测试对象是否为 C# 中的泛型类型

Testing if object is of generic type in C#

提问by Richbits

I would like to perform a test if an object is of a generic type. I've tried the following without success:

我想测试一个对象是否是泛型类型。我尝试了以下但没有成功：

public bool Test()
{
    List<int> list = new List<int>();
    return list.GetType() == typeof(List<>);
}

What am I doing wrong and how do I perform this test?

我做错了什么，我该如何进行这个测试？

采纳答案by Mehrdad Afshari

If you want to check if it's an instance of a generic type:

如果要检查它是否是泛型类型的实例：

return list.GetType().IsGenericType;

If you want to check if it's a generic List<T>:

如果你想检查它是否是一个通用的List<T>：

return list.GetType().GetGenericTypeDefinition() == typeof(List<>);

As Jon points out, this checks the exact type equivalence. Returning falsedoesn't necessarily mean list is List<T>returns false(i.e. the object cannot be assigned to a List<T>variable).

正如 Jon 指出的那样，这会检查确切的类型等效性。返回false并不一定意味着list is List<T>返回false（即对象不能分配给List<T>变量）。

回答by Stan R.

return list.GetType().IsGenericType;

回答by Jon Skeet

I assume that you don't just want to know if the type is generic, but if an object is an instance of a particular generic type, without knowing the type arguments.

我假设您不只是想知道类型是否是泛型，而是想知道对象是否是特定泛型类型的实例，而不知道类型参数。

It's not terribly simple, unfortunately. It's not too bad if the generic type is a class (as it is in this case) but it's harder for interfaces. Here's the code for a class:

不幸的是，这并不是非常简单。如果泛型类型是一个类（就像在这种情况下一样），那还不错，但是对于接口来说就更难了。这是一个类的代码：

using System;
using System.Collections.Generic;
using System.Reflection;

class Test
{
    static bool IsInstanceOfGenericType(Type genericType, object instance)
    {
        Type type = instance.GetType();
        while (type != null)
        {
            if (type.IsGenericType &&
                type.GetGenericTypeDefinition() == genericType)
            {
                return true;
            }
            type = type.BaseType;
        }
        return false;
    }

    static void Main(string[] args)
    {
        // True
        Console.WriteLine(IsInstanceOfGenericType(typeof(List<>),
                                                  new List<string>()));
        // False
        Console.WriteLine(IsInstanceOfGenericType(typeof(List<>),
                                                  new string[0]));
        // True
        Console.WriteLine(IsInstanceOfGenericType(typeof(List<>),
                                                  new SubList()));
        // True
        Console.WriteLine(IsInstanceOfGenericType(typeof(List<>),
                                                  new SubList<int>()));
    }

    class SubList : List<string>
    {
    }

    class SubList<T> : List<T>
    {
    }
}

EDIT: As noted in comments, this may work for interfaces:

编辑：如评论中所述，这可能适用于接口：

foreach (var i in type.GetInterfaces())
{
    if (i.IsGenericType && i.GetGenericTypeDefinition() == genericType)
    {
        return true;
    }
}

I have a sneaking suspicion there may be some awkward edge cases around this, but I can't find one it fails for right now.

我偷偷怀疑这可能有一些尴尬的边缘情况，但我现在找不到它失败的情况。

回答by David Desmaisons

You can use shorter code using dynamic althougth this may be slower than pure reflection:

您可以使用动态使用较短的代码，尽管这可能比纯反射慢：

public static class Extension
{
    public static bool IsGenericList(this object o)
    {
       return IsGeneric((dynamic)o);
    }

    public static bool IsGeneric<T>(List<T> o)
    {
       return true;
    }

    public static bool IsGeneric( object o)
    {
        return false;
    }
}



var l = new List<int>();
l.IsGenericList().Should().BeTrue();

var o = new object();
o.IsGenericList().Should().BeFalse();

