Binding DataContext to ValidationRule

Question

I have a custom ValidationRule that requires access to the ViewModel in order to validate a supplied value in conjunction with other properties of the ViewModel. I previously tr

Answer 1

I use a different approch. Use Freezable objects to make your bindings

As for the Binding proxy, here you go: public class BindingProxy : Freezable {

    public static readonly DependencyProperty SourceProperty;

    /// 

    /// The target property
    /// 
    public static readonly DependencyProperty TargetProperty;


    /// 

    /// Initializes static members of the  class.
    /// 
    static BindingProxy()
    {
        var sourceMetadata = new FrameworkPropertyMetadata(
        delegate(DependencyObject p, DependencyPropertyChangedEventArgs args)
        {
            if (null != BindingOperations.GetBinding(p, TargetProperty))
            {
                (p as BindingProxy).Target = args.NewValue;
            }
        });

        sourceMetadata.BindsTwoWayByDefault = false;
        sourceMetadata.DefaultUpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;

        SourceProperty = DependencyProperty.Register(
            "Source",
            typeof(object),
            typeof(BindingProxy),
            sourceMetadata);

        var targetMetadata = new FrameworkPropertyMetadata(
            delegate(DependencyObject p, DependencyPropertyChangedEventArgs args)
            {
                ValueSource source = DependencyPropertyHelper.GetValueSource(p, args.Property);
                if (source.BaseValueSource != BaseValueSource.Local)
                {
                    var proxy = p as BindingProxy;
                    object expected = proxy.Source;
                    if (!object.ReferenceEquals(args.NewValue, expected))
                    {
                        Dispatcher.CurrentDispatcher.BeginInvoke(
                            DispatcherPriority.DataBind, 
                            new Action(() =>
                            {
                                proxy.Target = proxy.Source;
                            }));
                    }
                }
            });

        targetMetadata.BindsTwoWayByDefault = true;
        targetMetadata.DefaultUpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
        TargetProperty = DependencyProperty.Register(
            "Target",
            typeof(object),
            typeof(BindingProxy),
            targetMetadata);
    }

    /// 

    /// Gets or sets the source.
    /// 
    /// 
    /// The source.
    /// 
    public object Source
    {
        get
        {
            return this.GetValue(SourceProperty);
        }

        set
        {
            this.SetValue(SourceProperty, value);
        }
    }

    /// 

    /// Gets or sets the target.
    /// 
    /// 
    /// The target.
    /// 
    public object Target
    {
        get
        {
            return this.GetValue(TargetProperty);
        }

        set
        {
            this.SetValue(TargetProperty, value);
        }
    }

    /// 

    /// When implemented in a derived class, creates a new instance of the  derived class.
    /// 
    /// 
    /// The new instance.
    /// 
    protected override Freezable CreateInstanceCore()
    {
        return new BindingProxy();
    }
}

}