Fix WrapPanel stretching behavior for last item

components/Primitives/src/WrapPanel/WrapPanel.cs

@@ -97,6 +97,12 @@ public Thickness Padding
     /// <summary>
     /// Gets or sets a value indicating how to arrange child items
     /// </summary>
+    /// <remarks>
+    /// When the available size provided to the panel is infinite (for example,
+    /// when placed in a container with Auto sizing), the last child will not be
+    /// stretched. Attempting to stretch in this scenario would cause the element
+    /// to expand to an infinite size and result in a runtime exception.
+    /// </remarks>
     public StretchChild StretchChild
     {
         get { return (StretchChild)GetValue(StretchChildProperty); }
@@ -219,7 +225,8 @@ void Arrange(UIElement child, bool isLast = false)
             }
 
             // Stretch the last item to fill the available space
-            if (isLast)
+            // if the parent measure is not infinite
+            if (isLast && !double.IsInfinity(parentMeasure.U))
             {
                 desiredMeasure.U = parentMeasure.U - position.U;
             }

components/Primitives/tests/Primitives.Tests.projitems

@@ -33,10 +33,23 @@
     <Compile Include="$(MSBuildThisFileDirectory)Test_UniformGrid_FreeSpots.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_UniformGrid_RowColDefinitions.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_WrapPanel_BasicLayout.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Test_WrapPanel_StretchChild.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Test_WrapPanel_Visibility.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)UniformGrid\AutoLayoutFixedElementZeroZeroSpecialPage.xaml.cs">
       <DependentUpon>AutoLayoutFixedElementZeroZeroSpecialPage.xaml</DependentUpon>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)WrapPanel\HorizontalWrapPanelInsideParentWithInfinityWidth.xaml.cs">
+      <DependentUpon>HorizontalWrapPanelInsideParentWithInfinityWidth.xaml</DependentUpon>
+    </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)WrapPanel\HorizontalWrapPanelInsideParentWithLimitedWidth.xaml.cs">
+      <DependentUpon>HorizontalWrapPanelInsideParentWithLimitedWidth.xaml</DependentUpon>
+    </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)WrapPanel\VerticalWrapPanelInsideParentWithInfinityHeight.xaml.cs">
+      <DependentUpon>VerticalWrapPanelInsideParentWithInfinityHeight.xaml</DependentUpon>
+    </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)WrapPanel\VerticalWrapPanelInsideParentWithLimitedHeight.xaml.cs">
+      <DependentUpon>VerticalWrapPanelInsideParentWithLimitedHeight.xaml</DependentUpon>
+    </Compile>
   </ItemGroup>
   <ItemGroup>
     <Page Include="$(MSBuildThisFileDirectory)DockPanel\DockPanelSample.xaml">
@@ -47,6 +60,22 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="$(MSBuildThisFileDirectory)WrapPanel\HorizontalWrapPanelInsideParentWithInfinityWidth.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
+    <Page Include="$(MSBuildThisFileDirectory)WrapPanel\HorizontalWrapPanelInsideParentWithLimitedWidth.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
+    <Page Include="$(MSBuildThisFileDirectory)WrapPanel\VerticalWrapPanelInsideParentWithInfinityHeight.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
+    <Page Include="$(MSBuildThisFileDirectory)WrapPanel\VerticalWrapPanelInsideParentWithLimitedHeight.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
   </ItemGroup>
   <ItemGroup>
     <Page Include="$(MSBuildThisFileDirectory)SwitchPresenter\SwitchConverterBrushSample.xaml">

