ItemsControl中带SharedSizeGroup的列无法占满可用宽度

青色区域是ItemsControl的背景，可见它已经占据了整个窗口宽度。我希望中间显示“unknown”的列能够水平拉伸，但始终无法实现，不清楚遗漏了什么设置。

<GroupBox Grid.Row="1" BorderThickness="2" BorderBrush="Black">
    <ItemsControl Background="Aquamarine"
        ItemsSource="{Binding
            RelativeSource={RelativeSource AncestorType={x:Type local:AppGroup}},
            Path=AppItemSource}"
        Grid.IsSharedSizeScope="True"
        HorizontalContentAlignment="Stretch">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto" SharedSizeGroup="Name"/>
                        <ColumnDefinition Width="*" SharedSizeGroup="State"/>
                        <ColumnDefinition Width="Auto" SharedSizeGroup="Buttons"/>
                    </Grid.ColumnDefinitions>
                    <TextBlock Style="{StaticResource AppNameColumnText}" Grid.Column="0" Text="{Binding Name}"/>
                    <TextBlock Style="{StaticResource AppStateColumnText}" Grid.Column="1" Text="{Binding StatusText}" TextAlignment="Center" HorizontalAlignment="Stretch"/>
                    <StackPanel Grid.Column="2" Orientation="Horizontal">
                        <StackPanel.Resources>
                            <Style TargetType="Button">
                                <Setter Property="Width" Value="20"/>
                                <Setter Property="Height" Value="20"/>
                                <Setter Property="Margin" Value="5"/>
                            </Style>
                        </StackPanel.Resources>
                        
                        <Button Style="{StaticResource StartButton}" Command="{Binding StartCommand}"/>
                        <Button Style="{StaticResource StopButton}" Command="{Binding StopCommand}"/>
                    </StackPanel>
                </Grid>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>
</GroupBox>

• 将ItemsControl的HorizontalContentAlignment设为Stretch
• 中间列宽度定义为*
• 允许TextBlock拉伸

<Style x:Key="AppNameColumnText" TargetType="TextBlock">
    <Setter Property="Margin" Value="20,0,20,0"/>
    <Setter Property="FontSize" Value="26"/>
</Style>
<Style x:Key="AppStateColumnText" TargetType="TextBlock">
    <Setter Property="Margin" Value="20,0,20,0"/>
    <Setter Property="FontSize" Value="26"/>
</Style>

问题出在两个核心设置上：

1. SharedSizeGroup与*宽度冲突：给中间列设置的SharedSizeGroup="State"会强制列宽统一为所有行中该列内容的最大宽度，完全覆盖*的拉伸规则。需要移除中间列的SharedSizeGroup属性。
2. 项容器未水平拉伸：ItemsControl的默认项容器（ContentPresenter）默认左对齐，即使ItemsControl设置了HorizontalContentAlignment="Stretch"，容器本身也不会占满控件宽度，导致内部Grid无法拉伸。需要添加ItemContainerStyle让容器水平拉伸。

修改后的ItemsControl代码如下：

<ItemsControl Background="Aquamarine"
    ItemsSource="{Binding
        RelativeSource={RelativeSource AncestorType={x:Type local:AppGroup}},
        Path=AppItemSource}"
    Grid.IsSharedSizeScope="True"
    HorizontalContentAlignment="Stretch">
    <!-- 添加ItemContainerStyle，让项容器水平拉伸 -->
    <ItemsControl.ItemContainerStyle>
        <Style TargetType="ContentPresenter">
            <Setter Property="HorizontalAlignment" Value="Stretch"/>
        </Style>
    </ItemsControl.ItemContainerStyle>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="Auto" SharedSizeGroup="Name"/>
                    <!-- 移除中间列的SharedSizeGroup -->
                    <ColumnDefinition Width="*"/>
                    <ColumnDefinition Width="Auto" SharedSizeGroup="Buttons"/>
                </Grid.ColumnDefinitions>
                <TextBlock Style="{StaticResource AppNameColumnText}" Grid.Column="0" Text="{Binding Name}"/>
                <TextBlock Style="{StaticResource AppStateColumnText}" Grid.Column="1" Text="{Binding StatusText}" TextAlignment="Center" HorizontalAlignment="Stretch"/>
                <StackPanel Grid.Column="2" Orientation="Horizontal">
                    <StackPanel.Resources>
                        <Style TargetType="Button">
                            <Setter Property="Width" Value="20"/>
                            <Setter Property="Height" Value="20"/>
                            <Setter Property="Margin" Value="5"/>
                        </Style>
                    </StackPanel.Resources>
                    
                    <Button Style="{StaticResource StartButton}" Command="{Binding StartCommand}"/>
                    <Button Style="{StaticResource StopButton}" Command="{Binding StopCommand}"/>
                </StackPanel>
            </Grid>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

内容的提问来源于stack exchange，提问作者bas