public static Nullable<T> TryParseNullable<T>(this Nullable<T> t,string input) where T : struct
{
    if (string.IsNullOrEmpty(input))
        return default(T);

    Nullable<T> result = new Nullable<T>();
    try
    {
        IConvertible convertibleString = (IConvertible)input;
        result = new Nullable<T>((T)convertibleString.ToType(typeof(T),CultureInfo.CurrentCulture));
    }
    catch (InvalidCastException) { }
    catch (FormatException) { }

    return result;
}

我已经把它变成了一个扩展方法,它的工作正常,如果我直接调用它：

int? input = new int?().TryParseNullable("12345");

当我尝试使用来自另一个通用函数的上下文中的反射来调用它时,我的问题出现. SO充满了描述如何获取通用方法和静态方法的MethodInfo的答案,但我似乎无法以正确的方式将它们放在一起.
我已经正确地确定了传递的泛型类型本身是一个通用类型(Nullable<>),现在我想使用反射来调用Nullable上的TryParseNullable扩展方法：

public static T GetValue<T>(string name,T defaultValue)
{
    string result = getSomeStringValue(name);
    if (string.IsNullOrEmpty(result)) return defaultValue;

    try
    {
        if (typeof(T).IsGenericType && typeof(T).GetGenericTypeDefinition() == typeof(Nullable<>))
        {
            MethodInfo methodInfo;

            //using the TryParse() of the underlying type works but isn't exactly the way i want to do it
            //------------------------------------------------------------------------------------------- 
            NullableConverter nc = new NullableConverter(typeof(T));
            Type t = nc.UnderlyingType;

            methodInfo = t.GetMethod("TryParse",BindingFlags.Public | BindingFlags.Static,Type.DefaultBinder,new[] { typeof(string),t.MakeByRefType() },null);
            if (methodInfo != null)
            {
                var inputParameters = new object[] { result,null };
                methodInfo.Invoke(null,inputParameters);
                return (T) inputParameters[1];
            }

            //start of the problem area
            //-------------------------

            Type ttype = typeof(T);

            //this works but is undesirable (due to reference to class containing the static method):
            methodInfo = typeof(ParentExtensionsClass).GetMethod("TryParseNullable",BindingFlags.Public | BindingFlags.Static);
            if (methodInfo != null)
                Console.WriteLine(methodInfo);

            //standard way of getting static method,doesn't work (GetMethod() returns null):
            methodInfo = ttype.GetMethod("TryParseNullable",BindingFlags.Public | BindingFlags.Static);
            if (methodInfo != null)
                Console.WriteLine(methodInfo);

            //Jon Skeet's advised method,doesn't work in this case (again GetMethod() returns null):
            //(see footnote for link to this answer)
            methodInfo = ttype.GetMethod("TryParseNullable");
            methodInfo = methodInfo.MakeGenericMethod(ttype);
            if (methodInfo != null)
                Console.WriteLine(methodInfo);

            //another random attempt (also doesn't work):
            methodInfo = ttype.GetMethod("TryParseNullable",new[] { typeof(string) },null);
            if (methodInfo != null)
                Console.WriteLine(methodInfo);
        }

        // if we get this far,then we are not handling the type yet
        throw new ArgumentException("The type " + defaultValue.GetType() + " is not yet supported by GetValue<T>.","T");
    }
    catch (Exception e)
    {
        [snip]
    }
}

有人可以让我摆脱我的苦难吗？
typeof(T)返回正确的类型信息,我想这可能是使用它有点不正确的GetMethod()调用,或者我没有指定正确的参数调用GetMethod().

Link to referenced Jon Skeet answer