WPF-Demo/WpfSample/AttachedProperty.cs

using System.Windows;
using System.Windows.Controls;

namespace WpfSample {
    static class PropADemo {
        public static string GetText(DependencyObject obj) {
            return (string)obj.GetValue(TextProperty);
        }

        public static void SetText(DependencyObject obj, string value) {
            obj.SetValue(TextProperty, value);
        }

        public static readonly DependencyProperty TextProperty =
            DependencyProperty.RegisterAttached("Text", typeof(string), typeof(PropADemo),
                new PropertyMetadata(string.Empty, OnTextChanged));

        private static void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
            if (d is Control control) {

            }
        }

    }
}