Horizontal Scrollbars on a Fluid Listbox - silverlight

Question

What I want: To get the darn horizontal scrollbar to appear. I will be editing it a bit just so i fits the rest of the app's style scheme, but not too much.
What I have
Here is the code for the listbox as of now. Everything runs perfectly except the scrollbars dont appear. You might say... "well you dont have a scrollviewer anywhere", but I have tried inserting a scrollviewer in numerous places and still no luck.
The Listbox Code:
<ListBox ItemsSource="{Binding Items}" ItemTemplate="{StaticResource itemsdatatemplate}" Background="{x:Null}" BorderBrush="{x:Null}" Foreground="{x:Null}" ItemsPanel="{StaticResource HorizontalListBoxTemplate}" ItemContainerStyle="{StaticResource TransparentListBox}" VerticalAlignment="Center" SelectedItem="{Binding SelectedItem, Mode=TwoWay}" />
The 'TransparentListBox' (to shut-up the selected background color):
<Style x:Key="TransparentListBox" TargetType="ListBoxItem">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ListBoxItem">
<Grid>
<Border x:Name="HoverBorderBackgroundBrush" BorderThickness="1" Margin="0,0,25,0" Background="Transparent"/>
<Border x:Name="SelectedBorderBackgroundBrush" BorderThickness="1" Margin="0,0,25,0" Background="Transparent"/>
<ContentPresenter></ContentPresenter>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Horizontal List Box (to make the listbox Horizontal, rather than standard vertical)
<ItemsPanelTemplate x:Key="HorizontalListBoxTemplate">
<StackPanel Orientation="Horizontal">
</StackPanel>
</ItemsPanelTemplate>
The Datatemplate (to actually show the Items)
<DataTemplate x:Key="itemsdatatemplate">
<local:ListItemControl HorizontalAlignment="Left" VerticalAlignment="Top" DataContext="{Binding}"/>
</DataTemplate>
I have a feeling its going to be a simple addition, but Thanks in advance.
Update
It looks like the scrollbars now do appear with this:
<Style x:Key="ScrollingListBox" TargetType="ListBox">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<Grid>
<ScrollViewer HorizontalScrollBarVisibility="Visible">
<ItemsPresenter></ItemsPresenter>
</ScrollViewer>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
But they do not function accordingly. They feel... broken. However, if one was to define a static width (say 300) of the grid, then the ScrollViewer acts perfectly. Right now I have a completely fluid layout (meaning things stretch to fill), is this not acceptable for scrollviewers?

Answer 1

When you create your own template, you have to define the ScrollViewer in there and use an ItemPresenter instead of a ContentPresenter.
<Style x:Key="TransparentListBox" TargetType="ListBoxItem">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ListBoxItem">
<Grid>
<Border x:Name="HoverBorderBackgroundBrush" BorderThickness="1" Margin="0,0,25,0" Background="Transparent"/>
<Border x:Name="SelectedBorderBackgroundBrush" BorderThickness="1" Margin="0,0,25,0" Background="Transparent"/>
<ScrollViewer x:Name="ScrollViewer" HorizontalScrollBarVisibility="Visible">
<ItemsPresenter />
</ScrollViewer>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>