绑定祖先不工作WPF

public class BindableAncestor : DependencyObject
{
    public static readonly DependencyProperty AncestorProperty =
        DependencyProperty.Register("Ancestor", typeof(object), typeof(BindableAncestor),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits, OnAncestorPropertyChanged));

    public object Ancestor
    {
        get { return (object)GetValue(AncestorProperty); }
        set { SetValue(AncestorProperty, value); }
    }

    private static void OnAncestorPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        BindableAncestor ancestor = sender as BindableAncestor;
        if (ancestor != null)
        {
            ancestor.Ancestor = e.NewValue;
        }
    }
}

public class BindableAncestor : DependencyObject
{
    public static readonly DependencyProperty AncestorProperty =
        DependencyProperty.Register("Ancestor", typeof(object), typeof(BindableAncestor),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits, OnAncestorPropertyChanged));

    public object Ancestor
    {
        get { return (object)GetValue(AncestorProperty); }
        set { SetValue(AncestorProperty, value); }
    }

    private static void OnAncestorPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        BindableAncestor ancestor = sender as BindableAncestor;
        if (ancestor != null)
        {
            ancestor.Ancestor = e.NewValue;
            WeakEventManager.AddListener(ancestor.Ancestor, new PropertyChangedEventHandler(OnAncestorPropertyChanged));
        }
    }

    private void OnAncestorPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.Property == AncestorProperty)
        {
            WeakEventManager.RemoveListener(sender as object, new PropertyChangedEventHandler(OnAncestorPropertyChanged));
        }
    }
}

public class BindableAncestor : DependencyObject, INotifyPropertyChanged
{
    public static readonly DependencyProperty AncestorProperty =
        DependencyProperty.Register("Ancestor", typeof(object), typeof(BindableAncestor),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.Inherits, OnAncestorPropertyChanged));

    public object Ancestor
    {
        get { return (object)GetValue(AncestorProperty); }
        set { SetValue(AncestorProperty, value); }
    }

    private static void OnAncestorPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        BindableAncestor ancestor = sender as BindableAncestor;
        if (ancestor != null)
        {
            ancestor.Ancestor = e.NewValue;
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(sender, new PropertyChangedEventArgs("Ancestor"));
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}