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

  public class BindingProxy : Freezable
    {
            

        
            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);
            }
          
public static readonly DependencyProperty SourceProperty;   
            public static readonly DependencyProperty TargetProperty;
       
            public object Source
            {
                get
                {
                    return this.GetValue(SourceProperty);
                }

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

           
            public object Target
            {
                get
                {
                    return this.GetValue(TargetProperty);
                }

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

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

sHould This have the problem of binding the value too late after the application started. I use Blend Interactions to resolve the problem after the window loads