How to get a TextBlock to wrap text inside a DockPanel area? - silverlight

Question

What do I have to do to get the inner TextBlock below to wrap its text without defining an absolute width?
I've tried Width=Auto, Stretch, TextWrapping, putting it in a StackPanel, nothing seems to work.
(source: deviantsart.com)
XAML:
<UserControl x:Class="Test5.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:tk="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Toolkit"
Width="800"
Height="600">
<tk:DockPanel LastChildFill="True">
<StackPanel tk:DockPanel.Dock="Top"
Width="Auto"
Height="50"
Background="#eee">
<TextBlock Text="{Binding TopContent}"/>
</StackPanel>
<StackPanel tk:DockPanel.Dock="Bottom" Background="#bbb"
Width="Auto"
Height="50">
<TextBlock Text="bottom area"/>
</StackPanel>
<StackPanel tk:DockPanel.Dock="Right" Background="#ccc"
Width="200"
Height="Auto">
<TextBlock Text="info panel"/>
</StackPanel>
<StackPanel tk:DockPanel.Dock="Left" Background="#ddd"
Width="Auto"
Height="Auto">
<ScrollViewer HorizontalScrollBarVisibility="Auto" Padding="10"
BorderThickness="0"
Width="Auto"
VerticalScrollBarVisibility="Auto">
<tk:DockPanel HorizontalAlignment="Left" Width="Auto" >
<StackPanel tk:DockPanel.Dock="Top" HorizontalAlignment="Left">
<Button Content="Add More" Click="Button_Click"/>
</StackPanel>
<TextBlock tk:DockPanel.Dock="Top"
Text="{Binding MainContent}"
Width="Auto"
TextWrapping="Wrap" />
</tk:DockPanel>
</ScrollViewer>
</StackPanel>
</tk:DockPanel>
</UserControl>

Answer 1

Have you tried changing the scrollbar visibility?
<ScrollViewer HorizontalScrollBarVisibility="Disabled" Padding="10"
BorderThickness="0"
Width="Auto"
VerticalScrollBarVisibility="Auto">

Answer 2

For some reason the obvious (elegant) solution doesn't seem to work in SL:
<ScrollViewer Name="w_scrollViewer" HorizontalScrollBarVisibility="Auto" Padding="10"
BorderThickness="0" Width="Auto" VerticalScrollBarVisibility="Auto">
<tk:DockPanel Name="w_dp" HorizontalAlignment="Left" Width="Auto" >
<TextBlock Margin="2" Name="w_tb"
Text="{Binding MainContent}" TextWrapping="Wrap"
Width="{Binding ActualWidth, ElementName=w_scrollViewer}"
/>
</tk:DockPanel>
</ScrollViewer>
but a bit more "rough" way:
<StackPanel SizeChanged="w_sp_SizeChanged" Name="w_sp" tk:DockPanel.Dock="Left"
Background="#ddd" Width="Auto" Height="Auto">
<ScrollViewer Name="w_scrollViewer" HorizontalScrollBarVisibility="Auto"
Padding="10" Width="Auto" VerticalScrollBarVisibility="Auto"
SizeChanged="HandleScrollViewerSizeChanged" >
<tk:DockPanel HorizontalAlignment="Left" Width="Auto" >
<TextBlock Name="w_textBlock" Text="{Binding MainContent}" TextWrapping="Wrap" />
</tk:DockPanel>
</ScrollViewer>
</StackPanel>
code behind:
private void HandleScrollViewerSizeChanged(object sender, SizeChangedEventArgs e)
{
w_textBlock.Width = w_scrollViewer.ActualWidth;
}