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[release/10.0.1xx-sr2] [iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy (#33166)
Backport of #33161 to release/10.0.1xx-sr2 /cc @PureWeen @NanthiniMahalingam --------- Co-authored-by: NanthiniMahalingam <105482474+NanthiniMahalingam@users.noreply.github.com>
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‎src/Controls/src/Core/Handlers/Items2/iOS/GroupableItemsViewController2.cs‎

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@@ -127,6 +127,8 @@ void UpdateTemplatedSupplementaryView(TemplatedCell2 cell, NSString elementKind,
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var bindingContext = ItemsSource.Group(indexPath);
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// Mark this templated cell as a supplementary view (header/footer)
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cell.isSupplementaryView = true;
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cell.isHeaderOrFooterChanged = true;
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cell.Bind(template, bindingContext, ItemsView);
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cell.isHeaderOrFooterChanged = false;

‎src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs‎

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@@ -119,6 +119,8 @@ public override UICollectionViewCell GetCell(UICollectionView collectionView, NS
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{
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TemplatedCell2.ScrollDirection = ScrollDirection;
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// Ensure this cell is treated as a regular item cell (not a supplementary view)
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TemplatedCell2.isSupplementaryView = false;
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TemplatedCell2.Bind(ItemsView.ItemTemplate, ItemsSource[indexpathAdjusted], ItemsView);
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}
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else if (cell is DefaultCell2 DefaultCell2)

‎src/Controls/src/Core/Handlers/Items2/iOS/StructuredItemsViewController2.cs‎

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@@ -130,6 +130,7 @@ void UpdateTemplatedSupplementaryView(TemplatedCell2 cell, NSString elementKind)
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{
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bool isHeader = elementKind == UICollectionElementKindSectionKey.Header;
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cell.isHeaderOrFooterChanged = true;
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cell.isSupplementaryView = true;
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if (isHeader)
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{

‎src/Controls/src/Core/Handlers/Items2/iOS/TemplatedCell2.cs‎

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@@ -40,6 +40,8 @@ public event EventHandler<LayoutAttributesChangedEventArgs2> LayoutAttributesCha
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Size _measuredSize;
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Size _cachedConstraints;
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// Indicates the cell is being used as a supplementary view (group header/footer)
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internal bool isSupplementaryView = false;
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internal bool MeasureInvalidated => _measureInvalidated;
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// Flags changes confined to the header/footer, preventing unnecessary recycling and revalidation of templated cells.
@@ -107,20 +109,28 @@ public override UICollectionViewLayoutAttributes PreferredLayoutAttributesFittin
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if (_measureInvalidated || _cachedConstraints != constraints)
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{
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// Check if we should use the cached first item size for MeasureFirstItem optimization
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var cachedSize = GetCachedFirstItemSizeFromHandler();
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if (cachedSize != CGSize.Empty)
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// Only use the cached first-item measurement for actual item cells (not headers/footers)
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if (!isSupplementaryView)
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{
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_measuredSize = cachedSize.ToSize();
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// Even when we have a cached measurement, we still need to call Measure
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// to update the virtual view's internal state and bookkeeping
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virtualView.Measure(constraints.Width, _measuredSize.Height);
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var cachedSize = GetCachedFirstItemSizeFromHandler();
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if (cachedSize != CGSize.Empty)
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{
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_measuredSize = cachedSize.ToSize();
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// Even when we have a cached measurement, we still need to call Measure
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// to update the virtual view's internal state and bookkeeping
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virtualView.Measure(constraints.Width, _measuredSize.Height);
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}
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else
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{
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_measuredSize = virtualView.Measure(constraints.Width, constraints.Height);
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// If this is the first item being measured, cache it for MeasureFirstItem strategy
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SetCachedFirstItemSizeToHandler(_measuredSize.ToCGSize());
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}
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}
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else
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{
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// For headers/footers, always measure directly without using or updating the first-item cache
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_measuredSize = virtualView.Measure(constraints.Width, constraints.Height);
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// If this is the first item being measured, cache it for MeasureFirstItem strategy
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SetCachedFirstItemSizeToHandler(_measuredSize.ToCGSize());
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}
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_cachedConstraints = constraints;
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_needsArrange = true;
@@ -194,6 +204,7 @@ public override void LayoutSubviews()
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public override void PrepareForReuse()
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{
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//Unbind();
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isSupplementaryView = false;
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base.PrepareForReuse();
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}
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‎src/Controls/tests/TestCases.HostApp/Issues/Issue33130.xaml‎

