[iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy #33161

NanthiniMahalingam · 2025-12-15T13:20:55Z

Root cause

When the ItemSizingStrategy is set to measure the first item, the collection view’s grouped item header or footer template size is taken from the first item’s size instead of the actual size of the grouped item header or footer template.

Description of changes

I have ignored the first measured item’s size when applying it to the grouped header or footer template, the collection view header or footer view, and the collection view header or footer template in PreferredLayoutAttributesFittingAttributes of TemplatedCell2.

Issues Fixed

Fixes #33130

Validated the behaviour in the following platforms

Android
Windows ,
iOS,
MacOS

Output

iOS

Before	After
issue33130_iOS_before.mov	Issue33130_iOS_after.mov

macOS

Before	After
issue33130_mac_before.mov	Issue33130_mac_after.mov

Copilot

Pull request overview

This PR fixes a CollectionView issue on iOS and macOS where group headers and footers incorrectly inherit the size of the first measured item when the ItemSizingStrategy is set to MeasureFirstItem. The fix introduces a boolean flag isSupplementaryView to distinguish supplementary views (headers/footers) from regular item cells, ensuring headers/footers are always measured directly and never use the cached first-item measurement.

Key Changes:

Added flag to prevent headers/footers from using the first-item measurement cache
Updated measurement logic to conditionally apply cached measurements only to item cells
Added comprehensive UI test to verify the fix works correctly

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
`src/Controls/src/Core/Handlers/Items2/iOS/TemplatedCell2.cs`	Adds `isSupplementaryView` flag and updates measurement logic to skip cached measurements for headers/footers
`src/Controls/src/Core/Handlers/Items2/iOS/StructuredItemsViewController2.cs`	Sets the `isSupplementaryView` flag when configuring supplementary views
`src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs`	Explicitly clears the `isSupplementaryView` flag for regular item cells
`src/Controls/src/Core/Handlers/Items2/iOS/GroupableItemsViewController2.cs`	Sets the `isSupplementaryView` flag for group headers and footers
`src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33130.cs`	NUnit test that verifies header height remains constant when ItemSizingStrategy changes
`src/Controls/tests/TestCases.HostApp/Issues/Issue33130.xaml`	XAML test page with grouped CollectionView and button to switch sizing strategy
`src/Controls/tests/TestCases.HostApp/Issues/Issue33130.xaml.cs`	Code-behind with view models demonstrating the group header sizing issue

Copilot · 2025-12-15T15:14:42Z

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

 		Size _cachedConstraints;

+		// Indicates the cell is being used as a supplementary view (group header/footer)
+		internal bool isSupplementaryView = false;


The field isSupplementaryView does not follow C# naming conventions. Internal fields should use PascalCase with an underscore prefix (e.g., _isSupplementaryView) to be consistent with other fields in this class like _measureInvalidated, _needsArrange, _measuredSize, and _cachedConstraints.

Copilot · 2025-12-15T15:14:43Z

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

+	}
+}
+
+public class GroupHeaderTestAnimalGroup : ObservableCollection<GroupHeaderTestAnimal>


The class name GroupHeaderTestAnimalGroup is verbose and redundant. Following the naming pattern used in other test files (e.g., Issue12374Model), this should be named AnimalGroup or Issue33130AnimalGroup to be more concise while maintaining clarity.

Copilot · 2025-12-15T15:14:43Z

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

+	public ObservableCollection<GroupHeaderTestAnimalGroup> Animals { get; set; }
+
+	public GroupedAnimalsViewModel()
+	{
+		Animals = new ObservableCollection<GroupHeaderTestAnimalGroup>
+		{
+			new GroupHeaderTestAnimalGroup("Bears")
+			{
+				new GroupHeaderTestAnimal { Name = "Grizzly Bear", Location = "North America", ImageUrl = "bear.jpg" },
+				new GroupHeaderTestAnimal { Name = "Polar Bear", Location = "Arctic", ImageUrl = "bear.jpg" },
+			},
+			new GroupHeaderTestAnimalGroup("Monkeys")
+			{
+				new GroupHeaderTestAnimal { Name = "Baboon", Location = "Africa", ImageUrl = "monkey.jpg" },
+				new GroupHeaderTestAnimal { Name = "Capuchin Monkey", Location = "South America", ImageUrl = "monkey.jpg" },
+				new GroupHeaderTestAnimal { Name = "Spider Monkey", Location = "Central America", ImageUrl = "monkey.jpg" },
+			},
+			new GroupHeaderTestAnimalGroup("Elephants")
+			{
+				new GroupHeaderTestAnimal { Name = "African Elephant", Location = "Africa", ImageUrl = "elephant.jpg" },
+				new GroupHeaderTestAnimal { Name = "Asian Elephant", Location = "Asia", ImageUrl = "elephant.jpg" },
+			}
+		};
+	}
+}
+
+public class GroupHeaderTestAnimalGroup : ObservableCollection<GroupHeaderTestAnimal>
+{
+	public string Name { get; set; }
+
+	public GroupHeaderTestAnimalGroup(string name) : base()
+	{
+		Name = name;
+	}
+}
+
+public class GroupHeaderTestAnimal


