Testing if object is of generic type in C#

Question

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

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?

Answer 1

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

return list.GetType().IsGenericType;

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

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

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

Answer 2

return list.GetType().IsGenericType;

Answer 3

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.

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:

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>
    {
    }
}