components/Primitives/tests/Test_WrapPanel_StretchChild.cs

@@ -0,0 +1,104 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using CommunityToolkit.Tests;
+using CommunityToolkit.Tooling.TestGen;
+using CommunityToolkit.WinUI.Controls;
+
+namespace PrimitivesTests;
+
+[TestClass]
+public partial class Test_WrapPanel_StretchChild : VisualUITestBase
+{
+    /// <summary>
+    /// When a WrapPanel is inside a parent with infinite width, the last child cannot stretch to fill the remaining space.
+    /// Instead, it should measure to its desired size.
+    /// </summary>
+    [TestCategory("WrapPanel")]
+    [UIThreadTestMethod]
+    public void VerticalWrapPanelInsideParentWithInfinityHeightTest(VerticalWrapPanelInsideParentWithInfinityHeight page)
+    {
+        var wrapPanel = page.FindDescendant<WrapPanel>();
+        Assert.IsNotNull(wrapPanel, "Could not find WrapPanel.");
+        Assert.IsFalse(wrapPanel.StretchChild is not StretchChild.Last, "WrapPanel StretchChild property not set to Last.");
+        Assert.IsFalse(wrapPanel.Children.Count < 1, "No children to test.");
+
+        foreach (var child in wrapPanel.Children.Cast<FrameworkElement>())
+        {
+            double expectedHeight = child.DesiredSize.Height;
+            Assert.AreEqual(expectedHeight, child.ActualHeight, "Child height not as expected.");
+        }
+    }
+
+    /// <summary>
+    /// When a WrapPanel is inside a parent with limited height, the last child with Stretch alignment should fill the remaining space.
+    /// </summary>
+    [TestCategory("WrapPanel")]
+    [UIThreadTestMethod]
+    public void VerticalWrapPanelInsideParentWithLimitedHeightTest(VerticalWrapPanelInsideParentWithLimitedHeight page)
+    {
+        var wrapPanel = page.FindDescendant<WrapPanel>();
+        Assert.IsNotNull(wrapPanel, "Could not find WrapPanel.");
+        Assert.IsFalse(wrapPanel.StretchChild is not StretchChild.Last, "WrapPanel StretchChild property not set to Last.");
+        Assert.IsFalse(wrapPanel.Children.Count < 1, "No children to test.");
+
+        var precedingChildren = wrapPanel.Children.Cast<FrameworkElement>().Take(wrapPanel.Children.Count - 1);
+
+        foreach (var child in precedingChildren)
+        {
+            double expectedHeight = child.DesiredSize.Height;
+            Assert.AreEqual(expectedHeight, child.ActualHeight, "Preceding child height not as expected.");
+        }
+
+        var lastChild = wrapPanel.Children.Cast<FrameworkElement>().Last();
+        double lastChildExpectedHeight = wrapPanel.ActualHeight - precedingChildren.Sum(child => child.ActualHeight);
+        Assert.AreEqual(lastChildExpectedHeight, lastChild.ActualHeight, "Last child height not as expected.");
+    }
+
+    /// <summary>
+    /// When a WrapPanel is inside a parent with infinite width, the last child cannot stretch to fill the remaining space.
+    /// Instead, it should measure to its desired size.
+    /// </summary>
+    [TestCategory("WrapPanel")]
+    [UIThreadTestMethod]
+    public void HorizontalWrapPanelInsideParentWithInfinityWidthTest(HorizontalWrapPanelInsideParentWithInfinityWidth page)
+    {
+        var wrapPanel = page.FindDescendant<WrapPanel>();
+        Assert.IsNotNull(wrapPanel, "Could not find WrapPanel.");
+        Assert.IsFalse(wrapPanel.StretchChild is not StretchChild.Last, "WrapPanel StretchChild property not set to Last.");
+        Assert.IsFalse(wrapPanel.Children.Count < 1, "No children to test.");
+
+        foreach (var child in wrapPanel.Children.Cast<FrameworkElement>())
+        {
+            double expectedWidth = child.DesiredSize.Width;
+            Assert.AreEqual(expectedWidth, child.ActualWidth, "Preceding child width not as expected.");
+        }
+    }
+
+    /// <summary>
+    /// When a WrapPanel is inside a parent with limited width, the last child with Stretch alignment should fill the remaining space.
+    /// </summary>
+    /// <param name="page"></param>
+    [TestCategory("WrapPanel")]
+    [UIThreadTestMethod]
+    public void HorizontalWrapPanelInsideParentWithLimitedWidthTest(HorizontalWrapPanelInsideParentWithLimitedWidth page)
+    {
+        var wrapPanel = page.FindDescendant<WrapPanel>();
+        Assert.IsNotNull(wrapPanel, "Could not find WrapPanel.");
+        Assert.IsFalse(wrapPanel.StretchChild is not StretchChild.Last, "WrapPanel StretchChild property not set to Last.");
+        Assert.IsFalse(wrapPanel.Children.Count < 1, "No children to test.");
+
+        var precedingChildren = wrapPanel.Children.Cast<FrameworkElement>().Take(wrapPanel.Children.Count - 1);
+
+        foreach (var child in precedingChildren)
+        {
+            double expectedWidth = child.DesiredSize.Width;
+            Assert.AreEqual(expectedWidth, child.ActualWidth, "Child width not as expected.");
+        }
+
+        var lastChild = wrapPanel.Children.Cast<FrameworkElement>().Last();
+        double lastChildExpectedWidth = wrapPanel.ActualWidth - precedingChildren.Sum(child => child.ActualWidth);
+        Assert.AreEqual(lastChildExpectedWidth, lastChild.ActualWidth, "Last child width not as expected.");
+    }
+}

components/Primitives/tests/WrapPanel/HorizontalWrapPanelInsideParentWithInfinityWidth.xaml