The class name GroupHeaderTestAnimal is verbose with redundant "GroupHeaderTest" prefix. Following the naming pattern used in other test files (e.g., Issue12374Model), this should be named Animal or Issue33130Animal to be more concise while maintaining clarity.

Suggested change

public ObservableCollection<GroupHeaderTestAnimalGroup> Animals { get; set; }

public GroupedAnimalsViewModel()

{

Animals = new ObservableCollection<GroupHeaderTestAnimalGroup>

{

new GroupHeaderTestAnimalGroup("Bears")

{

new GroupHeaderTestAnimal { Name = "Grizzly Bear", Location = "North America", ImageUrl = "bear.jpg" },

new GroupHeaderTestAnimal { Name = "Polar Bear", Location = "Arctic", ImageUrl = "bear.jpg" },

},

new GroupHeaderTestAnimalGroup("Monkeys")

{

new GroupHeaderTestAnimal { Name = "Baboon", Location = "Africa", ImageUrl = "monkey.jpg" },

new GroupHeaderTestAnimal { Name = "Capuchin Monkey", Location = "South America", ImageUrl = "monkey.jpg" },

new GroupHeaderTestAnimal { Name = "Spider Monkey", Location = "Central America", ImageUrl = "monkey.jpg" },

},

new GroupHeaderTestAnimalGroup("Elephants")

{

new GroupHeaderTestAnimal { Name = "African Elephant", Location = "Africa", ImageUrl = "elephant.jpg" },

new GroupHeaderTestAnimal { Name = "Asian Elephant", Location = "Asia", ImageUrl = "elephant.jpg" },

}

};

}

}

public class GroupHeaderTestAnimalGroup : ObservableCollection<GroupHeaderTestAnimal>

{

public string Name { get; set; }

public GroupHeaderTestAnimalGroup(string name) : base()

{

Name = name;

}

}

public class GroupHeaderTestAnimal

public ObservableCollection<Issue33130AnimalGroup> Animals { get; set; }

public GroupedAnimalsViewModel()

{

Animals = new ObservableCollection<Issue33130AnimalGroup>

{

new Issue33130AnimalGroup("Bears")

{

new Issue33130Animal { Name = "Grizzly Bear", Location = "North America", ImageUrl = "bear.jpg" },

new Issue33130Animal { Name = "Polar Bear", Location = "Arctic", ImageUrl = "bear.jpg" },

},

new Issue33130AnimalGroup("Monkeys")

{

new Issue33130Animal { Name = "Baboon", Location = "Africa", ImageUrl = "monkey.jpg" },

new Issue33130Animal { Name = "Capuchin Monkey", Location = "South America", ImageUrl = "monkey.jpg" },

new Issue33130Animal { Name = "Spider Monkey", Location = "Central America", ImageUrl = "monkey.jpg" },

},

new Issue33130AnimalGroup("Elephants")

{

new Issue33130Animal { Name = "African Elephant", Location = "Africa", ImageUrl = "elephant.jpg" },

new Issue33130Animal { Name = "Asian Elephant", Location = "Asia", ImageUrl = "elephant.jpg" },

}

};

}

}

public class Issue33130AnimalGroup : ObservableCollection<Issue33130Animal>

{

public string Name { get; set; }

public Issue33130AnimalGroup(string name) : base()

{

Name = name;

