Binding to elements in WPF GridViewHeader doesn't work - wpf

Question

I'm trying to create a custom header for a ListView / GridView where the user can easily filter items using Text inputs:
I've created DependencyProperties on the UserControl's code-behind and are binding the Xaml datacontext to itself (name=root). The binding i'm having trouble with is the TextBox inside the Header - it simply doesn't work. If i set a 'ModelVariantId' to "Whatever" it doesn't show and likewize i don't get any PropertyChanged events when writing in it..
I've found -some- similar sounding questions on the internet but nothing exactly matching.
<ListView ItemsSource="{Binding ElementName=root, Path=CombinedCarModels}">
<ListView.View>
<GridView>
<GridViewColumn Width="120" DisplayMemberBinding="{Binding ModelVariantId}">
<GridViewColumn.Header>
<GridViewColumnHeader HorizontalContentAlignment="Stretch">
<StackPanel>
<Label>ModelVariantId</Label>
<TextBox Text="{Binding ElementName=root,
Path=CarModelFilter.ModelVariantId, Mode=TwoWay}" />
</StackPanel>
</GridViewColumnHeader>
</GridViewColumn.Header>
</GridViewColumn>
</GridView>
</ListView.View>
</ListView>

Answer 1

If you define a HeaderTemplate, this binding should work:
Text="{Binding RelativeSource={RelativeSource AncestorType=UserControl},
Path=CarModelFilter.ModelVariantId, Mode=TwoWay}"
XAML:
<GridViewColumn.HeaderTemplate>
<DataTemplate>
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Label Grid.Row="0" HorizontalAlignment="Stretch">ModelVariantId</Label>
<TextBox Grid.Row="1" HorizontalAlignment="Stretch"
Text="{Binding ElementName=root, Path=CarModelFilter.ModelVariantId, Mode=TwoWay}" />
</Grid>
</DataTemplate>
</GridViewColumn.HeaderTemplate>
There is no element named "root" in the same naming scope as the header, but you should be able to bind to a parent element in the visual tree using the RelativeSource property.
This assumes that the parent UserControl has a CarModelFilter property.