c# - How can I fix this up to do generic conversion to Nullable<T>?

Question

I currently use this handy conversion extension method to do conversions between types:

    public static T To<T>(this IConvertible obj)
    {
        return (T)Convert.ChangeType(obj, typeof(T));
    }

However, it doesn't like converting valid values to Nullable, for example, this fails:

    "1".To<int?>();

Obviously, 1 is easily converted to an (int?), but it gets the error:

    Invalid cast from 'System.String' to 'System.Nullable`1[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]'.

This is an obviously simplified example, in reality I'm using it to do conversions from string types like so:

packageDb.Quantity = package.package.ElementDeep(Namespace + "PackageQuantity", Namespace + "ActualQuantity", Namespace + "Quantity").ValueOrNull().To<int?>();

If Convert.ChangeType doesn't like Nullable, anyone have any great ideas?

Answer 1

public static T To<T>(this IConvertible obj)
{
    Type t = typeof(T);
    Type u = Nullable.GetUnderlyingType(t);

    if (u != null)
    {
        return (obj == null) ? default(T) : (T)Convert.ChangeType(obj, u);
    }
    else
    {
        return (T)Convert.ChangeType(obj, t);
    }
}