Allow binding container IsVisible with virtualization. (#14276)

Use `SetCurrentValue` to update the container `IsVisible` state when realizing and recycling so that the visible state can be bound.

Fixes #13991

src/Avalonia.Controls/VirtualizingStackPanel.cs

@@ -629,7 +629,7 @@ namespace Avalonia.Controls
                 generator.ItemContainerPrepared(controlItem, item, index);
             }
 
-            controlItem.IsVisible = true;
+            controlItem.SetCurrentValue(Visual.IsVisibleProperty, true);
             return controlItem;
         }
 
@@ -645,7 +645,7 @@ namespace Avalonia.Controls
             if (_recyclePool?.TryGetValue(recycleKey, out var recyclePool) == true && recyclePool.Count > 0)
             {
                 var recycled = recyclePool.Pop();
-                recycled.IsVisible = true;
+                recycled.SetCurrentValue(Visual.IsVisibleProperty, true);
                 generator.PrepareItemContainer(recycled, item, index);
                 generator.ItemContainerPrepared(recycled, item, index);
                 return recycled;
@@ -684,7 +684,7 @@ namespace Avalonia.Controls
             }
             else if (recycleKey == s_itemIsItsOwnContainer)
             {
-                element.IsVisible = false;
+                element.SetCurrentValue(Visual.IsVisibleProperty, false);
             }
             else if (KeyboardNavigation.GetTabOnceActiveElement(ItemsControl) == element)
             {
@@ -695,7 +695,7 @@ namespace Avalonia.Controls
             {
                 ItemContainerGenerator!.ClearItemContainer(element);
                 PushToRecyclePool(recycleKey, element);
-                element.IsVisible = false;
+                element.SetCurrentValue(Visual.IsVisibleProperty, false);
             }
         }
 
@@ -713,7 +713,7 @@ namespace Avalonia.Controls
             {
                 ItemContainerGenerator!.ClearItemContainer(element);
                 PushToRecyclePool(recycleKey, element);
-                element.IsVisible = false;
+                element.SetCurrentValue(Visual.IsVisibleProperty, false);
             }
         }
 

tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs

@@ -1048,6 +1048,74 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(new(0, 200), scroll.Offset);
         }
 
+        [Fact]
+        public void Can_Bind_Item_IsVisible()
+        {
+            using var app = App();
+            var style = CreateIsVisibleBindingStyle();            
+            var items = Enumerable.Range(0, 100).Select(x => new ItemWithIsVisible(x)).ToList();
+            var (target, scroll, itemsControl) = CreateTarget(items: items, styles: new[] { style });
+            var container = target.ContainerFromIndex(2)!;
+
+            Assert.True(container.IsVisible);
+            Assert.Equal(20, container.Bounds.Top);
+
+            items[2].IsVisible = false;
+            Layout(target);
+
+            Assert.False(container.IsVisible);
+
+            // Next container should be in correct position.
+            Assert.Equal(20, target.ContainerFromIndex(3)!.Bounds.Top);
+        }
+
+        [Fact]
+        public void IsVisible_Binding_Persists_After_Scrolling()
+        {
+            using var app = App();
+            var style = CreateIsVisibleBindingStyle();
+            var items = Enumerable.Range(0, 100).Select(x => new ItemWithIsVisible(x)).ToList();
+            var (target, scroll, itemsControl) = CreateTarget(items: items, styles: new[] { style });
+            var container = target.ContainerFromIndex(2)!;
+
+            Assert.True(container.IsVisible);
+            Assert.Equal(20, container.Bounds.Top);
+
+            items[2].IsVisible = false;
+            scroll.Offset = new Vector(0, 200);
+            Layout(target);
+
+            scroll.Offset = new Vector(0, 0);
+            Layout(target);
+
+            container = target.ContainerFromIndex(2)!;
+            Assert.False(container.IsVisible);
+        }
+
+        [Fact]
+        public void Recycling_A_Hidden_Control_Shows_It()
+        {
+            using var app = App();
+            var style = CreateIsVisibleBindingStyle();
+            var items = Enumerable.Range(0, 3).Select(x => new ItemWithIsVisible(x)).ToList();
+            var (target, scroll, itemsControl) = CreateTarget(items: items, styles: new[] { style });
+            var container = target.ContainerFromIndex(2)!;
+
+            Assert.True(container.IsVisible);
+            Assert.Equal(20, container.Bounds.Top);
+
+            items[2].IsVisible = false;
+            Layout(target);
+
+            Assert.False(container.IsVisible);
+
+            items.RemoveAt(2);
+            items.Add(new ItemWithIsVisible(3));
+            Layout(target);
+
+            Assert.True(container.IsVisible);
+        }
+
         private static IReadOnlyList<int> GetRealizedIndexes(VirtualizingStackPanel target, ItemsControl itemsControl)
         {
             return target.GetRealizedElements()
@@ -1173,6 +1241,17 @@ namespace Avalonia.Controls.UnitTests
             return root;
         }
 
+        private static Style CreateIsVisibleBindingStyle()
+        {
+            return new Style(x => x.OfType<ContentPresenter>())
+            {
+                Setters =
+                {
+                    new Setter(Visual.IsVisibleProperty, new Binding("IsVisible")),
+                }
+            };
+        }
+
         private static IDataTemplate DefaultItemTemplate()
         {
             return new FuncDataTemplate<object>((x, _) => new Canvas { Width = 100, Height = 10 });
@@ -1218,6 +1297,24 @@ namespace Avalonia.Controls.UnitTests
             public double Height { get; set; }
         }
 
+        private class ItemWithIsVisible : NotifyingBase
+        {
+            private bool _isVisible = true;
+
+            public ItemWithIsVisible(int index)
+            {
+                Caption = $"Item {index}";
+            }
+
+            public string Caption { get; set; }
+
+            public bool IsVisible
+            {
+                get => _isVisible;
+                set => SetField(ref _isVisible, value);
+            }
+        }
+
         private class ResettingCollection : List<string>, INotifyCollectionChanged
         {
             public ResettingCollection(IEnumerable<string> items)