Fix header/footer cropping in CollectionView with horizontal grid layout on iOS/Mac

src/Controls/src/Core/Handlers/Items/iOS/StructuredItemsViewController.cs

@@ -156,7 +156,9 @@ void UpdateHeaderFooterPosition()
 
 				if (_headerUIView != null && _headerUIView.Frame.X != -headerWidth)
 				{
-					_headerUIView.Frame = new CGRect(-headerWidth, 0, headerWidth, CollectionView.Frame.Height);
+					// Use the actual measured height of the header view instead of the full CollectionView height
+					nfloat headerHeight = _headerUIView.Frame.Height;
+					_headerUIView.Frame = new CGRect(-headerWidth, 0, headerWidth, headerHeight);
 				}
 
 				if (_footerUIView != null && IsViewLoaded && View.Window != null)
@@ -167,7 +169,9 @@ void UpdateHeaderFooterPosition()
 
 					if (currentFrame.X != footerX)
 					{
-						_footerUIView.Frame = new CGRect(footerX, 0, footerWidth, CollectionView.Frame.Height);
+						// Use the actual measured height of the footer view instead of the full CollectionView height
+						nfloat footerHeight = _footerUIView.Frame.Height;
+						_footerUIView.Frame = new CGRect(footerX, 0, footerWidth, footerHeight);
 					}
 				}
 			}

src/Controls/src/Core/Handlers/Items2/iOS/LayoutFactory2.cs

@@ -25,14 +25,19 @@ public static UICollectionViewLayout CreateGrid(GridItemsLayout gridItemsLayout,
 	static NSCollectionLayoutBoundarySupplementaryItem[] CreateSupplementaryItems(LayoutGroupingInfo? groupingInfo, LayoutHeaderFooterInfo? layoutHeaderFooterInfo,
 		UICollectionViewScrollDirection scrollDirection, NSCollectionLayoutDimension width, NSCollectionLayoutDimension height)
 	{
+		// For horizontal layouts, use estimated dimensions for headers/footers instead of full group height
+		// This prevents headers/footers from being cropped when group height is fractional (full height)
+		var headerFooterWidth = scrollDirection == UICollectionViewScrollDirection.Horizontal ? NSCollectionLayoutDimension.CreateEstimated(30f) : width;
+		var headerFooterHeight = scrollDirection == UICollectionViewScrollDirection.Horizontal ? NSCollectionLayoutDimension.CreateEstimated(30f) : height;
+
 		if (groupingInfo is not null && groupingInfo.IsGrouped)
 		{
 			var items = new List<NSCollectionLayoutBoundarySupplementaryItem>();
 
 			if (groupingInfo.HasHeader)
 			{
 				items.Add(NSCollectionLayoutBoundarySupplementaryItem.Create(
-					NSCollectionLayoutSize.Create(width, height),
+					NSCollectionLayoutSize.Create(headerFooterWidth, headerFooterHeight),
 					UICollectionElementKindSectionKey.Header.ToString(),
 					scrollDirection == UICollectionViewScrollDirection.Vertical
 						? NSRectAlignment.Top
@@ -42,7 +47,7 @@ static NSCollectionLayoutBoundarySupplementaryItem[] CreateSupplementaryItems(La
 			if (groupingInfo.HasFooter)
 			{
 				items.Add(NSCollectionLayoutBoundarySupplementaryItem.Create(
-					NSCollectionLayoutSize.Create(width, height),
+					NSCollectionLayoutSize.Create(headerFooterWidth, headerFooterHeight),
 					UICollectionElementKindSectionKey.Footer.ToString(),
 					scrollDirection == UICollectionViewScrollDirection.Vertical
 						? NSRectAlignment.Bottom
@@ -59,7 +64,7 @@ static NSCollectionLayoutBoundarySupplementaryItem[] CreateSupplementaryItems(La
 			if (layoutHeaderFooterInfo.HasHeader)
 			{
 				items.Add(NSCollectionLayoutBoundarySupplementaryItem.Create(
-					NSCollectionLayoutSize.Create(width, height),
+					NSCollectionLayoutSize.Create(headerFooterWidth, headerFooterHeight),
 					UICollectionElementKindSectionKey.Header.ToString(),
 					scrollDirection == UICollectionViewScrollDirection.Vertical
 						? NSRectAlignment.Top
@@ -70,7 +75,7 @@ static NSCollectionLayoutBoundarySupplementaryItem[] CreateSupplementaryItems(La
 			if (layoutHeaderFooterInfo.HasFooter)
 			{
 				items.Add(NSCollectionLayoutBoundarySupplementaryItem.Create(
-					NSCollectionLayoutSize.Create(width, height),
+					NSCollectionLayoutSize.Create(headerFooterWidth, headerFooterHeight),
 					UICollectionElementKindSectionKey.Footer.ToString(),
 					scrollDirection == UICollectionViewScrollDirection.Vertical
 						? NSRectAlignment.Bottom

