Question

this is the Code behind of user control

 public delegate void YardSelectionChangedDelegate();
 public event YardSelectionChangedDelegate YardSelectionChanged;
 public static readonly DependencyProperty SelectedYardIdProperty =
     DependencyProperty.Register(
         "SelectedYardId",
         typeof(long),
         typeof(YardSelectorUserControl),
         new UIPropertyMetadata(null));

And this is the Property:

public long SelectedYardId
{
    get { return (long)GetValue(SelectedYardIdProperty); }
    set { SetValue(SelectedYardIdProperty, value); }
}

And this is the Binding in the parent window:

SelectedYardId="{Binding  Path=YardId,UpdateSourceTrigger=PropertyChanged}" 

The problem is that the Set of the property never work and cursor never reach the Set body.
thanks indeed.

Answer 1

That is because binding engine doesn’t use your set or get accessors for setting or getting a property. It uses SetValue and GetValue of the DependencyObject directly. In order to trigger an event while changing a dependency property you need to define a callback delegate while registering your dependency property like this:

public static readonly DependencyProperty SelectedYardIdProperty =
    DependencyProperty.Register(
        "SelectedYardId",
        typeof(long),
        typeof(YardSelectorUserControl),
        new UIPropertyMetadata(OnSelectedYardIdChanged));

public static void OnSelectedYardIdChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
     // Action 
}