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<?xml version="1.0" encoding="utf-8" ?>
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<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
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xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
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x:Class="Maui.Controls.Sample.Issues.Issue33130"
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xmlns:local="clr-namespace:Maui.Controls.Sample"
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Title="Issue33130">
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<Grid Margin="20"
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RowDefinitions="Auto, *">
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<StackLayout Grid.Row="0"
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Spacing="10"
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Margin="0,10">
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<Button Text="Switch to MeasureFirstItem"
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Clicked="OnSwitchToMeasureFirstItem"
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AutomationId="SwitchStrategyButton"/>
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<Label x:Name="StatusLabel"
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AutomationId="StatusLabel"
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Text="ItemSizingStrategy: MeasureAllItems"/>
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</StackLayout>
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<local:CollectionView2 Grid.Row="1"
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x:Name="TestCollectionView"
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ItemsSource="{Binding Animals}"
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IsGrouped="true"
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AutomationId="TestCollectionView"
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ItemSizingStrategy="MeasureAllItems">
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<local:CollectionView2.ItemTemplate>
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<DataTemplate>
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<Grid Padding="10">
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<Grid.RowDefinitions>
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<RowDefinition Height="Auto"/>
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<RowDefinition Height="Auto"/>
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</Grid.RowDefinitions>
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<Grid.ColumnDefinitions>
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<ColumnDefinition Width="Auto"/>
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<ColumnDefinition Width="*"/>
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</Grid.ColumnDefinitions>
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<Image Grid.RowSpan="2"
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Source="{Binding ImageUrl}"
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Aspect="AspectFill"
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WidthRequest="80"
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HeightRequest="80"/>
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<Label Grid.Column="1"
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Text="{Binding Name}"
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FontAttributes="Bold"/>
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<Label Grid.Row="1"
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Grid.Column="1"
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Text="{Binding Location}"
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FontAttributes="Italic"
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VerticalOptions="End"/>
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</Grid>
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</DataTemplate>
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</local:CollectionView2.ItemTemplate>
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<local:CollectionView2.GroupHeaderTemplate>
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<DataTemplate>
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<Label x:Name="GroupHeaderLabel"
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Text="{Binding Name}"
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BackgroundColor="LightGray"
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FontSize="20"
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FontAttributes="Bold"
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AutomationId="GroupHeader"/>
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</DataTemplate>
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</local:CollectionView2.GroupHeaderTemplate>
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<local:CollectionView2.GroupFooterTemplate>
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<DataTemplate>
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<Label Text="{Binding Count, StringFormat='Total animals: {0:D}'}"
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Margin="0,0,0,10"/>
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</DataTemplate>
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</local:CollectionView2.GroupFooterTemplate>
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</local:CollectionView2>
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</Grid>
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</ContentPage>

