Access parent datacontext in listbox in Silverlight


In Silverlight 2 I'm using a usercontrol which inherits the datacontext of the page that it's embedded on. This datacontext contains question text, a question type and a collection of answers. In the user control is a listbox which is bound to the collection of answers. As shown below:

<ListBox DataContext="{Binding}" x:Name="AnswerListBox" ItemContainerStyle="{StaticResource QuestionStyle}" Grid.Row="1" Width="Auto" Grid.Column="2" ItemsSource="{Binding Path=AnswerList}" BorderBrush="{x:Null}" />       

This listbox has an associated style to display the answers in the form of radio buttons or checkboxes (which I would like to hide or show depending on the question type) as:

<Style TargetType="ListBoxItem" x:Key="QuestionStyle">
            <Setter Property="Template">
                    <ControlTemplate TargetType="ListBoxItem">                      
                        <StackPanel Background="Transparent" >
                            <RadioButton Visibility="{Binding Path=QuestionType, Converter={StaticResource QuestionTypeConverter}, ConverterParameter='RadioButtonStyle'}" Height="auto" Margin="0,0,0,10"  IsChecked="{TemplateBinding IsSelected}" IsHitTestVisible="False" Content="{Binding Path=AnswerText}">
                            <CheckBox Visibility="{Binding Path=QuestionType, Converter={StaticResource QuestionTypeConverter}, ConverterParameter='CheckBoxStyle'}" Height="auto" Margin="0,0,0,10" Content="{Binding Path=AnswerText}">

So my question is then: how do you access the parent data context in order to get the QuestionType (as this is a property on the user control datacontext itself, not a property on an AnswerItem in the AnswerList)?

Alternatively is there a better way to switch styles dynamically in the xaml based on a binding value?

Best Solution

In Silverlight 3 and higher you can use Element to Element binding and point to the controls DataContext and then some property in my example its Threshold property.

So first name your control (for example in my example its x:Name="control")

<UserControl x:Class="SomeApp.Views.MainPageView" x:Name="control" >

then inside this control in your ListBox ItemTemplate you can access parent DataContext like this:

    <ListBox ItemsSource="{Binding Path=SomeItems}" >
            <StackPanel Orientation="Horizontal">
            <TextBlock Text="{Binding ElementName=control, Path=DataContext.Threshold}"/>