How to represent an Enum in an Interface?

Question

How could I define an Interface which has a method that has Enum as a paramater when enums cannot be defined in an interface?

For an Enum is not a reference type so an Object type cannot be used as the type for the incoming param, so how then?

score 50 · Answer 1 · answered Jul 09 '10 at 20:39

50

public enum MyEnum
{
  Hurr,
  Durr
}

public interface MyInterface
{
  void MyMethod(MyEnum value);
}

If this isn't what you're talking about doing, leave a comment so people can understand what your issue is. Because, while the enum isn't defined within the interface, this is a completely normal and acceptable design.

answered Jul 09 '10 at 20:39

+1 I created an iEventLogTypes `class` as helper for my IEventLog `interface`. Right now it only contains an `enum`, but I can add any "types" that I need within my interface. I like sticking the enum in a "similar named" class so that the enum is more tightly bound to the specific interface, even if it's in "name only". – franji1 Oct 16 '15 at 15:12
I don't know why, but I never thought of creating the Enum outside of the class declaration, but within the namespace before. – Reahreic Jun 15 '23 at 19:06

score 24 · Accepted Answer · answered Jul 09 '10 at 20:32

24

interface MyInterface
{
    void MyMethod(Enum @enum);
}

answered Jul 09 '10 at 20:32

Yuriy Faktorovich

67,283
14
105
142

4

what's the @ for? I tried to look it up in MSDN...sorry if this seems trivial. I'm new to creating interfaces. – PositiveGuy Jul 09 '10 at 20:34
11

anticipating your question: `@enum` is the name of the variable. There is nothing special about that syntax – BlueRaja - Danny Pflughoeft Jul 09 '10 at 20:34
34

@coffeeaddict: It allows you to use a reserved word for a parameter name. Without it, you'd get a compiler error (unless you rename "enum" to something else) – Reed Copsey Jul 09 '10 at 20:35
1

still Enum is a type declared in a different namespace even. The Enum type is yet declared outside an interface. – Lucas Locatelli Feb 23 '15 at 19:52
Am wondering whether this accepted answer is what the user who posted this question is looking for? – Carthic Dec 12 '19 at 11:24

score 10 · Answer 3 · edited Nov 29 '19 at 13:32

Another solution could be to use Generic types:

public enum MyEnum
{
    Foo,
    Bar
}

public interface IDummy<EnumType>
{
    void OneMethod(EnumType enumVar);
}

public class Dummy : IDummy<MyEnum>
{
    public void OneMethod(MyEnum enumVar)
    {
        // Your code
    }
}

Also, since C# 7.3, you can add a generic constraint to accept only Enum types:

public interface IDummy<EnumType> where EnumType : Enum
{
    void OneMethod(EnumType enumVar);
}

score 3 · Answer 4 · answered Sep 06 '17 at 15:18

Defining an enum is like defining a class or defining an interface. You could just put it in one of your class files, inside the namespace but outside the class definition, but if several classes use it, which one do you put it in, and whichever you choose you will get "Type name does not match file name" warnings. So the "right" way to do it is to put it in its own file, as you would a class or an interface:

MyEnum.cs

namespace MyNamespace { internal enum MyEnum { Value1, Value2, Value3, Value4, Value5 }; } Then any interfaces or classes within the namespace can access it.

score 0 · Answer 5 · edited May 23 '17 at 10:30

0

If you're talking about generic interfaces and the fact that C# doesn't let you constrain generic types to be enums, the answers to this question include two different work-arounds.

edited May 23 '17 at 10:30

Community

1
1

answered Jul 09 '10 at 20:51

Joel Mueller

28,324
9
63
88

It does constrain, you just can't define the type inside the interface. The same way you do when you create an interface, add a namespace that contain a specific type then add that in the parameters or return types. – Lucas Locatelli Feb 23 '15 at 19:49

score 0 · Answer 6 · answered Sep 26 '22 at 12:14

You must implement the enum in both side and refer the Interface namespace, eg:

public interface IConfigProvider
{
    enum OUType
    {
        Prop1,
        Prop2
    };


    string GetConfig(OUType outType);
}

public class ConfigProvider
{
    enum OUType
    {
       Prop1,
       Prop2
    };
    
    public string GetConfig(IConfigProvider.OUType outType)
    {
        ...
    }
    
}

Usage:

configProvider.GetConfig(IConfigProvider.OUType.Prop1)

How to represent an Enum in an Interface?

6 Answers6

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