‎src/Controls/tests/TestCases.HostApp/Issues/Issue33130.xaml.cs‎

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using System;
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using System.Collections.ObjectModel;
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using Microsoft.Maui.Controls;
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namespace Maui.Controls.Sample.Issues;
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[Issue(IssueTracker.Github, 33130, "CollectionView group header size changes with ItemSizingStrategy", PlatformAffected.iOS | PlatformAffected.macOS)]
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public partial class Issue33130 : ContentPage
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{
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public Issue33130()
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{
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InitializeComponent();
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BindingContext = new GroupedAnimalsViewModel();
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}
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private void OnSwitchToMeasureFirstItem(object sender, EventArgs e)
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{
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TestCollectionView.ItemSizingStrategy = ItemSizingStrategy.MeasureFirstItem;
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StatusLabel.Text = $"ItemSizingStrategy: {TestCollectionView.ItemSizingStrategy}";
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}
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}
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public class GroupedAnimalsViewModel
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{
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public ObservableCollection<GroupHeaderTestAnimalGroup> Animals { get; set; }
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public GroupedAnimalsViewModel()
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{
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Animals = new ObservableCollection<GroupHeaderTestAnimalGroup>
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{
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new GroupHeaderTestAnimalGroup("Bears")
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{
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new GroupHeaderTestAnimal { Name = "Grizzly Bear", Location = "North America", ImageUrl = "bear.jpg" },
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new GroupHeaderTestAnimal { Name = "Polar Bear", Location = "Arctic", ImageUrl = "bear.jpg" },
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},
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new GroupHeaderTestAnimalGroup("Monkeys")
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{
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new GroupHeaderTestAnimal { Name = "Baboon", Location = "Africa", ImageUrl = "monkey.jpg" },
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new GroupHeaderTestAnimal { Name = "Capuchin Monkey", Location = "South America", ImageUrl = "monkey.jpg" },
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new GroupHeaderTestAnimal { Name = "Spider Monkey", Location = "Central America", ImageUrl = "monkey.jpg" },
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},
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new GroupHeaderTestAnimalGroup("Elephants")
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{
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new GroupHeaderTestAnimal { Name = "African Elephant", Location = "Africa", ImageUrl = "elephant.jpg" },
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new GroupHeaderTestAnimal { Name = "Asian Elephant", Location = "Asia", ImageUrl = "elephant.jpg" },
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}
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};
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}
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}
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public class GroupHeaderTestAnimalGroup : ObservableCollection<GroupHeaderTestAnimal>
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{
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public string Name { get; set; }
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public GroupHeaderTestAnimalGroup(string name) : base()
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{
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Name = name;
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}
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}
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public class GroupHeaderTestAnimal
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{
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public string Name { get; set; }
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public string Location { get; set; }
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public string ImageUrl { get; set; }
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}

‎src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33130.cs‎

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using NUnit.Framework;
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using UITest.Appium;
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using UITest.Core;
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namespace Microsoft.Maui.TestCases.Tests.Issues;
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public class Issue33130 : _IssuesUITest
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{
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public override string Issue => "CollectionView group header size changes with ItemSizingStrategy";
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public Issue33130(TestDevice device) : base(device) { }
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[Test]
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[Category(UITestCategories.CollectionView)]
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public void GroupHeaderSizeShouldNotChangeWithItemSizingStrategy()
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{
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// Wait for the CollectionView to load
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App.WaitForElement("TestCollectionView");
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App.WaitForElement("GroupHeader");
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// Get the initial header size (before changing ItemSizingStrategy)
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var headerElementBefore = App.FindElement("GroupHeader");
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var headerRectBefore = headerElementBefore.GetRect();
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Assert.That(headerRectBefore.Height, Is.GreaterThan(0), "Header should have a height before strategy change");
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// Switch ItemSizingStrategy
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App.WaitForElement("SwitchStrategyButton");
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App.Tap("SwitchStrategyButton");
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// Get the header size after changing ItemSizingStrategy
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var headerElementAfter = App.FindElement("GroupHeader");
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var headerRectAfter = headerElementAfter.GetRect();
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Assert.That(headerRectAfter.Height, Is.GreaterThan(0), "Header should have a height after strategy change");
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// The header size should remain the same (within a small tolerance for rendering differences)
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// Allow for small rounding differences but not significant changes
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var heightDifference = Math.Abs(headerRectBefore.Height - headerRectAfter.Height);
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// Assert that the height difference is minimal (less than 5 pixels tolerance)
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Assert.That(heightDifference, Is.EqualTo(0),
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$"Header height should not change significantly. Before: {headerRectBefore.Height}, After: {headerRectAfter.Height}, Difference: {heightDifference}");
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}
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}

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