Initial Value of an Enum

Question

I have a class with a property which is an enum

The enum is

/// 

/// All available delivery actions
/// 
public enum E         


        

Answer 1

Enum fields are initialized as zero; an if you don't specify values in an enum, they start at zero (Email = 0, SharePoint=1, etc).

Thus by default any field you do initialize yourself will be Email. It is relatively common to add None=0 for such cases, or alternatively use Nullable<T>; i.e.

/// <summary>
/// All available delivery actions
/// </summary>
public enum EnumDeliveryAction
{
    /// <summary>
    /// Not specified
    /// </summary>
    None,

    /// <summary>
    /// Tasks with email delivery action will be emailed
    /// </summary>
    Email,

    /// <summary>
    /// Tasks with SharePoint delivery action 
   /// </summary>
   SharePoint
}

You should also be sure to never treat your last expected value as a default; i.e.

switch(action) {
    case EnumDeliveryAction.Email; RunEmail(); break;
    default: RunSharePoint(); break;
}

this should be:

switch(action) {
    case EnumDeliveryAction.Email; RunEmail(); break;
    case EnumDeliveryAction.SharePoint; RunSharePoint(); break;
    default: throw new InvalidOperationException(
          "Unexpected action: " + action);
}

Answer 2

By default only reference types are nullable types. If you want a variable to allow nulls you have to define it as nullable using the "?" character (for this you need C# 2.0 or up).

enum MyEnum
{
    ValueOne,
    ValueTwo
}

and in your class

MyEnum? myvariable = null;

Answer 3

You can start your enums at any value (such as 1), but when they represent a lookup value in a Database, you generally want them to match up.

I generally declare the first Enum as None ( = 0) when it makes sense to do so, as per the .Net Framework Design guidelines.

Answer 4

Best practice (as advised by Code Analysis) is to always have a default value in your enums, which represent an unset value.

So in your case, you might have:

public enum EnumDeliveryAction
   {

    /// <summary>
    /// Default value
    /// </summary>
    NotSet,

    /// <summary>
    /// Tasks with email delivery action will be emailed
    /// </summary>
    Email,

    /// <summary>
    /// Tasks with SharePoint delivery action 
   /// </summary>
   SharePoint
  }

As an aside, you shouldn't prefix the name of the enum with Enum. You might consider changing to:

public enum DeliveryAction;

Answer 5

My C++ teacher in college (11 years ago) told me that the linker replaces enum with their actual type:

typedef static const int enum;

Thus, any time you write something like enum MY_VAL = 5;, you could easily replace with static const int MY_VAL = 5; (but that just makes your code longer...).

Anyway, the default value of any int is 0.

Answer 6

Enums are a value type, like ints. You need to make it nullable so as not to default to the first (or 0-defined) enum member.

public class MyClass
{
   public EnumDeliveryAction? DeliveryAction { get; set;}
}