Get type of enum in .NET class

Question

Consider the following C# class declaration:

public class MyClass {
    private enum Colours { Red, Green, Blue }
}

Which is sat in a separate class library/DLL.

Given just the typeof(MyClass) object (System.Type), is there any way to check if the class contains an enum called Colours at runtime and if so return it's corresponding System.Type object?

What I'm trying to do is write some generic code that's given the type of a class and determine if contains a specifically named enum inside and then query the values in the enum.

I know how to use Reflection to query things like GetFields, GetProperties etc. but there isn't a GetClasses or GetEnums method in System.Type.

I suspect this kind of information is in the assembly?

And also, once I have the System.Type of the enum, I know how to query the values. It's getting information about the enum itself that's the tricky bit — Rob Nicholson
– Rob Nicholson, Commented Sep 23, 2015 at 14:48

Jeppe Stig Nielsen · Accepted Answer · 2015-09-23 15:00:01Z

11

Just do:

var res = typeof(MyClass).GetNestedType("Colours", BindingFlags.NonPublic);

Test res != null to see if such type exists.

Then test res.IsEnum to see if the nested type is an enum.

Addition: If the nested type is occasionally nested public, use BindingFlags.NonPublic | BindingFlags.Public instead.

edited Sep 23, 2015 at 15:00

answered Sep 23, 2015 at 14:53

Jeppe Stig Nielsen

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2 Comments

Rob Nicholson Over a year ago

Thanks - that just the ticket. I went through the methods in System.Type and my eyes must have glazed over that. Obvious really

Rob Nicholson Over a year ago

Yes, probably best to check for public enums

Binkan Salaryman · Accepted Answer · 2015-09-23 15:39:13Z

I came up with following two methods:

public class MyClass {
    private enum Colours { Red, Green, Blue }

    private class Inner {
        private enum Colours { Black, White }
    }
}

class Program {
    static void Main(string[] args) {
        Type coloursType;
        // 1. enumerator
        coloursType = typeof(MyClass).EnumerateNestedTypes()
            .Where(t => t.Name == "Colours" && t.IsEnum)
            .FirstOrDefault();
        // 2. search method
        coloursType = typeof(MyClass).FindNestedType(t => t.Name == "Colours" && t.IsEnum);

        if(coloursType != null) {
            Console.WriteLine(string.Join(", ", coloursType.GetEnumNames()));
        } else {
            Console.WriteLine("Type not found");
        }
        Console.ReadKey();
    }
}

public static class Extensions {
  public static IEnumerable<Type> EnumerateNestedTypes(this Type type) {
        const BindingFlags flags = BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic;
        Queue<Type> toBeVisited = new Queue<Type>();
        toBeVisited.Enqueue(type);
        do {
            Type[] nestedTypes = toBeVisited.Dequeue().GetNestedTypes(flags);
            for(int i = 0, l = nestedTypes.Length; i < l; i++) {
                Type t = nestedTypes[i];
                yield return t;
                toBeVisited.Enqueue(t);
            }
        } while(toBeVisited.Count != 0);
    }

    public static Type FindNestedType(this Type type, Predicate<Type> filter) {
        const BindingFlags flags = BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic;
        Type[] nestedTypes = type.GetNestedTypes(flags);
        foreach(var nestedType in nestedTypes) {
            if(filter(nestedType)) {
                return nestedType;
            }
        }
        foreach(var nestedType in nestedTypes) {
            Type result = FindNestedType(nestedType, filter);
            if(result != null) {
                return result;
            }
        }
        return null;
    }
}

Alexander Petrov · Accepted Answer · 2015-09-23 14:56:11Z

-1

var types = typeof(MyClass).Assembly.DefinedTypes;

foreach (var type in types)
{
    Console.WriteLine(type.Name);
}

Output:

MyClass
Colours

answered Sep 23, 2015 at 14:56

Alexander Petrov

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1 Comment

Binkan Salaryman Over a year ago

This will trigger a search in the whole assembly where MyClass is defined. I doubt it is the intended solution - "is there any way to check if the class contains an enum called Colours at runtime"

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