}

}

public class Issue33130Animal

Copilot · 2025-12-15T15:14:44Z

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

+		var heightDifference = Math.Abs(headerRectBefore.Height - headerRectAfter.Height);
+
+		// Assert that the height difference is minimal (less than 5 pixels tolerance)
+		Assert.That(heightDifference, Is.EqualTo(0),


The assertion uses Is.EqualTo(0) which expects the height difference to be exactly zero. However, the comment on line 37 mentions "Allow for small rounding differences". This is inconsistent. If you want to allow for small rounding differences, the assertion should use a tolerance (e.g., Is.EqualTo(0).Within(1) or Is.LessThanOrEqualTo(1)) instead of requiring exact equality. As written, the test may fail due to minor floating-point precision differences across platforms.

Suggested change

Assert.That(heightDifference, Is.EqualTo(0),

Assert.That(heightDifference, Is.EqualTo(0).Within(5),

Copilot · 2025-12-15T15:14:44Z

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

 			{
 				TemplatedCell2.ScrollDirection = ScrollDirection;

+				// Ensure this cell is treated as a regular item cell (not a supplementary view)


The comment "Ensure this cell is treated as a regular item cell (not a supplementary view)" is helpful, but it would be more informative to explain why this is necessary. Consider expanding it to: "Ensure this cell is treated as a regular item cell (not a supplementary view) so it can use the cached first-item measurement for MeasureFirstItem strategy" to provide better context about the fix's purpose.

Suggested change

// Ensure this cell is treated as a regular item cell (not a supplementary view)

// Ensure this cell is treated as a regular item cell (not a supplementary view)

// so it can use the cached first-item measurement for MeasureFirstItem strategy

PureWeen · 2025-12-15T17:46:47Z

/backport to release/10.0.1xx-sr2

github-actions · 2025-12-15T17:46:56Z

Started backporting to release/10.0.1xx-sr2 (link to workflow run)

PureWeen · 2025-12-15T21:07:29Z

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

+                   Text="ItemSizingStrategy: MeasureAllItems"/>
+        </StackLayout>
+
+        <local:CollectionView2 Grid.Row="1"


Set this to just CollectionView if this is passing on both CV1 and CV2

Set this to just CollectionView if this is passing on both CV1 and CV2

Hi @PureWeen ,
I have changed CollectionView2 to CollectionView to ensure the test case passes on both CV1 and CV2.

@PureWeen

… size changes with ItemSizingStrategy (#33166) Backport of #33161 to release/10.0.1xx-sr2 /cc @PureWeen @NanthiniMahalingam --------- Co-authored-by: NanthiniMahalingam <[email protected]>

NanthiniMahalingam added 2 commits December 15, 2025 13:00

Fixed the header issue on first measure item.

21593dc

Updated the fix

db7834f

dotnet-policy-service bot added the partner/syncfusion Issues / PR's with Syncfusion collaboration label Dec 15, 2025

karthikraja-arumugam added the community ✨ Community Contribution label Dec 15, 2025

sheiksyedm added platform/ios area-controls-collectionview CollectionView, CarouselView, IndicatorView labels Dec 15, 2025

Added the test case

d9ac00e

NanthiniMahalingam force-pushed the fix-33130 branch from 035294e to d9ac00e Compare December 15, 2025 14:40

sheiksyedm marked this pull request as ready for review December 15, 2025 14:42

Copilot AI review requested due to automatic review settings December 15, 2025 14:42

Copilot started reviewing on behalf of sheiksyedm December 15, 2025 14:44 View session

Copilot AI reviewed Dec 15, 2025

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github-actions bot mentioned this pull request Dec 15, 2025

[release/10.0.1xx-sr2] [iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy #33166

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"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886

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PureWeen requested changes Dec 15, 2025

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Updated the test case.

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[iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy #33161

[iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy #33161

NanthiniMahalingam commented Dec 15, 2025 •

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	Assert.That(heightDifference, Is.EqualTo(0),
	Assert.That(heightDifference, Is.EqualTo(0).Within(5),

	// Ensure this cell is treated as a regular item cell (not a supplementary view)
	// Ensure this cell is treated as a regular item cell (not a supplementary view)
	// so it can use the cached first-item measurement for MeasureFirstItem strategy

[iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy #33161

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[iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy #33161

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NanthiniMahalingam commented Dec 15, 2025 •

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