Like this:

We’ve just been doing some multi-touch WPF work. Well, when I say ‘we’ I really mean everyone else apart from me as it got into what I consider to be serious math of which I have very little (zero) knowledge. Anyway, I digress.

One of the things that has bugged me with WPF are the Dependency Properties, or at least the ugliness of them. An example is

public static readonly DependencyProperty CameraPostionProperty =
    DependencyProperty.Register("CameraPosition", typeof(Point3D), typeof(WorldViewModel));

What bug’s me most is the Register method. I don’t like the magic string which can get lost during a refactor and it would be far too easy to get the order of the type parameters the wrong way round. Just a misspelling of the string is enough for it to not work (which happens far more often than it should).

A much preferable syntax would be the following:

public static readonly DependencyProperty CameraLookDirectionProperty =
    DependencyPropertyHelper<WorldViewModel>.Register(x => x.CameraLookDirection);

With this syntax theirs no magic strings and no types to get mixed up.

This syntax is achieved with the code below:

public static class DependencyPropertyHelper<T>
{
    public static DependencyProperty Register<TR>(Expression<Func<T, TR>> action)
    {
        var member = (MemberExpression)action.Body;
        return DependencyProperty.Register(member.Member.Name, typeof(TR), typeof(T));
    }
}

Now we are taking the string from the member name itself and the order of the types is picked up correctly.

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