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* Add failing test for #20688 Unit test created from issue description * Add a failing test for wrong CacheLength handling All items would be realized which is obviously wrong * fix test setup used StackPanel instead of expcected VirtualizingStackPanel * Make sure the test actually fails * update comment * Fix for focusedElement and focusedIndex * add another unit test * Fixes for new test cases * Addressing Review * Update tests to match new behavior * only recycle focused element if it is not null * Address review * Address copilot reviewpull/20773/head
Tim
4 weeks ago
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GitHub
GitHub
3 changed files with 533 additions and 9 deletions
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using System.Collections.ObjectModel; |
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using System.Linq; |
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using Avalonia.Controls.Presenters; |
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using Avalonia.Controls.Primitives; |
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using Avalonia.Controls.Templates; |
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using Avalonia.Input; |
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using Avalonia.UnitTests; |
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using Xunit; |
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namespace Avalonia.Controls.UnitTests; |
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public class ListBoxVirtualizationIssueTests : ScopedTestBase |
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{ |
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[Fact] |
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public void Replaced_ItemsSource_Should_Not_Show_Old_Selected_Item_When_Scrolled_Back() |
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{ |
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using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface)) |
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{ |
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var letters = "ABCDEFGHIJ".Select(c => c.ToString()).ToList(); |
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var numbers = "0123456789".Select(c => c.ToString()).ToList(); |
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var target = new ListBox |
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{ |
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Template = new FuncControlTemplate(CreateListBoxTemplate), |
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ItemsSource = letters, |
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ItemTemplate = new FuncDataTemplate<string>((_, _) => new TextBlock { Height = 50 }), |
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Height = 100, // Show 2 items
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ItemsPanel = new FuncTemplate<Panel?>(() => new VirtualizingStackPanel { CacheLength = 0 }), |
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}; |
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Prepare(target); |
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// 1. Select a ListBoxItem
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target.SelectedIndex = 0; |
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Assert.True(((ListBoxItem)target.Presenter!.Panel!.Children[0]).IsSelected); |
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// 2. Scroll until the selected ListBoxItem is no longer visible
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target.ScrollIntoView(letters.Count - 1); // Scroll down to the last item
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// Verify that the first item is no longer realized
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var realizedContainers = target.GetRealizedContainers().Cast<ListBoxItem>().ToList(); |
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Assert.DoesNotContain(realizedContainers, x => x.Content as string == "A"); |
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// 3. Change the ItemsSource
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target.ItemsSource = numbers; |
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// 4. Scroll to the top
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target.ScrollIntoView(0); |
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// 5. The previously selected ListBoxItem should NOT appear in the ListBox
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var realizedItems = target.GetRealizedContainers() |
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.Cast<ListBoxItem>() |
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.Select(x => x.Content?.ToString()) |
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.ToList(); |
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Assert.All(realizedItems, item => Assert.DoesNotContain(item, letters)); |
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Assert.Equal("0", realizedItems[0]); |
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} |
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} |
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[Fact] |
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public void AddingItemsAtTopShouldNotCreateGhostItems() |
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{ |
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using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface)) |
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{ |
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ObservableCollection<Item> items = new(); |
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for (int i = 0; i < 100; i++) |
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{ |
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items.Add(new Item(i)); |
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} |
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var target = new ListBox |
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{ |
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Template = new FuncControlTemplate(CreateListBoxTemplate), |
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ItemsSource = items, |
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Height = 100, // Show 2 items
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ItemsPanel = new FuncTemplate<Panel?>(() => new VirtualizingStackPanel()), |
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}; |
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Prepare(target); |
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// Scroll to some position
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var scrollViewer = (ScrollViewer)target.VisualChildren[0]; |
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scrollViewer.Offset = new Vector(0, 500); // Scrolled down
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target.UpdateLayout(); |
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// Add items at the top multiple times
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for (int i = 0; i < 5; i++) |
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{ |
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for (int j = 0; j < 10; j++) |
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{ |
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items.Insert(0, new Item(1000 + (i * 100 + j))); |
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} |
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target.UpdateLayout(); |
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// Randomly select something
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target.SelectedIndex = items.Count - 1; |
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target.UpdateLayout(); |
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// Scroll a bit
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scrollViewer.ScrollToEnd(); |
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scrollViewer.ScrollToEnd(); |
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target.UpdateLayout(); |
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// Check for ghost items during the process
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var p = target.Presenter!.Panel!; |
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var visibleChildren = p.Children.Where(c => c.IsVisible).ToList(); |
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var realizedContainers = target.GetRealizedContainers() |
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.Cast<ListBoxItem>() |
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.ToList(); |
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// Only visible children should be considered. Invisible children may be recycled items kept for reuse.
