CollectionView2 Items display issue when Header is resized on iOS

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

@@ -14,6 +14,11 @@ public class StructuredItemsViewController2<TItemsView> : ItemsViewController2<T
 		public const int HeaderTag = 111;
 		public const int FooterTag = 222;
 
+		View _headerView;
+		View _footerView;
+		EventHandler _footerMeasureInvalidated;
+		EventHandler _headerMeasureInvalidated;
+
 		bool _disposed;
 
 		public StructuredItemsViewController2(TItemsView structuredItemsView, UICollectionViewLayout layout)
@@ -40,7 +45,11 @@ protected override void Dispose(bool disposing)
 
 			if (disposing)
 			{
+				if (_headerView != null)
+					_headerView.MeasureInvalidated -= _headerMeasureInvalidated;
 
+				if (_footerView != null)
+					_footerView.MeasureInvalidated -= _footerMeasureInvalidated;
 			}
 
 			base.Dispose(disposing);
@@ -115,26 +124,54 @@ void UpdateTemplatedSupplementaryView(TemplatedCell2 cell, NSString elementKind)
 
 			if (isHeader)
 			{
+				if (_headerView != null)
+					_headerView.MeasureInvalidated -= _headerMeasureInvalidated;
+
 				if (ItemsView.Header is View headerView)
 				{
+					_headerView = headerView;
 					cell.Bind(headerView, ItemsView);
 				}
 				else if (ItemsView.HeaderTemplate is not null)
 				{
+					_headerView = (View)ItemsView.HeaderTemplate.CreateContent();
 					cell.Bind(ItemsView.HeaderTemplate, ItemsView.Header, ItemsView);
 				}
+
+				_headerMeasureInvalidated = (s, e) =>
+				{
+					var indexPath = CollectionView.GetIndexPathForSupplementaryView(cell);
+					if (indexPath != null)
+						CollectionView.ReloadItems([indexPath]);
+				};
+
+				_headerView.MeasureInvalidated += _headerMeasureInvalidated;
 				cell.Tag = HeaderTag;
 			}
 			else
 			{
+				if (_footerView != null)
+					_footerView.MeasureInvalidated -= _footerMeasureInvalidated;
+
 				if (ItemsView.Footer is View footerView)
 				{
+					_footerView = footerView;
 					cell.Bind(footerView, ItemsView);
 				}
 				else if (ItemsView.FooterTemplate is not null)
 				{
+					_footerView = (View)ItemsView.FooterTemplate.CreateContent();
 					cell.Bind(ItemsView.FooterTemplate, ItemsView.Footer, ItemsView);
 				}
+
+				_footerMeasureInvalidated = (s, e) =>
+				{
+					var indexPath = CollectionView.GetIndexPathForSupplementaryView(cell);
+					if (indexPath != null)
+						CollectionView.ReloadItems([indexPath]);
+				};
+
+				_footerView.MeasureInvalidated += _footerMeasureInvalidated;
 				cell.Tag = FooterTag;
 			}
 		}

src/Controls/tests/TestCases.HostApp/Issues/Issue25362.xaml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue25362"
+             x:Name="Self"
+             Title="Issue25362">
+    <Grid RowDefinitions="Auto,*">
+        <HorizontalStackLayout Grid.Row="0">
+            <Button
+                Command="{Binding AddCommand}"
+                HorizontalOptions="Center"
+                AutomationId="button"
+                Text="Add" />
+        </HorizontalStackLayout>
+
+        <CollectionView
+            Grid.Row="1"
+            ItemsSource="{Binding ItemList}">
+
+            <CollectionView.Header>
+                <VerticalStackLayout>
+                    <VerticalStackLayout BindableLayout.ItemsSource="{Binding BindingContext.ItemListHeader, Source={x:Reference Self}}">
+                        <BindableLayout.ItemTemplate>
+                            <DataTemplate>
+                                <Label Padding="10" Text="{Binding .}" />
+                            </DataTemplate>
+                        </BindableLayout.ItemTemplate>
+                    </VerticalStackLayout>
+                    <BoxView
+                        Margin="0,5"
+                        HeightRequest="2"
+                        Color="Black" />
+                </VerticalStackLayout>
+            </CollectionView.Header>
+
+            <CollectionView.ItemTemplate>
+                <DataTemplate>
+                    <Label Padding="10" Text="{Binding .}" />
+                </DataTemplate>
+            </CollectionView.ItemTemplate>
+        </CollectionView>
+    </Grid>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue25362.xaml.cs

@@ -0,0 +1,21 @@
+using System.Collections.ObjectModel;
+namespace Maui.Controls.Sample.Issues;
+
+[XamlCompilation(XamlCompilationOptions.Compile)]
+[Issue(IssueTracker.Github, 25362, "[iOS] CollectionView Items display issue when Header is resized", PlatformAffected.iOS)]
+
+public partial class Issue25362 : ContentPage
+{
+	public ObservableCollection<string> ItemList { get; }
+	public ObservableCollection<string> ItemListHeader { get; }
+
+	public Command AddCommand => new(() => ItemListHeader.Add($"HeaderItem{ItemListHeader.Count + 1}"));
+
+	public Issue25362()
+	{
+		InitializeComponent();
+		ItemList = new() { "Item1", "Item2", "Itme3" };
+		ItemListHeader = new() { "HeaderItem1" };
+		BindingContext = this;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue25362.cs

@@ -0,0 +1,26 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue25362 : _IssuesUITest
+{
+	public override string Issue => "[iOS] CollectionView Items display issue when Header is resized";
+
+	public Issue25362(TestDevice device) : base(device)
+	{ }
+
+	[Test]
+	[Category(UITestCategories.CollectionView)]
+	public void HeaderShouldNotCollapseWithItems()
+	{
+		App.WaitForElement("button");
+		App.Click("button");
+		App.Click("button");
+		App.Click("button");
+
+		//The test passes of header has 4 elements that don't overlap with the collection view's items
+		VerifyScreenshot();
+	}
+}