How to call a generic extension method with reflection?

Question

I wrote the extension method GenericExtension. Now I want to call the extension method Extension. But the value of methodInfo is always null.

public static class MyClass
{
    public static void GenericExtension<T>(this Form a, string b) where T : Form
    {
        // code...
    }

    public static void Extension(this Form a, string b, Type c)
    {
        MethodInfo methodInfo = typeof(Form).GetMethod("GenericExtension", new[] { typeof(string) });
        MethodInfo methodInfoGeneric = methodInfo.MakeGenericMethod(new[] { c });
        methodInfoGeneric.Invoke(a, new object[] { a, b });
    }

    private static void Main(string[] args)
    {
        new Form().Extension("", typeof (int));
    }
}

Whats wrong?

Answer 1

The extension method isn't attached to the type Form, it's attached to the type MyClass, so grab it off that type:

MethodInfo methodInfo = typeof(MyClass).GetMethod("GenericExtension",
    new[] { typeof(Form), typeof(string) });