WPF - MVVM - Proxy Binding

Here the purpose is to be able to bind a Command on a Button which is under 2 levels of ItemsControl without using the “Ancestor” stuff.

So the classic way of doing this:

the following should work :

<TextBlock Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.Client.Name}" />

But we can do something better and more readable.

Create a new helper class:

public class DataContextProxy : Freezable
{
   #region Overrides of Freezable

   protected override Freezable CreateInstanceCore()
   {
      return new DataContextProxy();
   }

   #endregion

   public object DataSource
   {
      get { return (object)GetValue(DataProperty); }
      set { SetValue(DataProperty, value); }
   }

   public static readonly DependencyProperty DataProperty = DependencyProperty.Register("DataSource", typeof(object), typeof(DataContextProxy), new UIPropertyMetadata(null));
}

Then in the View, add a resource to this new helper class:

<UserControl.Resources>
   <helpers:DataContextProxy x:Key="DataContextProxy" DataSource="{Binding}"/>
</UserControl.Resources>

Then in your Grid:

<ItemsControl Margin="5" ItemsSource="{Binding ClientRows}">
 <ItemsControl.ItemTemplate>
 <DataTemplate>
 <StackPanel Orientation="Horizontal">

<!--CLIENT-->
 <Border BorderBrush="LightGray" BorderThickness="1">
 <StackPanel Orientation="Horizontal" Width="150">

<!--CLIENT NAME-->
 <TextBlock TextAlignment="Center" HorizontalAlignment="Center" VerticalAlignment="Center" Width="100"
 Text="{Binding Client.Name}" />

<!--BUTTONS-->
 <Button Height="23" Content="Delete Client"
 Command="{Binding Source={StaticResource DataContextProxy}, Path=DataSource.DeleteClientCommand}"
 CommandParameter="{Binding}"
 Visibility="{Binding IsDeleteVisible}" />
...

So here we don’t need anymore to know at which level of the binding we are.

We just call the Proxy (DataContextProxy) to set the binding.

WPF – MVVM – Proxy Binding

Related posts: