Fixed panel collection change actions.

As suggested in #1286

src/Avalonia.Base/Collections/IAvaloniaList.cs

@@ -36,6 +36,21 @@ namespace Avalonia.Collections
         /// <param name="items">The items.</param>
         void InsertRange(int index, IEnumerable<T> items);
 
+        /// <summary>
+        /// Moves an item to a new index.
+        /// </summary>
+        /// <param name="oldIndex">The index of the item to move.</param>
+        /// <param name="newIndex">The index to move the item to.</param>
+        void Move(int oldIndex, int newIndex);
+
+        /// <summary>
+        /// Moves multiple items to a new index.
+        /// </summary>
+        /// <param name="oldIndex">The first index of the items to move.</param>
+        /// <param name="count">The number of items to move.</param>
+        /// <param name="newIndex">The index to move the items to.</param>
+        void MoveRange(int oldIndex, int count, int newIndex);
+
         /// <summary>
         /// Removes multiple items from the collection.
         /// </summary>

src/Avalonia.Controls/Panel.cs

@@ -115,6 +115,11 @@ namespace Avalonia.Controls
                     VisualChildren.AddRange(e.NewItems.OfType<Visual>());
                     break;
 
+                case NotifyCollectionChangedAction.Move:
+                    LogicalChildren.MoveRange(e.OldStartingIndex, e.OldItems.Count, e.NewStartingIndex);
+                    VisualChildren.MoveRange(e.OldStartingIndex, e.OldItems.Count, e.NewStartingIndex);
+                    break;
+
                 case NotifyCollectionChangedAction.Remove:
                     controls = e.OldItems.OfType<Control>().ToList();
                     LogicalChildren.RemoveAll(controls);
@@ -132,11 +137,7 @@ namespace Avalonia.Controls
                     break;
 
                 case NotifyCollectionChangedAction.Reset:
-                    controls = e.OldItems.OfType<Control>().ToList();
-                    LogicalChildren.Clear();
-                    VisualChildren.Clear();
-                    VisualChildren.AddRange(_children);
-                    break;
+                    throw new NotSupportedException();
             }
 
             InvalidateMeasure();

src/Avalonia.Visuals/Visual.cs

@@ -537,6 +537,19 @@ namespace Avalonia
                         v.SetVisualParent(null);
                     }
 
+                    break;
+
+                case NotifyCollectionChangedAction.Replace:
+                    foreach (Visual v in e.OldItems)
+                    {
+                        v.SetVisualParent(null);
+                    }
+
+                    foreach (Visual v in e.NewItems)
+                    {
+                        v.SetVisualParent(this);
+                    }
+
                     break;
             }
         }

tests/Avalonia.Controls.UnitTests/PanelTests.cs

@@ -4,6 +4,7 @@
 using System.Linq;
 using Avalonia.Collections;
 using Avalonia.LogicalTree;
+using Avalonia.VisualTree;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests
@@ -18,8 +19,9 @@ namespace Avalonia.Controls.UnitTests
 
             panel.Children.Add(child);
 
-            Assert.Equal(child.Parent, panel);
-            Assert.Equal(child.GetLogicalParent(), panel);
+            Assert.Same(child.Parent, panel);
+            Assert.Same(child.GetLogicalParent(), panel);
+            Assert.Same(child.GetVisualParent(), panel);
         }
 
         [Fact]
@@ -45,6 +47,7 @@ namespace Avalonia.Controls.UnitTests
 
             Assert.Null(child.Parent);
             Assert.Null(child.GetLogicalParent());
+            Assert.Null(child.GetVisualParent());
         }
 
         [Fact]
@@ -60,8 +63,10 @@ namespace Avalonia.Controls.UnitTests
 
             Assert.Null(child1.Parent);
             Assert.Null(child1.GetLogicalParent());
+            Assert.Null(child1.GetVisualParent());
             Assert.Null(child2.Parent);
             Assert.Null(child2.GetLogicalParent());
+            Assert.Null(child2.GetVisualParent());
         }
 
         [Fact]
@@ -77,24 +82,32 @@ namespace Avalonia.Controls.UnitTests
 
             Assert.Null(child1.Parent);
             Assert.Null(child1.GetLogicalParent());
+            Assert.Null(child1.GetVisualParent());
             Assert.Null(child2.Parent);
             Assert.Null(child2.GetLogicalParent());
+            Assert.Null(child2.GetVisualParent());
         }
 
         [Fact]
-        public void Setting_Children_Should_Make_Controls_Appear_In_Panel_Children()
+        public void Replacing_Panel_Children_Should_Clear_And_Set_Control_Parent()
         {
             var panel = new Panel();
-            var child = new Control();
+            var child1 = new Control();
+            var child2 = new Control();
 
-            panel.Children = new Controls { child };
+            panel.Children.Add(child1);
+            panel.Children[0] = child2;
 
-            Assert.Equal(new[] { child }, panel.Children);
-            Assert.Equal(new[] { child }, panel.GetLogicalChildren());
+            Assert.Null(child1.Parent);
+            Assert.Null(child1.GetLogicalParent());
+            Assert.Null(child1.GetVisualParent());
+            Assert.Same(child2.Parent, panel);
+            Assert.Same(child2.GetLogicalParent(), panel);
+            Assert.Same(child2.GetVisualParent(), panel);
         }
 
         [Fact]
-        public void Child_Control_Should_Appear_In_Panel_Children()
+        public void Child_Control_Should_Appear_In_Panel_Logical_And_Visual_Children()
         {
             var panel = new Panel();
             var child = new Control();
@@ -103,10 +116,11 @@ namespace Avalonia.Controls.UnitTests
 
             Assert.Equal(new[] { child }, panel.Children);
             Assert.Equal(new[] { child }, panel.GetLogicalChildren());
+            Assert.Equal(new[] { child }, panel.GetVisualChildren());
         }
 
         [Fact]
-        public void Removing_Child_Control_Should_Remove_From_Panel_Children()
+        public void Removing_Child_Control_Should_Remove_From_Panel_Logical_And_Visual_Children()
         {
             var panel = new Panel();
             var child = new Control();
@@ -115,7 +129,36 @@ namespace Avalonia.Controls.UnitTests
             panel.Children.Remove(child);
 
             Assert.Equal(new Control[0], panel.Children);
-            Assert.Equal(new ILogical[0], panel.GetLogicalChildren());
+            Assert.Empty(panel.GetLogicalChildren());
+            Assert.Empty(panel.GetVisualChildren());
+        }
+
+        [Fact]
+        public void Moving_Panel_Children_Should_Reoder_Logical_And_Visual_Children()
+        {
+            var panel = new Panel();
+            var child1 = new Control();
+            var child2 = new Control();
+
+            panel.Children.Add(child1);
+            panel.Children.Add(child2);
+            panel.Children.Move(1, 0);
+
+            Assert.Equal(new[] { child2, child1 }, panel.GetLogicalChildren());
+            Assert.Equal(new[] { child2, child1 }, panel.GetVisualChildren());
+        }
+
+        [Fact]
+        public void Setting_Children_Should_Make_Controls_Appear_In_Logical_And_Visual_Children()
+        {
+            var panel = new Panel();
+            var child = new Control();
+
+            panel.Children = new Controls { child };
+
+            Assert.Equal(new[] { child }, panel.Children);
+            Assert.Equal(new[] { child }, panel.GetLogicalChildren());
+            Assert.Equal(new[] { child }, panel.GetVisualChildren());
         }
     }
 }