Attached Properties as XAML Elements

Question

I've got a class of attached properties:

public static class XamlProps
{
    #region Attached Properties

    private static readonly DependencyProperty FooProperty = DependencyProperty.RegisterAttached(
        "Foo",
        typeof(string),
        typeof(XamlProps),
        null);

    public static void SetFoo(DependencyObject obj, string action)
    {
        obj.SetValue(FooProperty, action);
    }
}

And I use these properties in my XAML:

<Border me:XamlProps.Foo="Foo to the Bar">

But now I want a larger value in this property, so I'd like to use it as an element:

<Border>
    <me:XamlProps.Foo>Foo to the Bar</me:XamlProps.Foo>
</Border>

But now Silverlight doesn't call SetFoo() anymore. How do I get this to work?

On Windows Phone 7 if it matters.

Answer 1

You'll need to specify the type if you use that syntax:

<Border>
    <me:XamlProps.Foo>
        <sys:String>Foo to the Bar</sys:String>
    </me:XamlProps.Foo>
</Border>

Where the sys namespace maps to System. You also need to define GetFoo ...

Probably a copy-paste typo, but in the registration

typeof(XamlActions)

should be

typeof(XamlProps)

Answer 2

You should never rely on the SetFoo being called. Anything can simply call SetValue(FooProperty, "blah") and bypass it.

You should define a PropertyChangedCallback in your DependencyProperty.Register call to be notified of changes.