Binding a Resource to a View Model

Question

How do you bind data from the view model into an object in the resources of the user control? Here is a very abstract example:

<UserControl ... 
             xmlns:local="clr-namespace:My.Local.Namespace"
             Name="userControl">
    <UserControl.Resources>
        <local:GroupingProvider x:Key="groupingProvider" GroupValue="{Binding ???}" />
    </UserControl.Resources>

    <Grid>
        <local:GroupingConsumer Name="groupingConsumer1" Provider={StaticResource groupingProvider"} />
        <local:GroupingConsumer Name="groupingConsumer2" Provider={StaticResource groupingProvider"} />
    </Grid>
</UserControl>

How do I bind GroupValue to a property in the view model behind this view. I've tried the following:

<local:GroupingProvider x:Key="groupingProvider" GroupValue="{Binding ElementName=userControl, Path=DataContext.Property}"/>

But this doesn't work.

Edit:

GroupProvider extends DependencyObject and GroupValue is the name of a DependencyProperty. I'm getting the following error:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=DataContext.Property; DataItem=null; target element is 'GroupingProvider' (HashCode=47478197); target property is 'GroupValue' (type 'TimeSpan')

This seems to suggest that it cannot find userControl.

More Edit:

Nobody has an answer to my question? Is there not a way to do this?

Answer 1

I know its a bit late, but i had the same problem. Ricks answer is right, you need to inherit from Freezable.

The following Code gave me the same error as you got

Not working resource:

public class PrintBarcodesDocumentHelper : DependencyObject
{
    public IEnumerable<BarcodeResult> Barcodes
    {
        get { return (IEnumerable<BarcodeResult>)GetValue(BarcodesProperty); }
        set { SetValue(BarcodesProperty, value); }
    }

    public static readonly DependencyProperty BarcodesProperty =
        DependencyProperty.Register("Barcodes", typeof(IEnumerable<BarcodeResult>), typeof(PrintBarcodesDocumentHelper), new PropertyMetadata(null, HandleBarcodesChanged));

    private static void HandleBarcodesChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // Do stuff
    }
}

Xaml:

<UserControl.Resources>
    <Barcodes:PrintBarcodesDocumentHelper x:Key="docHelper" Barcodes="{Binding BarcodeResults}"/>
</UserControl.Resources>

My viewmodel is bound to the DataContext of the UserControl.

Error:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=BarcodeResults; DataItem=null; target element is 'PrintBarcodesDocumentHelper' (HashCode=55335902); target property is 'Barcodes' (type 'IEnumerable`1')

Working resource class:

public class PrintBarcodesDocumentHelper : Freezable
{
    // Same properties

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

Unfortunately i dont know why it have to be a Freezable.

Answer 2

In order to enable binding, GroupingProvider needs to be derived from Freezable or FrameworkElement or FrameworkContentElement and GroupValue needs to be a DependencyProperty.