Attached Property with custom class list. Bind Class Property to TextBox?

Hello,

i have an Attached Property with a list of a custom class. A Property of the custom class is bound to a textbox text. 

I want to get an update or any function called when i enter text in the textbox or the bound value is changing.

It looks to me that the binding is lost.

Do you have any suggestions?

CustomClass:

   public class ComparsionCondition : DependencyObject
    {
        public static readonly DependencyProperty BindingValueProperty =
             DependencyProperty.Register("BindingValue", typeof(string),
             typeof(ComparsionCondition), new PropertyMetadata("bindval"));

        public string BindingValue 
        {
            get
            {
                return (string)GetValue(BindingValueProperty);
            }
            set
            {
                SetValue(BindingValueProperty, value);
            }
        }
    }

Behavior:

 public static class ComparsionBehavior 
    {
        #region ComparsionConditions
        public static TrulyObservableCollection<ComparsionCondition> GetComparsionConditions(DependencyObject frameworkElement)
        {
            return (TrulyObservableCollection<ComparsionCondition>)frameworkElement.GetValue(ComparsionConditionsProperty);
        }

        public static void SetComparsionConditions(DependencyObject frameworkElement, TrulyObservableCollection<ComparsionCondition> value) 
        {
            frameworkElement.SetValue(ComparsionConditionsProperty, value);
        }

        public static readonly DependencyProperty ComparsionConditionsProperty = DependencyProperty.RegisterAttached(
            "ComparsionConditions", typeof(TrulyObservableCollection<ComparsionCondition>), typeof(ComparsionBehavior), new UIPropertyMetadata(new TrulyObservableCollection<ComparsionCondition>(), OnComparsionConditionsChanged));

        static void OnComparsionConditionsChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e) 
        {
            HandlePropertyChanged(sender);
        }
        #endregion
    }

XAML usage:

<TextBox Text="85" x:Name="tb_value"></TextBox><Border><Behavior:ComparsionBehavior.ComparsionConditions><Behavior:ComparsionCondition BindingValue="{Binding Path=Text, ElementName=tb_value}"></Behavior:ComparsionCondition></Behavior:ComparsionBehavior.ComparsionConditions></Border>

Best regards,

Simon

tu es, oder lass es