@@ -0,0 +1,26 @@
+<Page x:Class="PrimitivesTests.HorizontalWrapPanelInsideParentWithInfinityWidth"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:controls="using:CommunityToolkit.WinUI.Controls"
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+      xmlns:local="using:PrimitivesTests"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
+      mc:Ignorable="d">
+
+    <Grid>
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="Auto" />
+        </Grid.ColumnDefinitions>
+        <controls:WrapPanel Orientation="Horizontal"
+                            StretchChild="Last">
+            <Button HorizontalAlignment="Stretch"
+                    Content="Child 1" />
+            <Button HorizontalAlignment="Stretch"
+                    Content="Child 2" />
+            <Button HorizontalAlignment="Stretch"
+                    Content="Last Child" />
+        </controls:WrapPanel>
+    </Grid>
+
+</Page>

components/Primitives/tests/WrapPanel/HorizontalWrapPanelInsideParentWithInfinityWidth.xaml.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace PrimitivesTests;
+
+public sealed partial class HorizontalWrapPanelInsideParentWithInfinityWidth : Page
+{
+    public HorizontalWrapPanelInsideParentWithInfinityWidth()
+    {
+        this.InitializeComponent();
+    }
+}

components/Primitives/tests/WrapPanel/HorizontalWrapPanelInsideParentWithLimitedWidth.xaml

@@ -0,0 +1,26 @@
+<Page x:Class="PrimitivesTests.HorizontalWrapPanelInsideParentWithLimitedWidth"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:controls="using:CommunityToolkit.WinUI.Controls"
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+      xmlns:local="using:PrimitivesTests"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
+      mc:Ignorable="d">
+
+    <Grid>
+        <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="*" />
+        </Grid.ColumnDefinitions>
+        <controls:WrapPanel Orientation="Horizontal"
+                            StretchChild="Last">
+            <Button HorizontalAlignment="Stretch"
+                    Content="Child 1" />
+            <Button HorizontalAlignment="Stretch"
+                    Content="Child 2" />
+            <Button HorizontalAlignment="Stretch"
+                    Content="Last Child" />
+        </controls:WrapPanel>
+    </Grid>
+
+</Page>

components/Primitives/tests/WrapPanel/HorizontalWrapPanelInsideParentWithLimitedWidth.xaml.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace PrimitivesTests;
+
+public sealed partial class HorizontalWrapPanelInsideParentWithLimitedWidth : Page
+{
+    public HorizontalWrapPanelInsideParentWithLimitedWidth()
+    {
+        this.InitializeComponent();
+    }
+}

components/Primitives/tests/WrapPanel/VerticalWrapPanelInsideParentWithInfinityHeight.xaml

@@ -0,0 +1,26 @@
+<Page x:Class="PrimitivesTests.VerticalWrapPanelInsideParentWithInfinityHeight"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:controls="using:CommunityToolkit.WinUI.Controls"
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+      xmlns:local="using:PrimitivesTests"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
+      mc:Ignorable="d">
+
+    <Grid>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto" />
+        </Grid.RowDefinitions>
+        <controls:WrapPanel Orientation="Vertical"
+                            StretchChild="Last">
+            <Button VerticalAlignment="Stretch"
+                    Content="Child 1" />
+            <Button VerticalAlignment="Stretch"
+                    Content="Child 2" />
+            <Button VerticalAlignment="Stretch"
+                    Content="Last Child" />
+        </controls:WrapPanel>
+    </Grid>
+
+</Page>

components/Primitives/tests/WrapPanel/VerticalWrapPanelInsideParentWithInfinityHeight.xaml.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace PrimitivesTests;
+
+public sealed partial class VerticalWrapPanelInsideParentWithInfinityHeight : Page
+{
+    public VerticalWrapPanelInsideParentWithInfinityHeight()
+    {
+        this.InitializeComponent();
+    }
+}

components/Primitives/tests/WrapPanel/VerticalWrapPanelInsideParentWithLimitedHeight.xaml

@@ -0,0 +1,26 @@
+<Page x:Class="PrimitivesTests.VerticalWrapPanelInsideParentWithLimitedHeight"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:controls="using:CommunityToolkit.WinUI.Controls"
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+      xmlns:local="using:PrimitivesTests"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
+      mc:Ignorable="d">
+
+    <Grid>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="*" />
+        </Grid.RowDefinitions>
+        <controls:WrapPanel Orientation="Vertical"
+                            StretchChild="Last">
+            <Button VerticalAlignment="Stretch"
+                    Content="Child 1" />
+            <Button VerticalAlignment="Stretch"
+                    Content="Child 2" />
+            <Button VerticalAlignment="Stretch"
+                    Content="Last Child" />
+        </controls:WrapPanel>
+    </Grid>
+
+</Page>

components/Primitives/tests/WrapPanel/VerticalWrapPanelInsideParentWithLimitedHeight.xaml.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace PrimitivesTests;
+
+public sealed partial class VerticalWrapPanelInsideParentWithLimitedHeight : Page
+{
+    public VerticalWrapPanelInsideParentWithLimitedHeight()
+    {
+        this.InitializeComponent();
+    }
+}