Stretch ComboBox Content in Silverlight - xaml

Question

This is driving me nuts. I can't seem to get the data template within my ComboBox to stretch the width of the pulldown. What gives?
<Grid x:Name="LayoutRoot" Background="White">
<Grid.RowDefinitions>
<RowDefinition Height="30" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<ComboBox x:Name="SearchesComboBox" HorizontalContentAlignment="Stretch" Width="150">
<ComboBox.ItemContainerStyle>
<Style TargetType="ComboBoxItem">
<Setter Property="HorizontalContentAlignment" Value="Stretch"/>
</Style>
</ComboBox.ItemContainerStyle>
<ComboBox.ItemTemplate>
<DataTemplate>
<Border BorderBrush="Black" BorderThickness="1">
<TextBlock Text="{Binding}" Margin="2" />
</Border>
</DataTemplate>
</ComboBox.ItemTemplate>
<sys:String>Two</sys:String>
<sys:String>Four</sys:String>
<sys:String>Six</sys:String>
</ComboBox>
</Grid>

Answer 1

<ComboBox.ItemContainerStyle>
<Style TargetType="ComboBoxItem">
<Setter Property="HorizontalContentAlignment" Value="Stretch"/>
</Style>
</ComboBox.ItemContainerStyle>

Answer 2

I just confirmed the following works in WPF, moving the HorizontalContentAlignment up to the ComboBox:
<ComboBox x:Name="SearchesComboBox" HorizontalContentAlignment="Stretch" Width="150">
<ComboBox.ItemTemplate>
<DataTemplate>
<Border BorderBrush="Black" BorderThickness="1">
<TextBlock Text="{Binding}" Margin="2" />
</Border>
</DataTemplate>
</ComboBox.ItemTemplate>
<sys:String>Two</sys:String>
<sys:String>Four</sys:String>
<sys:String>Six</sys:String>
</ComboBox>
Let me know if this also fixes the problem in Silverlight. The issue as I was seeing it was the items in the drop-down were correctly sized, while the content that showed in the pull-down was not stretching.

Answer 3

Ok, after about a day of fiddling with it, I have a solution. I HATE it, but it works. Basically, I reflected into the System.Windows.dll for Silverlight, and I ripped out the default template for ListBoxItem (which ComboBoxItem uses).
It turns out that in that template, there is a ContentPresenter with the HorizontalAlignment hard-coded to Left. So, I ripped off the template, and added a TemplateBinding for HorizontalAlignment, so it can use whatever the HorizontalAlignment of ComboBoxItem is.
That being said, what follows is the working code. If ANYONE has a better way to do this, please tell me. I haven't checked yet if this is fixed in 3.0. I hope it is. It should really bind all the way from ComboBox.HorizontalContentAlignment.
<UserControl.Resources>
<Style x:Key="FixedComboBoxItem" TargetType="ComboBoxItem">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBoxItem">
<Grid Background="{TemplateBinding Background}">
<vsm:VisualStateManager.VisualStateGroups>
<vsm:VisualStateGroup x:Name="CommonStates">
<vsm:VisualState x:Name="Normal" />
<vsm:VisualState x:Name="MouseOver">
<Storyboard>
<DoubleAnimation Storyboard.TargetName="fillColor" Storyboard.TargetProperty="Opacity" Duration="0" To=".35"/>
</Storyboard>
</vsm:VisualState>
<vsm:VisualState x:Name="Disabled">
<Storyboard>
<DoubleAnimation Storyboard.TargetName="contentPresenter" Storyboard.TargetProperty="Opacity" Duration="0" To=".55" />
</Storyboard>
</vsm:VisualState>
</vsm:VisualStateGroup>
<vsm:VisualStateGroup x:Name="SelectionStates">
<vsm:VisualState x:Name="Unselected" />
<vsm:VisualState x:Name="Selected">
<Storyboard>
<DoubleAnimation Storyboard.TargetName="fillColor2" Storyboard.TargetProperty="Opacity" Duration="0" To=".75"/>
</Storyboard>
</vsm:VisualState>
</vsm:VisualStateGroup>
<vsm:VisualStateGroup x:Name="FocusStates">
<vsm:VisualState x:Name="Focused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetName="FocusVisualElement" Storyboard.TargetProperty="Visibility" Duration="0">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Visible</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</vsm:VisualState>
<vsm:VisualState x:Name="Unfocused"/>
</vsm:VisualStateGroup>
</vsm:VisualStateManager.VisualStateGroups>
<Rectangle x:Name="fillColor" Opacity="0" Fill="#FFBADDE9" IsHitTestVisible="False" RadiusX="1" RadiusY="1"/>
<Rectangle x:Name="fillColor2" Opacity="0" Fill="#FFBADDE9" IsHitTestVisible="False" RadiusX="1" RadiusY="1"/>
<ContentPresenter
x:Name="contentPresenter"
Content="{TemplateBinding Content}"
ContentTemplate="{TemplateBinding ContentTemplate}"
HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
Margin="{TemplateBinding Padding}"/>
<Rectangle x:Name="FocusVisualElement" Stroke="#FF6DBDD1" StrokeThickness="1" Visibility="Collapsed" RadiusX="1" RadiusY="1" />
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</UserControl.Resources>
<Grid x:Name="LayoutRoot" Background="White">
<Grid.RowDefinitions>
<RowDefinition Height="30" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<ComboBox x:Name="SearchesComboBox" Width="150" ItemContainerStyle="{StaticResource FixedComboBoxItem}" HorizontalContentAlignment="Stretch">
<ComboBox.ItemTemplate>
<DataTemplate>
<Border BorderBrush="Black" BorderThickness="1" >
<TextBlock Text="{Binding}" Margin="2" />
</Border>
</DataTemplate>
</ComboBox.ItemTemplate>
<sys:String>Two</sys:String>
<sys:String>Four</sys:String>
<sys:String>Six</sys:String>
</ComboBox>
</Grid>