Use ItemTemplate for ComboBox's selection box for controls (#21937)

* Add failing tests for SelectionBoxItem with a control * Use ItemTemplate for ComboBox's selection box for controls * Add failing selection box tests when properties change * Update selection box when its template changes
3 weeks ago · a13617dfdf
3 changed files with 239 additions and 24 deletions
--- a/src/Avalonia.Controls/ComboBox.cs
+++ b/src/Avalonia.Controls/ComboBox.cs
@ -102,7 +102,7 @@ namespace Avalonia.Controls
            if (template is not null) return template;
            if(obj is ComboBox comboBox && template is null)
            {
-                return comboBox.ItemTemplate;
+                return comboBox.GetEffectiveItemTemplate();
            }
            return template;
        }
@ -425,6 +425,10 @@ namespace Avalonia.Controls
            {
                CoerceValue(SelectionBoxItemTemplateProperty);
            }
+            else if (change.Property == SelectionBoxItemTemplateProperty)
+            {
+                UpdateSelectionBoxItem(SelectedItem);
+            }
            else if (change.Property == IsEditableProperty && change.GetNewValue<bool>())
            {
                UpdateInputTextFromSelection(SelectedItem);
@ -444,6 +448,10 @@ namespace Avalonia.Controls
            else if (change.Property == DisplayMemberBindingProperty)
            {
                HandleTextValueBindingValueChanged(null, change);
+                // The base handler invalidates the cached template: run it before coercing.
+                base.OnPropertyChanged(change);
+                CoerceValue(SelectionBoxItemTemplateProperty);
+                return;
            }
            else if (change.Property == TextSearch.TextBindingProperty)
            {
@ -533,18 +541,24 @@ namespace Avalonia.Controls

        private void UpdateSelectionBoxItem(object? item)
        {
-            var contentControl = item as IContentControl;
-
-            if (contentControl != null)
+            if (item is IContentControl contentControl)
            {
                item = contentControl.Content;
            }

-            var control = item as Control;
+            if (item is null)
+            {
+                SelectionBoxItem = null;
+                return;
+            }

-            if (control != null)
+            if (SelectionBoxItemTemplate is not null)
            {
-                if (VisualRoot is object)
+                SelectionBoxItem = item;
+            }
+            else if (item is Control control)
+            {
+                if (VisualRoot is not null)
                {
                    control.Measure(Size.Infinity);

@ -565,22 +579,7 @@ namespace Avalonia.Controls
            }
            else
            {
-                if (item is not null && ItemTemplate is null && SelectionBoxItemTemplate is null && DisplayMemberBinding is { } binding)
-                {
-                    var template = new FuncDataTemplate<object?>((_, _) =>
-                    new TextBlock
-                    {
-                        [TextBlock.DataContextProperty] = item,
-                        [!TextBlock.TextProperty] = binding,
-                    });
-                    var text = template.Build(item);
-                    SelectionBoxItem = text;
-                }
-                else
-                {
-                    SelectionBoxItem = item;
-                }
-                
+                SelectionBoxItem = item;
            }
        }

--- a/src/Avalonia.Controls/ItemsControl.cs
+++ b/src/Avalonia.Controls/ItemsControl.cs
@ -776,7 +776,7 @@ namespace Avalonia.Controls
                LogicalChildren.RemoveAll(toRemove);
        }

-        private IDataTemplate? GetEffectiveItemTemplate()
+        private protected IDataTemplate? GetEffectiveItemTemplate()
        {
            if (ItemTemplate is { } itemTemplate)
                return itemTemplate;
--- a/tests/Avalonia.Controls.UnitTests/ComboBoxTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ComboBoxTests.cs
@ -702,6 +702,222 @@ namespace Avalonia.Controls.UnitTests
            Assert.Null(target.SelectionBoxItem);
        }

