Binding to DataContext outside current ItemsSource context

Question

I have a DataSet bound to the Window.DataContext; I also have a DataGrid:

<DataGrid ItemsSource={Binding Tables[Items]}>
    <DataGrid.Columns>
        <DataGridTextBoxColumn Header={Binding Path=DataContext.Tables[Names]/Test, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}} />
    </DataGrid.Columns>
</DataGrid>

Basically, I'm trying to bind the Header of that column to DataTable "Names", Column "Test", first row.

However, I can't get it right. Note that I can bind it fine outside the DataGrid. The Grid's ItemsSource changes the data context and I don't know how to refer outside to the original DataContext.

It seems that the binding succeeds; but the problem is that the current item (first row) of the Tables[Names] in the Window.DataContext got lost.

If I make the DataSet static and access it via {x:Static local:dataset} then things work fine. But I can't use static datasets because there will be multiple instances (multi-user).

Can anyone please point me in the right direction?

Answer 1

I'm pretty sure you could do what you're trying to do by using RelativeSource binding.

<DataGrid ItemsSource="{Binding StringCollection}" 
          AutoGenerateColumns="False">
  <DataGrid.Columns>
    <DataGridTextColumn Binding="{Binding}" />
    <DataGridTextColumn Binding="{
                          Binding RelativeSource={
                            RelativeSource FindAncestor, 
                            AncestorType={x:Type Window}},
                          Path=DataContext.SomethingOutsideDataContext}" />
  </DataGrid.Columns>
</DataGrid>

I made a quick example at: http://bitbucket.org/claus/wpf-bindingoutsidedatacontext

It allows you to bind to the parent Window, which in my case has the viewmodel as datacontext (with the SomethingOutsideDataContext property on it).

You should be aware though, this will only work with WPF and not Silverlight - the 'FindAncestor, AncestorType' stuff has not been implemented in Silverlight yet... I'm not sure if there's another method, besides using static resources.