Question

For a script that creates controls using reflection, I need to distinguish between

1. Standard value types like Int32
2. Generic nullable types that are based on the ones above, like Int32?
3. Other generic types like List<string>

In .NET 4.5, I can use

myType.IsConstructedGenericType

in combination with

myType.IsValueType

and get

1. False/True
2. True/True
3. True/False

However, IsConstructedGenericType is not available in earlier .NET versions. How can I accomplish this in .NET 4.0?

Answer 1

IsGenericType will do what you want for the examples you’ve given:

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

public class Test
{
    static void Main()
    {
        ShowType(typeof(int));
        ShowType(typeof(int?));
        ShowType(typeof(List<string>));
    }

    static void ShowType(Type type)
    {
        Console.WriteLine("{0} / {1}", type.IsGenericType, type.IsValueType);
    }
}

The difference is that using IsConstructedGenericType would return false for typeof(List<>) whereas IsGenericType will return true. You can use Type.ContainsGenericParameters to distinguish between them in .NET 2+… although even that’s not quite enough, in pathological cases:

class Foo<T> : Dictionary<T, string> {}

Consider typeof(Foo<>).BaseType:

• IsConstructedGenericType: True (it contains one assigned type parameter)
• IsGenericType: True
• ContainsGenericParameters: True (it still contains one unassigned type parameter)

Hopefully this won’t be an issue for you.