Question

I have several DllImports with respect to user32.dll in my code and I thought them to be declared in an interface. But that gives me errors saying public, static, extern are not valid with each item.

Example interface code is as follows:

public interface IWindowsFunctions
{
   [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
   static extern int MessageBox(int hWnd, string msg, string title, uint flags);
}

Is there any specific way of using this in an interface, or is there an alternative or is it impossible with an interface?

Thanks

Answer 1

Well its already been mentioned many times now that a DLLImport is an implementation, and therefore cannot be defined on an interface, but I thought it would still be worth mentioning that normally I group by DLLImports into a “NativeMethods” class for organisation, like so:

internal static class NativeMethods
{
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern int MessageBox(int hWnd, string msg, string title, uint flags);
}

Example use:

NativeMethods.MessageBox(myWnd, "Hello World", "Hello", flags);