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Assert.Equal(realizedContainers.Count, visibleChildren.Count); |
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foreach (var child in visibleChildren) |
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{ |
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Assert.Contains(child, realizedContainers); |
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} |
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var realizedItems = realizedContainers |
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.Select(x => x.Content) |
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.Cast<Item>() |
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.ToList(); |
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// Check for duplicates in realized items
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var duplicateIds = realizedItems.GroupBy(x => x.Id).Where(g => g.Count() > 1).Select(g => g.Key) |
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.ToList(); |
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Assert.Empty(duplicateIds); |
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// Check if all realized items are actually in the items source
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foreach (var item in realizedItems) |
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{ |
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Assert.Contains(item, items); |
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} |
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// Check if realized items are in the correct order
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int lastIndex = -1; |
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foreach (var item in realizedItems) |
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{ |
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int currentIndex = items.IndexOf(item); |
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Assert.True(currentIndex > lastIndex, |
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$"Item {item.Id} is at index {currentIndex}, but previous item was at index {lastIndex}"); |
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lastIndex = currentIndex; |
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} |
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// New check: verify that all visual children of the panel are accounted for in realizedContainers
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var panel = target.Presenter!.Panel!; |
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var visualChildren = panel.Children.ToList(); |
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// Realized containers should match exactly the visual children of the panel
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// (VirtualizingStackPanel manages its children such that they should be the realized containers)
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// We also check if all children are visible, if not they might be "ghosts"
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foreach (var child in visualChildren) |
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{ |
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Assert.True(child.IsVisible, $"Child {((ListBoxItem)child).Content} should be visible"); |
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} |
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Assert.Equal(realizedContainers.Count, visualChildren.Count); |
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foreach (var child in visualChildren) |
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{ |
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Assert.Contains(child, realizedContainers); |
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} |
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} |
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} |
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} |
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[Fact] |
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public void RealizedContainers_Should_Only_Include_Visible_Items_With_CacheLength_Zero() |
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{ |
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using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface)) |
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{ |
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var letters = "ABCDEFGHIJ".Select(c => c.ToString()).ToList(); |
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var target = new ListBox |
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{ |
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ItemsPanel = new FuncTemplate<Panel?>(() => new VirtualizingStackPanel { CacheLength = 0 }), |
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Template = new FuncControlTemplate(CreateListBoxTemplate), |
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ItemsSource = letters, |
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ItemTemplate = new FuncDataTemplate<string>((_, _) => new TextBlock { Height = 50 }), |
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Height = 100, // Show 2 items (100 / 50 = 2)
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}; |
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Prepare(target); |
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// At the top, only 2 items should be visible (items at index 0 and 1)
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var realizedContainers = target.GetRealizedContainers().Cast<ListBoxItem>().ToList(); |
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// With CacheLength = 0, we should only have the visible items realized
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Assert.Equal(2, realizedContainers.Count); |
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Assert.Equal("A", realizedContainers[0].Content?.ToString()); |
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Assert.Equal("B", realizedContainers[1].Content?.ToString()); |
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} |
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} |
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[Fact] |
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public void GhostItemTest_FocusManagement() |
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{ |
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using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface)) |
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{ |
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var items = new ObservableCollection<string>(Enumerable.Range(0, 100).Select(i => $"Item {i}")); |
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var target = new ListBox |
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{ |
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Template = new FuncControlTemplate(CreateListBoxTemplate), |
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ItemsSource = items, |
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ItemTemplate = new FuncDataTemplate<string>((_, _) => new TextBlock { Height = 50 }), |
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Height = 100, // Show 2 items
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ItemsPanel = new FuncTemplate<Panel?>(() => new VirtualizingStackPanel { CacheLength = 0 }), |
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}; |
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Prepare(target); |
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// 1. Get the first container and focus it
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var container = (ListBoxItem)target.Presenter!.Panel!.Children[0]; |
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KeyboardNavigation.SetTabOnceActiveElement(target, container); |
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// 2. Scroll down so the first item is recycled
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target.ScrollIntoView(10); |
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target.UpdateLayout(); |
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// 3. Verify it is now _focusedElement in the panel
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var panel = (VirtualizingStackPanel)target.Presenter!.Panel!; |
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var realizedContainers = target.GetRealizedContainers().ToList(); |
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// The focused container should still be in Children, but NOT in realizedContainers
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Assert.Contains(container, panel.Children); |
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Assert.DoesNotContain(container, realizedContainers); |
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// Now scroll back to top.
