Limit attached dependency property in wpf

Question

I want to attach a dependency property to specific controls only.

If that is just one type, I can do this:

public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.RegisterAttached("MyProperty", typeof(object), typeof(ThisStaticWrapperClass));

public static object GetMyProperty(MyControl control)
{
    if (control == null) { throw new ArgumentNullException("control"); }

    return control.GetValue(MyPropertyProperty);
}

public static void SetMyProperty(MyControl control, object value)
{
    if (control == null) { throw new ArgumentNullException("control"); }

    control.SetValue(MyPropertyProperty, value);
}

(So: limit the Control type in the Get/Set-Methods)

But now I want to allow that property to get attached on a different type of Control , too.
You'd try to add an overload for both methods with that new type, but that fails to compile because of an "Unknown build error, Ambiguous match found."

So how can I limit my DependencyProperty to a selection of Control s?
(Note: In my specific case I need it for TextBox and ComboBox )

Answer 1

Ambiguous match found.

...is normally thrown by GetMethod if there are multiple overloads and no type-signature has been specified (MSDN: More than one method is found with the specified name. ). Basically the WPF-engine is only looking for one such method.

Why not check the type in the method body and throw an InvalidOperationException if it's not allowed?

---

Note however that those CLR-Wrappers should not include any code beside the setting and getting, if the propery is set in XAML they will be disregarded , try throwing an exception in the setter, it will not come up if you only use XAML to set the value.

Use a callback instead:

public static readonly DependencyProperty MyPropertyProperty =
    DependencyProperty.RegisterAttached
        (
            "MyProperty",
            typeof(object),
            typeof(ThisStaticWrapperClass),
            new UIPropertyMetadata(null, MyPropertyChanged) // <- This
        );

public static void MyPropertyChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
{
    if (o is TextBox == false && o is ComboBox == false)
    {
        throw new InvalidOperationException("This property may only be set on TextBoxes and ComboBoxes.");
    }
}