src/Controls/tests/TestCases.HostApp/Issues/Issue26835.xaml

@@ -0,0 +1,80 @@
+<?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.Issue26835"
+             Title="Issue 26835">
+    <Grid>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto" />
+            <RowDefinition Height="*" />
+        </Grid.RowDefinitions>
+
+        <Label Grid.Row="0" 
+               Text="Horizontal Grid CollectionView with Header/Footer - Should show full header and footer without cropping" 
+               FontSize="16" 
+               Margin="10" />
+
+        <CollectionView Grid.Row="1" 
+                        x:Name="CollectionView"
+                        AutomationId="HorizontalGridCollectionView"
+                        BackgroundColor="LightGray">
+
+            <CollectionView.ItemsLayout>
+                <GridItemsLayout Span="3" 
+                                 Orientation="Horizontal" 
+                                 HorizontalItemSpacing="5" 
+                                 VerticalItemSpacing="5" />
+            </CollectionView.ItemsLayout>
+
+            <CollectionView.Header>
+                <StackLayout BackgroundColor="Blue" Padding="10" AutomationId="CollectionViewHeader">
+                    <Label Text="HEADER CONTENT" 
+                           TextColor="White" 
+                           FontSize="18" 
+                           FontAttributes="Bold"
+                           HorizontalOptions="Center" 
+                           AutomationId="HeaderTitle" />
+                    <Label Text="This header should be fully visible" 
+                           TextColor="White" 
+                           HorizontalOptions="Center" 
+                           AutomationId="HeaderSubtitle" />
+                    <Label Text="Line 3 of header content" 
+                           TextColor="White" 
+                           HorizontalOptions="Center" 
+                           AutomationId="HeaderLine3" />
+                </StackLayout>
+            </CollectionView.Header>
+
+            <CollectionView.Footer>
+                <StackLayout BackgroundColor="Red" Padding="10" AutomationId="CollectionViewFooter">
+                    <Label Text="FOOTER CONTENT" 
+                           TextColor="White" 
+                           FontSize="18" 
+                           FontAttributes="Bold"
+                           HorizontalOptions="Center" 
+                           AutomationId="FooterTitle" />
+                    <Label Text="This footer should be fully visible" 
+                           TextColor="White" 
+                           HorizontalOptions="Center" 
+                           AutomationId="FooterSubtitle" />
+                    <Label Text="Line 3 of footer content" 
+                           TextColor="White" 
+                           HorizontalOptions="Center" 
+                           AutomationId="FooterLine3" />
+                </StackLayout>
+            </CollectionView.Footer>
+
+            <CollectionView.ItemTemplate>
+                <DataTemplate>
+                    <Grid BackgroundColor="LightBlue" HeightRequest="80" WidthRequest="80">
+                        <Label Text="{Binding .}" 
+                               HorizontalOptions="Center" 
+                               VerticalOptions="Center" 
+                               FontSize="14" />
+                    </Grid>
+                </DataTemplate>
+            </CollectionView.ItemTemplate>
+
+        </CollectionView>
+    </Grid>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue26835.xaml.cs

@@ -0,0 +1,29 @@
+using System.Collections.ObjectModel;
+using Microsoft.Maui.Controls;
+
+namespace Maui.Controls.Sample.Issues
+{
+    [Issue(IssueTracker.Github, 26835, "[iOS & Mac] Headers and Footers Get Cropped in CollectionView with Horizontal Grid and Horizontal Orientation",
+        PlatformAffected.iOS | PlatformAffected.macOS)]
+    public partial class Issue26835 : ContentPage
+    {
+        public ObservableCollection<string> Items { get; set; }
+
+        public Issue26835()
+        {
+            InitializeComponent();
+
+            // Create test data with enough items to demonstrate horizontal scrolling
+            Items = new ObservableCollection<string>();
+            for (int i = 1; i <= 30; i++)
+            {
+                Items.Add($"Item {i}");
+            }
+
+            CollectionView.ItemsSource = Items;
+
+            // Additional verification: Set AutomationIds for testing
+            CollectionView.AutomationId = "HorizontalGridCollectionView";
+        }
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue26835.cs

@@ -0,0 +1,48 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+    public class Issue26835 : _IssuesUITest
+    {
+        public Issue26835(TestDevice device) : base(device) { }
+
+        public override string Issue => "[iOS & Mac] Headers and Footers Get Cropped in CollectionView with Horizontal Grid and Horizontal Orientation";
+
+        [Test]
+        [Category(UITestCategories.CollectionView)]
+        public void HeaderAndFooterShouldNotBeCroppedInHorizontalGrid()
+        {
+            // Verify the CollectionView is present
+            App.WaitForElement("HorizontalGridCollectionView");
+
+            // Verify header elements are visible and not cropped
+            App.WaitForElement("HeaderTitle");
+            App.WaitForElement("HeaderSubtitle");  
+            App.WaitForElement("HeaderLine3");
+
+            // Scroll to the right to reveal the footer at the end of the collection
+            for (int i = 0; i < 8; i++)
+            {
+                App.ScrollRight("HorizontalGridCollectionView", ScrollStrategy.Auto, 0.8, 500);
+            }
+
+            // Verify footer elements are visible and not cropped
+            App.WaitForElement("FooterTitle");
+            App.WaitForElement("FooterSubtitle");
+            App.WaitForElement("FooterLine3");
+
+            // Scroll back to verify header is still visible
+            for (int i = 0; i < 8; i++)
+            {
+                App.ScrollLeft("HorizontalGridCollectionView", ScrollStrategy.Auto, 0.8, 500);
+            }
+
+            // Verify header is still visible after scrolling
+            App.WaitForElement("HeaderTitle");
+            App.WaitForElement("HeaderSubtitle");
+            App.WaitForElement("HeaderLine3");
+        }
+    }
+}