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target.ScrollIntoView(0); |
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target.UpdateLayout(); |
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// Check if we have two containers for the same item or other weirdness
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var visibleChildren = panel.Children.Where(c => c.IsVisible).ToList(); |
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// If it was a ghost, it might still be there or we might have two items for the same thing
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Assert.Equal(target.GetRealizedContainers().Count(), visibleChildren.Count); |
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// 4. Test: Re-insert at top might cause issues if _focusedElement is not updated correctly
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items.Insert(0, "New Item"); |
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target.UpdateLayout(); |
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visibleChildren = panel.Children.Where(c => c.IsVisible).ToList(); |
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Assert.Equal(target.GetRealizedContainers().Count(), visibleChildren.Count); |
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// 5. Remove the focused item while it's recycled
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target.ScrollIntoView(10); |
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target.UpdateLayout(); |
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Assert.Contains(container, panel.Children); |
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items.RemoveAt(1); // Item 0 was at index 1 because of Insert(0, "New Item")
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target.UpdateLayout(); |
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// container should be removed from children because RecycleElementOnItemRemoved is called
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Assert.DoesNotContain(container, panel.Children); |
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Assert.False(container.IsVisible); |
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} |
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} |
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[Fact] |
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public void GhostItemTest_ScrollToManagement() |
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{ |
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using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface)) |
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{ |
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var items = new ObservableCollection<string>(Enumerable.Range(0, 100).Select(i => $"Item {i}")); |
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var target = new ListBox |
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{ |
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Template = new FuncControlTemplate(CreateListBoxTemplate), |
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ItemsSource = items, |
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ItemTemplate = new FuncDataTemplate<string>((_, _) => new TextBlock { Height = 50 }), |
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Height = 100, // Show 2 items
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ItemsPanel = new FuncTemplate<Panel?>(() => new VirtualizingStackPanel { CacheLength = 0 }), |
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}; |
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Prepare(target); |
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// 1. ScrollIntoView to trigger _scrollToElement
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// We use a high index and don't call UpdateLayout immediately if we want to catch it in between?
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// Actually ScrollIntoView calls layout internally.
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target.ScrollIntoView(50); |
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var panel = (VirtualizingStackPanel)target.Presenter!.Panel!; |
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// 2. Remove the item we just scrolled to
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items.RemoveAt(50); |
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target.UpdateLayout(); |
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// If it was kept in _scrollToElement and not recycled, it might be a ghost.
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var visibleChildren = panel.Children.Where(c => c.IsVisible).ToList(); |
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Assert.Equal(target.GetRealizedContainers().Count(), visibleChildren.Count); |
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} |
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} |
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private Control CreateListBoxTemplate(TemplatedControl parent, INameScope scope) |
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{ |
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return new ScrollViewer |
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{ |
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Name = "PART_ScrollViewer", |
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Template = new FuncControlTemplate(CreateScrollViewerTemplate), |
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Content = new ItemsPresenter |
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{ |
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Name = "PART_ItemsPresenter", |
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[~ItemsPresenter.ItemsPanelProperty] = |
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((ListBox)parent).GetObservable(ItemsControl.ItemsPanelProperty).ToBinding(), |
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}.RegisterInNameScope(scope) |
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}.RegisterInNameScope(scope); |
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} |
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private Control CreateScrollViewerTemplate(TemplatedControl parent, INameScope scope) |
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{ |
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return new ScrollContentPresenter |
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{ |
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Name = "PART_ContentPresenter", |
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[~ContentPresenter.ContentProperty] = |
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parent.GetObservable(ContentControl.ContentProperty).ToBinding(), |
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}.RegisterInNameScope(scope); |
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} |
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private static void Prepare(ListBox target) |
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{ |
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target.Width = target.Height = 100; |
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var root = new TestRoot(target); |
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root.LayoutManager.ExecuteInitialLayoutPass(); |
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} |
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private class Item |
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{ |
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public Item(int id) |
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{ |
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Id = id; |
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} |
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public int Id { get; } |
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} |
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} |
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