If I have a MethodInfo on a closed generic Type is there an easy way to switch those types?

Question

Let\'s say that I have the methodInfo for something like Nullable.HasValue. Is there anyway to convert it to Nullable.HasValue

Answer 1

Solved it. But the big question is this a safe way to do it? Is there something I could be doing wrong here?

    public static MethodInfo Convert(this MethodInfo method,params Type[] DeclaringTypeArguments)
    {
        var baseType = method.DeclaringType.GetGenericTypeDefinition().MakeGenericType(DeclaringTypeArguments);
        return MethodInfo.GetMethodFromHandle(method.MethodHandle, baseType.TypeHandle) as MethodInfo;
    }
    public static void Main(String[] args)
    {
        List<Type> list = new List<Type>(); 
        Action<Type> action  = list.Add;
        Console.WriteLine(action.Method.Convert(typeof(string)));
        Console.Read();
    }

Answer 2

You can do it in one line with MethodBase.GetMethodFromHandle but in order to use this method you'll have to pass typeof(List<string>) not just typeof(string).

var methodinfo = typeof(List<int>).GetMethod("Add");
var methodinfo2 = MethodBase.GetMethodFromHandle(methodinfo.MethodHandle,
                                                 typeof (List<string>).TypeHandle);

Console.WriteLine(methodinfo);
Console.WriteLine(methodinfo2);

This link includes the above sample and an exlpanation of why ResolveMethod doesn't work.

https://www.re-motion.org/blogs/mix/archive/2009/08/12/trying-to-resolve-a-method-in-a-closed-generic-type.aspx

Answer 3

You can do it easily with a little more reflection. You can't do it magically without reflection.

    static void Main(string[] args)
    {
        PropertyInfo intHasValue = typeof (int?).GetProperty("HasValue");
        PropertyInfo boolHasValue = ChangeGenericType(intHasValue, typeof (bool));
    }

    public static PropertyInfo ChangeGenericType(PropertyInfo property, Type targetType)
    {
        Type constructed = property.DeclaringType;
        Type generic = constructed.GetGenericTypeDefinition();
        Type targetConstructed = generic.MakeGenericType(new[] {targetType});
        return targetConstructed.GetProperty(property.Name);
    }

Of course this is pretty specific to only work for generic types with a single type parameter but it could be generalized to do more if needed.

Answer 4

You have to reflect again because the methods are different. While the only difference for HasValue is the MethodInfo.DeclaringType, the difference in the Value property is the MethodInfo.ReturnType.