Fix GUI traversal during child removal

Source/Engine/Tests/TestContainerControl.cs

@@ -26,6 +26,29 @@ namespace FlaxEngine.Tests
             }
         }
 
+        private sealed class RemovingControl : MyControl
+        {
+            private readonly Control[] _controlsToRemove;
+
+            public RemovingControl(float x, float y, float width, float height, params Control[] controlsToRemove)
+            : base(x, y, width, height)
+            {
+                _controlsToRemove = controlsToRemove;
+            }
+
+            public override void OnMouseEnter(Float2 location)
+            {
+                for (int i = 0; i < _controlsToRemove.Length; i++)
+                {
+                    var control = _controlsToRemove[i];
+                    if (control.Parent == Parent)
+                        control.Parent = null;
+                }
+
+                base.OnMouseEnter(location);
+            }
+        }
+
         [Test]
         public void TestChildren()
         {
@@ -53,6 +76,25 @@ namespace FlaxEngine.Tests
             Assert.AreEqual(cc1.GetChildAt(new Vector2(15, 5)), cc2);
             Assert.AreEqual(cc1.GetChildAtRecursive(new Vector2(35, 25)), c3);
         }
+
+        [Test]
+        public void TestMouseMoveAllowsChildrenRemoval()
+        {
+            var container = new MyContainerControl(0, 0, 100, 100);
+            var first = new MyControl(0, 0, 100, 100);
+            var second = new MyControl(0, 0, 100, 100);
+            var removing = new RemovingControl(0, 0, 100, 100, first, second);
+            container.AddChild(first);
+            container.AddChild(second);
+            container.AddChild(removing);
+
+            // The top-most child removes multiple siblings during input dispatch.
+            // Traversal must not use the now-stale next index.
+            container.OnMouseMove(new Float2(50, 50));
+
+            Assert.AreEqual(1, container.ChildrenCount);
+            Assert.AreEqual(removing, container.GetChild(0));
+        }
     }
 }
 #endif

Source/Engine/UI/GUI/ContainerControl.cs

@@ -910,7 +910,7 @@ namespace FlaxEngine.GUI
                     return false;
                 }
             }
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible)
@@ -928,7 +928,7 @@ namespace FlaxEngine.GUI
         public override void OnMouseEnter(Float2 location)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -948,7 +948,7 @@ namespace FlaxEngine.GUI
         public override void OnMouseMove(Float2 location)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -998,7 +998,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseWheel(Float2 location, float delta)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1019,7 +1019,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseDown(Float2 location, MouseButton button)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1040,7 +1040,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseUp(Float2 location, MouseButton button)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1061,7 +1061,7 @@ namespace FlaxEngine.GUI
         public override bool OnMouseDoubleClick(Float2 location, MouseButton button)
         {
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1096,7 +1096,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override void OnTouchEnter(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled && !child.IsTouchPointerOver(pointerId))
@@ -1114,7 +1114,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override bool OnTouchDown(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1139,7 +1139,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override void OnTouchMove(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1168,7 +1168,7 @@ namespace FlaxEngine.GUI
         /// <inheritdoc />
         public override bool OnTouchUp(Float2 location, int pointerId)
         {
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled && child.IsTouchPointerOver(pointerId))
@@ -1250,7 +1250,7 @@ namespace FlaxEngine.GUI
             var result = base.OnDragEnter(ref location, data);
 
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1275,7 +1275,7 @@ namespace FlaxEngine.GUI
             var result = base.OnDragMove(ref location, data);
 
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)
@@ -1333,7 +1333,7 @@ namespace FlaxEngine.GUI
             var result = base.OnDragDrop(ref location, data);
 
             // Check all children collisions with mouse and fire events for them
-            for (int i = _children.Count - 1; i >= 0 && _children.Count > 0; i--)
+            for (int i = _children.Count - 1; i >= 0 && i < _children.Count; i--)
             {
                 var child = _children[i];
                 if (child.Visible && child.Enabled)