Question

I have a custom UserControl:

public partial class CustomCtrl : UserControl
{
    public CustomCtrl()
    {
        InitializeComponent();
    }

    public string Prova
    {
        get { return (string)GetValue(ProvaProperty); }
        set 
        {
            SetValue(ProvaProperty, value); 
        }
    }

    public static readonly DependencyProperty ProvaProperty =
        DependencyProperty.Register("Prova", typeof(string), typeof(CustomCtrl));

}

I do this simple binding:

CustomCtrl c = new CustomCtrl();
TextBlock t = new TextBlock();
c.SetBinding(CustomCtrl.ProvaProperty, new Binding("Text") { Source = t });
t.Text = "new string";

Now c.Prova is “new string“, but how can I catch in my CustomControl class the event informing me that Prova has changed?

Answer 1

Something like this (this will catch changes on all instances of CustomCtrl):

public static readonly DependencyProperty ProvaProperty =
    DependencyProperty.Register(
    "Prova",
    typeof(string),
    typeof(CustomCtrl),
    new PropertyMetadata( new PropertyChangedCallback(OnValueChanged) )
);

private static void OnValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    // This is called whenever the Prova property has been changed.
}

If “clients” of your CustomCtrl wanted to catch a change to that property for a specific instance then they could use:

CustomCtrl instanceofsomecustomctrl = .......

DependencyPropertyDescriptor descr = 
                  DependencyPropertyDescriptor.FromProperty(CustomCtrl.ProvaProperty, typeof(CustomCtrl));

if (descr != null)
{
    descr.AddValueChanged(instanceofsomecustomctrl, delegate
        {
            // do something because property changed...
        });
}