在C#中,Type.FullName何时返回null？

因此，我立即注意到MSDN引用在其案例列表中两次包含“或”，但是花了我很长时间才意识到原因。现实情况是，存在三种主要情况，这三种情况之一被分为另外三种情况。使用更清晰的标点符号，情况是

通用类型参数；

基于类型参数的数组类型，指针类型或byref类型；要么

不是通用类型定义，但包含未解析的类型参数的通用类型。

我了解第一种情况，Rahul的回答将我定向到了MSDN博客文章，该文章解释并给出了最后一种情况的两个示例，现在我可以给出其余情况的示例。

using System;
using System.Linq;

namespace ConsoleApplication {

  public class GenericClass {
    public void ArrayMethod(T[] parameter) { }
    public void ReferenceMethod(ref T parameter) { }
  }

  public class AnotherGenericClass : GenericClass { }

  public static class Program {

    public static void Main(string[] args) {
      GenericTypeParameter();
      ArrayTypeBasedOnTypeParameter();
      PointerTypeBasedOnTypeParameter();
      ByRefTypeBasedOnTypeParameter();
      NongenericTypeDefinitionWithUnresolvedTypeParameters();
      Console.ReadKey();
    }

    public static void GenericTypeParameter() {
      var type = typeof(GenericClass<>)
        .GetGenericArguments()
        .First();
      PrintFullName("Generic type parameter", type);
    }

    public static void ArrayTypeBasedOnTypeParameter() {
      var type = typeof(GenericClass<>)
        .GetMethod("ArrayMethod")
        .GetParameters()
        .First()
        .ParameterType;
      PrintFullName("Array type based on type parameter", type);
    }

    /*
     * Would like an actual example of a pointer to a generic type,
     * but this works for now.
     */
    public static void PointerTypeBasedOnTypeParameter() {
      var type = typeof(GenericClass<>)
        .GetGenericArguments()
        .First()
        .MakePointerType();
      PrintFullName("Pointer type based on type parameter", type);
    }

    public static void ByrefTypeBasedOnTypeParameter() {
      var type = typeof(GenericClass<>)
        .GetMethod("ReferenceMethod")
        .GetParameters()
        .First()
        .ParameterType;
      PrintFullName("ByRef type based on type parameter", type);
    }

    private static void NongenericTypeDefinitionWithUnresolvedTypeParameters() {
      var type = typeof(AnotherGenericClass<>).BaseType;
      PrintFullName("Nongeneric type definition with unresolved type parameters", type);
    }

    public static void PrintFullName(string name, Type type) {
      Console.WriteLine(name + ":");
      Console.WriteLine("--Name: " + type.Name);
      Console.WriteLine("--FullName: " + (type.FullName ?? "null"));
      Console.WriteLine();
    }
  }
}

/***Output***
Generic type parameter:
--Name: T
--FullName: null

Array type based on type parameter:
--Name: T[]
--FullName: null

Pointer type based on type parameter:
--Name: T*
--FullName: null

Byref type based on type parameter:
--Name: T&
--FullName: null

Nongeneric type definition with unresolved type parameters:
--Name: GenericClass`1
--FullName: null
***Output***/