Bjorn Kuiper

Hi,

I want to share this great post from Anoop that shows a easy way to add a notification system to dependency properties of a given element. It creates and attaches a new property to the existing property and let’s you specify the PropertyChangedCallback eventhandler.

There are different examples on the internet, but i like how Anoop created a generic method with access to the callback event handler.

Here is the main part of the code:

        /// Listen for change of the dependency property
        public void RegisterForNotification(string propertyName, FrameworkElement element, PropertyChangedCallback callback)
        {
            //Bind to a depedency property
            Binding b = new Binding(propertyName) { Source = element };
            var prop = System.Windows.DependencyProperty.RegisterAttached(
                "ListenAttached"+propertyName,
                typeof(object),
                typeof(UserControl),
                new System.Windows.PropertyMetadata(callback));

            element.SetBinding(prop, b);
        }

And here is an example on how to use it:

//Shows a message box when the text of the Textbox changes.
RegisterForNotification
	("Text", this.txtMain,(d,e)=>MessageBox.Show("Text changed"));

Read Anoop’s complete article for more information!

update (07/28/2011):
here is small update of the code so it also works with other objects instead of just FrameworkElements

        private void RegisterForNotification(string propertyName, object source, PropertyChangedCallback callback)
        {
            Binding b = new Binding(propertyName);
            b.Source = source;

            DependencyProperty prop = System.Windows.DependencyProperty.RegisterAttached(
                "ListenAttached" + propertyName,
                typeof(object),
                this.GetType(),
                new System.Windows.PropertyMetadata(callback));

            BindingOperations.SetBinding(this, prop, b);
        }