type = TypeUtils.GetType(typeName);
                 if (_type != null)
                 {
+                    _type.TrackLifetime(OnTypeDisposing);
                     TooltipText = Editor.Instance.CodeDocs.GetTooltip(_type);
                     try
                     {