To continue our snippet tutorial series, here's a quick tutorial on how to convert an integer to an enum. This is useful when you've got a number, either from a file or transferred over a socket, and you want to convert that number to an enum.
What we're going to create is a generic method that can convert a number to any type of enum. I like using a generic method for this because now I can convert numbers to any type of enum using the same function and without having to cast the return value for each enum separately.
Here's the function that will be doing all the work:
{
return (T)Enum.ToObject(typeof(T), number);
}
This is a generic function that can convert a number to any type of enum. Let's see some sample code that makes use of this function. First, let's create some enums.
{
Monday,
Tuesday,
Wednesday,
Thursday,
Friday,
Saturday,
Sunday
}
public enum MonthsInYear
{
January,
February,
March,
April,
May,
June,
July,
August,
September,
October,
November,
December
}
Now, let's see some code that uses NumToEnum.
int month = 10;
DaysOfWeek d = NumToEnum<DaysOfWeek>(day);
//d is now DaysOfWeek.Thursday
MonthsInYear m = NumToEnum<MonthsInYear>(month);
//m is now MonthsInYear.November
I know this is something I've needed on several occasions, so hopefully this will help you out as well. Leave any questions in the comments and we'll answer them as best we can.
08/31/2007 - 16:22
Am I doing something wrong, I get this error when I run the above code: "An object reference is required for the nonstatic field, method, or property 'Program.NumToEnum(int)"
08/31/2007 - 16:31
It sounds like you're trying to reference NumToEnum like a static method of the class Program. You can make NumToEnum static by putting the 'static' keyword after 'public' and your code will probably compile. Otherwise you'll need a reference to the Program object for it to work:
p.NumToEnum(int);
08/31/2007 - 22:14
that worked. thx!
10/20/2007 - 06:23
Your solution is cool!
If int number is out of enum member numbers (0 to 6 for DaysOfWeek for example,) how can I detect such an error?
10/20/2007 - 11:38
You can use Enum.IsDefined to check and see if the enum exists before calling NumToEnum. IsDefined takes the value of the enum or the name of the enum has an argument. So you'll have something like:
{
d = NumToEnum<DaysOfWeek>(myNum);
}
else
{
//No enum for number myNum
}
This technique is explained in a little more depth in a follow up tutorial on getting an enum from a string.
12/27/2008 - 18:39
How is this better than just casting to the enum? Like this:
DaysOfWeek dow = (DaysOfWeek) i;
Console.WriteLine( dow ); // “Thursday”
02/20/2009 - 10:56
It's not. I would recommend casting. Live and learn.
03/19/2009 - 01:54
Cool... Works Fine! Thanks Dan
03/19/2009 - 15:48
{
if (Enum.IsDefined(typeof(T), number))
return (T)Enum.ToObject(typeof(T), number);
else
throw new ArgumentException(typeof(T).ToString() + "does not contain a value member = " + number.ToString());
}
public static T GetEnum<T>(string name)
{
if (Enum.IsDefined(typeof(T), name))
return (T)Enum.Parse(typeof(T), name);
else
throw new ArgumentException(typeof(T).ToString() + "does not contain a value member = " + name);
}
08/07/2009 - 12:37
i thought casting comes with a hit to performance?
08/07/2009 - 14:54
In some cases it can, however all casting does is invoke the conversion operator to convert the object to the new type. In the case of enums, the value is stored as a number internally anyway, so the conversion operator should be very quick.
03/04/2010 - 22:20
Enum.IsDefined is a performance killer....refer.
http://blogs.msdn.com/brada/archive/2003/11/29/50903.aspx