WPF:为什么没有在逻辑子上引发DataContextChanged？

public static readonly DependencyProperty DataContextProperty = DependencyProperty.Register("DataContext", typeof(object), typeof(MyControl), new FrameworkPropertyMetadata(null, OnDataContextChanged));

public object DataContext
{
    get { return GetValue(DataContextProperty); }
    set { SetValue(DataContextProperty, value); }
}

private static void OnDataContextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    MyControl control = (MyControl)d;
    control.RaiseEvent(new RoutedEventArgs(DataContextChangedEvent));
}

public static readonly RoutedEvent DataContextChangedEvent = EventManager.RegisterRoutedEvent("DataContextChanged", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(MyControl));

public event RoutedEventHandler DataContextChanged
{
    add { AddHandler(DataContextChangedEvent, value); }
    remove { RemoveHandler(DataContextChangedEvent, value); }
}