Bind to parent datacontext (out of itemsource)

Question

In my Windows Phone 8 app I have list of items. I have defined ItemTemplate for list items.

I want to display in each of these items one value from view model, not from the list item itself. How should I set up the binding from list item to viewmodel.

My data template is like this:

<DataTemplate x:Key="template">
    <StackPanel>
        <TextBlock Text="{Binding Name}"/> <!-- From list item -->
        <TextBlock Text="{Binding MyViewModel.Country ?? }"/> <!-- From view model -->
    </StackPanel>  
</DataTemplate>

So how to bind Country property to view model, not list item (in item source).

Answer 1

Since you tagged your question with WPF, I can tell you the way of doing it in WPF, you can validate if that can be reused in Windows phone 8 apps.

First, you can give x:Name to root element to which ViewModel is bind to. Say it's window, set x:Name on it and bind using ElementName.

<Window x:Name="myWindow">
  ...
  <DataTemplate x:Key="template">
    <StackPanel>
        <TextBlock Text="{Binding Name}"/> <!-- From list item -->
        <TextBlock Text="{Binding DataContext.MyViewModel.Country,
                            ElementName=myWindow }"/> <!-- From view model -->
    </StackPanel>  
</DataTemplate>
</Window>

---

Second, you can try using RelativeSource to travel Visual tree and get root element DataContext.

<DataTemplate x:Key="template">
    <StackPanel>
        <TextBlock Text="{Binding Name}"/> <!-- From list item -->
        <TextBlock Text="{Binding DataContext.MyViewModel.Country,
                           RelativeSource={RelativeSource Mode=FindAncestor, 
                                                   AncestorType=Window} }"/>
                         <!-- From view model -->
    </StackPanel>  
</DataTemplate>

---

Moreove, if ListBox is inheriting DataContext from root element (i.e. you haven't explicitly set DataContext on ListBox). You can use both approaches on ListBox as well in place of Window.

Note - As mentioned here, FindAncestor is not defined for Windows phone 8 but element name does work. So, try using first approach and it should work for you.