Question

For my own personal edification–is there any way to do this? I’m implementing an Imageable class that provides a ToWmf() function that outputs the WPF object to a vector graphic. But this only makes sense for WPF Visual types, and so one of the components of the imaging operation requires a parameter with type Visual, which I would intend to be this.

I’ve found all kinds of examples of C# parameter constraints but no examples of constraining the inheriting class type. For the time being I’m using a static ImagingUtil.ToWmf() class, but is this just a flat-out No answer or is there another way?

Answer 1

The question implies that the Imageable object would also be a Visual at the same time (otherwise how are you going to pass this to something that needs a Visual?).

This is not possible unless one of the two types inherits from the other, and since Visual is not under your control then Imageable must be a descendant of Visual. In which case there is no problem at all.

In all likelihood what you want to be doing is defining an IImageable interface and then implementing an extension method that looks like this:

public static void ToWmf<T>(this T imageable) where T : Visual, IImageable
{
    // ....
}

This way any (and only a) user-defined class that derives from Visual and at the same time implements IImageable can be processed by ToWmf.