WPF TextBox Wrapping - wpf

Question

I am trying to figure out how to get a textbox to wrap its contents, however the situation isn't quite the same as the typical "it doesn't wrap" scenario. My textbox is contained inside a DataTemplate which is used inside a Telerik RadTabControl instance (using a ContentTemplatePresenter to determine which view to display) and the XAML for the DataTemplate looks like this:
<DataTemplate x:Key="NotesTemplate">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<TextBlock Text="Use the box below to record any general notes associated with this item." Style="{StaticResource Default}" />
<TextBox TextWrapping="Wrap" AcceptsReturn="True" VerticalScrollBarVisibility="Auto" GridRow="1" Margin="20" Text="{Binding Notes, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
</DataTemplate>
The reason I say it doesn't fall under the normal "it doesn't wrap" scenario is it used to wrap until I had to change the view to be resizable to anything to support the varying screen sizes the app will be run on. When I did that the TextBox stopped wrapping because (presumably) as the user types something the TextBox says "I need more space" so the parent obliges and the box continues out to the right indefinitely (although the view gets scrollbars). I tried setting a MaxWidth using Binding/RelativeSource, but since the parent is specifically designed to grow that approach won't work. What I need to have happen is the box should be the width of its' containing parents' VisibleWidth. Meaning, if the Window itself is 1024x768, the TextBox's MaxWidth should be 1024 and any text thereafter would automatically wrap, but if the Window grows to 1280x1024 the box should now be 1280 and the text wrap accordingly. I tried this scenario with this binding expression, but no luck:
MaxWidth="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}, Path=ActualWidth}"
The Window size itself isn't growing so if I could get the Window's Width (minus a certain amount to cover the width of the tabs that are part of the TabControl) I believe that would work.
Any ideas?

Answer 1

although the view gets scrollbars
Disable the horizontal scrollView, so it will be forced to wrap. You can try to disable it on the TextBox itself, or on the wrapping Grid.
<DataTemplate x:Key="NotesTemplate">
<Grid ScrollViewer.HorizontalScrollBarVisibility="Disabled">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<TextBlock Text="Use the box below to record any general notes associated with this item." Style="{StaticResource Default}" />
<TextBox TextWrapping="Wrap" AcceptsReturn="True" VerticalScrollBarVisibility="Auto" Grid.Row="1" Margin="20" Text="{Binding Notes, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
</DataTemplate>