WPF Binding in DataGridColumnHeader DataTemplate - wpf

Question

So, this is an extension to the following question: Style DataGridColumnHeader with Styles in WPF
In short, I'm trying to put filters in my DataGridColumnHeaders by templating the column headers with a combobox. So the difference with the other example is that I'm using ComboBoxes instead.
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="300" Width="300" Loaded="Window_Loaded">
<Window.Resources>
<DataTemplate x:Key="MySpecialHeaderTemplate">
<ComboBox ItemsSource="{Binding Codes}" />
</DataTemplate>
</Window.Resources>
<Grid>
<DataGrid>
<DataGrid.Columns>
<DataGridTextColumn
Binding="{Binding Id}" />
<DataGridTextColumn HeaderTemplate="{StaticResource MySpecialHeaderTemplate}"
Binding="{Binding Name}" />
<DataGridTextColumn HeaderTemplate="{StaticResource MySpecialHeaderTemplate}"
Binding="{Binding Age}" />
</DataGrid.Columns>
</DataGrid>
</Grid>
My question pertains to binding the ComboBox to some values. I'm currently having issues with binding the ItemsSource to a property in my ViewModel as shown above, but I can't get it to work. My second question would be how would I alter the code so that I could bind to different values per column??

Answer 1

The DataGridColumnHeaders doesn't inherit the DataContext so they have nothing to bind against. Use RelativeSource to find the parent DataGrid in the binding instead and point to DataContext.Codes
<DataTemplate x:Key="MySpecialHeaderTemplate">
<ComboBox ItemsSource="{Binding RelativeSource={RelativeSource AncestorType={x:Type DataGrid}},
Path=DataContext.Codes}" />
</DataTemplate>