public class People : DependencyObject
    {
        public static readonly DependencyProperty NameProperty =
            DependencyProperty.Register("Name", typeof (string), typeof (People), new PropertyMetadata(default(string)));

        public string Name
        {
            get { return (string) GetValue(NameProperty); }
            set { SetValue(NameProperty, value); }
        }
    }

//.........
        private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
        {
            var people = new People {Name = "zhang san"};

            var descriptor =  DependencyPropertyDescriptor.FromProperty(People.NameProperty, typeof (People));
            descriptor.AddValueChanged(people, (o, args) => MessageBox.Show("name changed to " + people.Name));

            people.Name = "Li si";
        }