+        [Fact]
+        public void ItemTemplate_Is_Applied_To_Control_Item_In_DropDown()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas();
+            var target = new ComboBox
+            {
+                Items = { item },
+                ItemTemplate = new FuncDataTemplate<object?>((x, _) => new TextBlock { Tag = x }),
+                SelectedIndex = 0
+            };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            target.IsDropDownOpen = true;
+            window.LayoutManager.ExecuteLayoutPass();
+
+            var container = Assert.IsType<ComboBoxItem>(target.ContainerFromIndex(0));
+            var textBlock = Assert.IsType<TextBlock>(container.Presenter?.Child);
+            Assert.Same(item, textBlock.Tag);
+        }
+
+        [Fact]
+        public void DisplayMemberBinding_Is_Applied_To_Control_Item_In_DropDown()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas { Tag = "foo" };
+            var target = new ComboBox
+            {
+                Items = { item },
+                DisplayMemberBinding = CompiledBinding.Create((Canvas c) => c.Tag),
+                SelectedIndex = 0
+            };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            target.IsDropDownOpen = true;
+            window.LayoutManager.ExecuteLayoutPass();
+
+            var container = Assert.IsType<ComboBoxItem>(target.ContainerFromIndex(0));
+            var textBlock = Assert.IsType<TextBlock>(container.Presenter?.Child);
+            Assert.Equal("foo", textBlock.Text);
+        }
+
+        [Fact]
+        public void ItemTemplate_Is_Applied_To_Control_Item_In_SelectionBox()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas();
+            var target = new ComboBox
+            {
+                Items = { item },
+                ItemTemplate = new FuncDataTemplate<object?>((x, _) => new TextBlock { Tag = x }),
+                SelectedIndex = 0
+            };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            var selectionBoxControl = target.FindDescendantOfType<ContentControl>(
+                false, c => c.ContentTemplate == target.SelectionBoxItemTemplate);
+            Assert.NotNull(selectionBoxControl);
+            var textBlock = Assert.IsType<TextBlock>(selectionBoxControl.Presenter?.Child);
+            Assert.Same(item, textBlock.Tag);
+        }
+
+        [Fact]
+        public void DisplayMemberBinding_Is_Applied_To_Control_Item_In_SelectionBox()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas { Tag = "foo" };
+
+            var target = new ComboBox
+            {
+                Items = { item },
+                DisplayMemberBinding = CompiledBinding.Create((Canvas c) => c.Tag),
+                SelectedIndex = 0
+            };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            var selectionBoxControl = target.FindDescendantOfType<ContentControl>(
+                false, c => c.ContentTemplate == target.SelectionBoxItemTemplate);
+            Assert.NotNull(selectionBoxControl);
+            var textBlock = Assert.IsType<TextBlock>(selectionBoxControl.Presenter?.Child);
+            Assert.Equal("foo", textBlock.Text);
+        }
+
+        [Fact]
+        public void SelectionBoxItemTemplate_Is_Applied_To_Control_Item_In_SelectionBox()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas();
+            var target = new ComboBox
+            {
+                Items = { item },
+                SelectionBoxItemTemplate = new FuncDataTemplate<object?>((x, _) => new TextBlock { Tag = x }),
+                SelectedIndex = 0
+            };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            var selectionBoxControl = target.FindDescendantOfType<ContentControl>(
+                false, c => c.ContentTemplate == target.SelectionBoxItemTemplate);
+            Assert.NotNull(selectionBoxControl);
+            var textBlock = Assert.IsType<TextBlock>(selectionBoxControl.Presenter?.Child);
+            Assert.Same(item, textBlock.Tag);
+        }
+
+        [Fact]
+        public void ItemTemplate_Is_Applied_To_Control_Item_In_SelectionBox_When_Changed()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas();
+            var target = new ComboBox { Items = { item }, SelectedIndex = 0 };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            AssertSelectionBoxItemIsVisualBrushOf(target, item);
+
+            target.ItemTemplate = new FuncDataTemplate<object?>((x, _) => new TextBlock { Tag = x });
+            window.LayoutManager.ExecuteLayoutPass();
+
+            var textBlock = Assert.IsType<TextBlock>(GetSelectionBoxControl(target).Presenter?.Child);
+            Assert.Same(item, textBlock.Tag);
+
+            target.ItemTemplate = null;
+            window.LayoutManager.ExecuteLayoutPass();
+
+            AssertSelectionBoxItemIsVisualBrushOf(target, item);
+        }
+
+        [Fact]
+        public void DisplayMemberBinding_Is_Applied_To_Control_Item_In_SelectionBox_When_Changed()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas { Tag = "foo" };
+            var target = new ComboBox { Items = { item }, SelectedIndex = 0 };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            AssertSelectionBoxItemIsVisualBrushOf(target, item);
+
+            target.DisplayMemberBinding = CompiledBinding.Create((Canvas c) => c.Tag);
+            window.LayoutManager.ExecuteLayoutPass();
+
+            var textBlock = Assert.IsType<TextBlock>(GetSelectionBoxControl(target).Presenter?.Child);
+            Assert.Equal("foo", textBlock.Text);
+
+            target.DisplayMemberBinding = null;
+            window.LayoutManager.ExecuteLayoutPass();
+
+            AssertSelectionBoxItemIsVisualBrushOf(target, item);
+        }
+
+        [Fact]
+        public void SelectionBoxItemTemplate_Is_Applied_To_Control_Item_In_SelectionBox_When_Changed()
+        {
+            using var app = UnitTestApplication.Start(TestServices.StyledWindow);
+
+            var item = new Canvas();
+            var target = new ComboBox { Items = { item }, SelectedIndex = 0 };
+
+            var window = new Window { Content = target };
+            window.Show();
+            window.LayoutManager.ExecuteInitialLayoutPass();
+
+            AssertSelectionBoxItemIsVisualBrushOf(target, item);
+
+            target.SelectionBoxItemTemplate = new FuncDataTemplate<object?>((x, _) => new TextBlock { Tag = x });
+            window.LayoutManager.ExecuteLayoutPass();
+
+            var textBlock = Assert.IsType<TextBlock>(GetSelectionBoxControl(target).Presenter?.Child);
+            Assert.Same(item, textBlock.Tag);
+
+            target.SelectionBoxItemTemplate = null;
+            window.LayoutManager.ExecuteLayoutPass();
+
+            AssertSelectionBoxItemIsVisualBrushOf(target, item);
+        }
+
+        private static ContentControl GetSelectionBoxControl(ComboBox target)
+        {
+            var selectionBoxControl = target.FindDescendantOfType<ContentControl>(
+                false, c => c.ContentTemplate == target.SelectionBoxItemTemplate);
+            Assert.NotNull(selectionBoxControl);
+            return selectionBoxControl;
+        }
+
+        private static void AssertSelectionBoxItemIsVisualBrushOf(ComboBox target, Control item)
+        {
+            var rectangle = Assert.IsType<Rectangle>(target.SelectionBoxItem);
+            var visualBrush = Assert.IsType<VisualBrush>(rectangle.Fill);
+            Assert.Same(item, visualBrush.Visual);
+        }
+
        private sealed record Item(string Value, string Display);

        [Fact]