回答by Wiebe Tijsma

These are my two favorite extension methods that cover most edge cases of generic type checking:

这是我最喜欢的两个扩展方法，它们涵盖了泛型类型检查的大多数边缘情况：

Works with:

适用于：

• Multiple (generic) interfaces
• Multiple (generic) base classes

• Has an overload that will 'out' the specific generic type if it returns true (see unit test for samples):

  public static bool IsOfGenericType(this Type typeToCheck, Type genericType)
  {
      Type concreteType;
      return typeToCheck.IsOfGenericType(genericType, out concreteType); 
  }
  
  public static bool IsOfGenericType(this Type typeToCheck, Type genericType, out Type concreteGenericType)
  {
      while (true)
      {
          concreteGenericType = null;
  
          if (genericType == null)
              throw new ArgumentNullException(nameof(genericType));
  
          if (!genericType.IsGenericTypeDefinition)
              throw new ArgumentException("The definition needs to be a GenericTypeDefinition", nameof(genericType));
  
          if (typeToCheck == null || typeToCheck == typeof(object))
              return false;
  
          if (typeToCheck == genericType)
          {
              concreteGenericType = typeToCheck;
              return true;
          }
  
          if ((typeToCheck.IsGenericType ? typeToCheck.GetGenericTypeDefinition() : typeToCheck) == genericType)
          {
              concreteGenericType = typeToCheck;
              return true;
          }
  
          if (genericType.IsInterface)
              foreach (var i in typeToCheck.GetInterfaces())
                  if (i.IsOfGenericType(genericType, out concreteGenericType))
                      return true;
  
          typeToCheck = typeToCheck.BaseType;
      }
  }
  

• 多个（通用）接口
• 多个（通用）基类

• 有一个重载，如果它返回 true，它将“输出”特定的泛型类型（请参阅示例的单元测试）：

  public static bool IsOfGenericType(this Type typeToCheck, Type genericType)
  {
      Type concreteType;
      return typeToCheck.IsOfGenericType(genericType, out concreteType); 
  }
  
  public static bool IsOfGenericType(this Type typeToCheck, Type genericType, out Type concreteGenericType)
  {
      while (true)
      {
          concreteGenericType = null;
  
          if (genericType == null)
              throw new ArgumentNullException(nameof(genericType));
  
          if (!genericType.IsGenericTypeDefinition)
              throw new ArgumentException("The definition needs to be a GenericTypeDefinition", nameof(genericType));
  
          if (typeToCheck == null || typeToCheck == typeof(object))
              return false;
  
          if (typeToCheck == genericType)
          {
              concreteGenericType = typeToCheck;
              return true;
          }
  
          if ((typeToCheck.IsGenericType ? typeToCheck.GetGenericTypeDefinition() : typeToCheck) == genericType)
          {
              concreteGenericType = typeToCheck;
              return true;
          }
  
          if (genericType.IsInterface)
              foreach (var i in typeToCheck.GetInterfaces())
                  if (i.IsOfGenericType(genericType, out concreteGenericType))
                      return true;
  
          typeToCheck = typeToCheck.BaseType;
      }
  }
  

Here's a test to demonstrate the (basic) functionality:

这是一个演示（基本）功能的测试：

 [Test]
    public void SimpleGenericInterfaces()
    {
        Assert.IsTrue(typeof(Table<string>).IsOfGenericType(typeof(IEnumerable<>)));
        Assert.IsTrue(typeof(Table<string>).IsOfGenericType(typeof(IQueryable<>)));

        Type concreteType;
        Assert.IsTrue(typeof(Table<string>).IsOfGenericType(typeof(IEnumerable<>), out concreteType));
        Assert.AreEqual(typeof(IEnumerable<string>), concreteType);

        Assert.IsTrue(typeof(Table<string>).IsOfGenericType(typeof(IQueryable<>), out concreteType));
        Assert.AreEqual(typeof(IQueryable<string>), concreteType);


    }