DependencyProperty PropertyChangedCallback wiring

Question

I have a user control with a UniformGrid that has a number of Buttons. I want to assign the same handler to each Button's Click event. So, I added the following to the User Control:

    public RoutedEventHandler GridButtonClickHandler
    {
        get { return ( RoutedEventHandler ) GetValue ( GridButtonClickHandlerProperty ); }
        set { SetValue ( GridButtonClickHandlerProperty, value ); }
    }

    public static readonly DependencyProperty GridButtonClickHandlerProperty =
        DependencyProperty.Register ( "GridButtonClickHandler", typeof ( RoutedEventHandler ), typeof ( UniformGrid ),
            new PropertyMetadata ( GridButtonClickPropertyChanged ) );

    private static void GridButtonClickPropertyChanged ( DependencyObject o, DependencyPropertyChangedEventArgs e )
    {
        ( ( UniformGrid ) o ).Children.OfType<Button> ( ).ToList ( ).ForEach ( b => b.Click += ( RoutedEventHandler ) e.NewValue );
    }

Then, somewhere where there is a reference to the User Control (numpad in this example), I have this:

numpad.GridButtonClickHandler += btn_clicked;

I have breakpoints at the GridButtonClickHandler set and the GridButtonClickPropertyChanged method; the first hits when the assignment happens, but the second never hits.

See what I am doing wrong?

Answer 1

You have registered your dependency propery on the UniformGrid to set a handler to it you need an UniformGrid instance and the following code:

uniformGrid.SetValue(MyUserControl.GridButtonClickHandlerProperty, new RoutedEventHandler(btn_clicked));

If it was not your goal and would like use it : numpad.GridButtonClickHandler += btn_clicked; where numpad is your usercontrol. Then the owner type should be your user control during the registration:

public static readonly DependencyProperty GridButtonClickHandlerProperty =
        DependencyProperty.Register ( "GridButtonClickHandler", 
        typeof ( RoutedEventHandler ), 
        typeof ( MyUserControl),
            new PropertyMetadata ( GridButtonClickPropertyChanged ) );

Answer 2

You need a routed event, not a dependency property...

public static readonly RoutedEvent GridButtonClickEvent = EventManager.RegisterRoutedEvent("GridButtonClick", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(MyUserControl));

public event RoutedEventHandler GridButtonClick
{
    add { AddHandler(GridButtonClickEvent, value); }
    remove { RemoveHandler(GridButtonClickEvent, value); }
}

And when a button is clicked, raise the event:

private void GridButton_Click(object sender, RoutedEventArgs e)
{
    RaiseEvent(new RoutedEventArgs(GridButtonClickEvent, this));
}