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[Windows] Fix LineHeight values < 1 having no effect by setting LineStackingStrategy to BlockLineHeight #31219

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[Windows] Fix LineHeight values < 1 having no effect by setting LineStackingStrategy to BlockLineHeight #31219

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d7fa535
Initial plan
Copilot Aug 18, 2025
454bfe0
Fix LineStackingStrategy for Windows Labels to support LineHeight < 1
Copilot Aug 18, 2025
6045060
Enable Windows LineHeight tests and add missing GetNative methods
Copilot Aug 18, 2025
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2 changes: 2 additions & 0 deletions src/Core/src/Platform/Windows/TextBlockExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
using System.Xml;
using System.Xml.Linq;
using System.Xml.Resolvers;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Documents;
using WThickness = Microsoft.UI.Xaml.Thickness;
Expand Down Expand Up @@ -70,6 +71,7 @@ public static void UpdateLineHeight(this TextBlock platformControl, ILabel label
if (label.LineHeight >= 0)
{
platformControl.LineHeight = label.LineHeight * platformControl.FontSize;
platformControl.LineStackingStrategy = LineStackingStrategy.BlockLineHeight;
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@MartyIX MartyIX Aug 18, 2025

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I wonder if it would be better to set some default style here: https://github.com/dotnet/maui/blob/main/src/Core/src/Platform/Windows/Styles/Resources.xaml. The idea being that performance of the application would be better because the XAML would be set once and not for each and every label that sets some line height.

}
}

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46 changes: 46 additions & 0 deletions src/Core/tests/DeviceTests/Handlers/Label/LabelHandlerTests.Windows.cs
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Expand Up @@ -3,6 +3,7 @@
using System.Threading.Tasks;
using Microsoft.Maui.DeviceTests.Stubs;
using Microsoft.Maui.Storage;
using Microsoft.UI.Xaml;
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@MartyIX MartyIX Aug 19, 2025

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It would be good to add a UI test containing

		<!-- Exercise line heights less than 1. --> 
		<Label BackgroundColor="Green" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Red" LineHeight="0.8" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Green" LineHeight="0.2" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Red" LineHeight="0.4" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Green" LineHeight="1.0" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Red" LineHeight="1.2" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Green" LineHeight="1.4" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Red" LineHeight="1.6" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Green" LineHeight="2.0" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
		<Label BackgroundColor="Red" LineHeight="4.6" FontSize="20" Text="ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ"/>
	</VerticalStackLayout>

from the comment #24520 (comment)

using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Media;
using Xunit;
Expand Down Expand Up @@ -101,5 +102,50 @@ Color GetNativeTextColor(LabelHandler labelHandler)

UI.Xaml.TextAlignment GetNativeHorizontalTextAlignment(LabelHandler labelHandler) =>
GetPlatformLabel(labelHandler).TextAlignment;

double GetNativeLineHeight(LabelHandler labelHandler) =>
GetPlatformLabel(labelHandler).LineHeight;

double GetNativeCharacterSpacing(LabelHandler labelHandler) =>
GetPlatformLabel(labelHandler).CharacterSpacing;

[Fact]
public async Task LineHeightSetsLineStackingStrategyToBlockLineHeight()
{
var label = new LabelStub
{
Text = "Test text with line height",
LineHeight = 0.8 // LineHeight less than 1
};

var (lineHeight, lineStackingStrategy) = await GetValueAsync(label, handler =>
{
var platformLabel = GetPlatformLabel(handler);
return (platformLabel.LineHeight, platformLabel.LineStackingStrategy);
});

// When LineHeight is set, LineStackingStrategy should be BlockLineHeight
Assert.Equal(LineStackingStrategy.BlockLineHeight, lineStackingStrategy);
Assert.True(lineHeight > 0, "LineHeight should be greater than 0 when set");
}

[Fact]
public async Task NoLineHeightDefaultLineStackingStrategy()
{
var label = new LabelStub
{
Text = "Test text without line height"
// LineHeight not set (default is -1)
};

var lineStackingStrategy = await GetValueAsync(label, handler =>
{
var platformLabel = GetPlatformLabel(handler);
return platformLabel.LineStackingStrategy;
});

// When LineHeight is not set, LineStackingStrategy should remain default (MaxHeight)
Assert.Equal(LineStackingStrategy.MaxHeight, lineStackingStrategy);
}
}
}
3 changes: 0 additions & 3 deletions src/Core/tests/DeviceTests/Handlers/Label/LabelHandlerTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -208,8 +208,6 @@ await ValidateUnrelatedPropertyUnaffected(
() => label.TextDecorations = newDecorations);
}

#if !WINDOWS

[Fact]
[Category(TestCategory.TextFormatting)]
public async Task LineHeightAppliedWhenTextAdded()
Expand Down Expand Up @@ -296,7 +294,6 @@ public async Task LineHeightInitializesCorrectly()
Assert.Equal(xplatLineHeight, values.ViewValue);
Assert.Equal(expectedValue, values.PlatformViewValue);
}
#endif

[Fact(DisplayName = "Html Text Initializes Correctly")]
public async Task HtmlTextInitializesCorrectly()
Expand Down