Is it possible to write new attached property like Validation.Errors, say MyValidation.XYZ

Alexander Landa 0 Reputation points


I would like to use some set of my own different attached properties not defined in Validation.cs.

Actually I've tried all known possible ways including AddValueChanged for existing public Validation.<DependencyProperty>, but no have no luck - I get only a default value of new property and has no chance to get an actualization event fired.

Thank you for assistance.

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  1. Hui Liu-MSFT 37,351 Reputation points Microsoft Vendor

    Hi,@Alexander Landa. Welcome to Microsoft Q&A. It is possible to create your own attached properties in WPF, similar to Validation.Errors, for various purposes such as custom validation, behavior addition, or data binding facilitation.

    Here's an example of create a custom attached property MyValidation.XYZ:

        <TextBox Width="100" Height="60" Text="{Binding MyValue}" local:MyValidation.XYZ="{Binding MyValue}" />


    public partial class MainWindow : Window,INotifyPropertyChanged
        public MainWindow()
            DataContext = this;
        private string myValue;
        public string MyValue
            get { return myValue; }
            set { myValue = value; OnPropertyChanged(); }
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string name = null)
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
    public static class MyValidation
        public static readonly DependencyProperty XYZProperty =
            DependencyProperty.RegisterAttached("XYZ", typeof(string), typeof(MyValidation),
                new PropertyMetadata(null, OnXYZPropertyChanged));
        public static string GetXYZ(DependencyObject obj)
            return (string)obj.GetValue(XYZProperty);
        public static void SetXYZ(DependencyObject obj, string value)
            obj.SetValue(XYZProperty, value);
        private static void OnXYZPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
            // This method will be called whenever the value of XYZ property changes
            // You can perform any necessary actions here
            string newValue = (string)e.NewValue;
            string oldValue = (string)e.OldValue;
            // Example: Logging the change
            System.Diagnostics.Debug.WriteLine($"XYZ property changed from '{oldValue}' to '{newValue}'");

    The result:

    When MyValue changes, a meesage is displayed in the output window.

    XYZ property changed from '' to 'FFF' XYZ property changed from 'FFF' to 'DDD'

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