CODEWITHSUNDEEP
c#.net-3.5enumscasting
Prof
Prof

Reputation: 5

Casting string value to enumerated value C#

I have a class MyClass which has

public enum Days{Mon, Tue, Wed}

and then a field

public Days dayOfWeek;

From another class in my solution I have a string (myString) value of either 0, 1 or 2. I want to set an instance of MyClass's (called myClassInstance) field dayOfWeek equal to myStringvalue such that 0 means Mon, 1 means Tue...

I have tried

myClassInstance.dayOfWeek = Convert.ToInt32(myString)

and 

myClassInstance.dayOfWeek = (int) myString

but neither work. I'm sure this is straightforward. Why don't these techniques work?

Upvotes: 0

Views: 2556

Answers (7)

bdukes
bdukes

Reputation: 155925

You just need to cast the int to the Days enum after converting it:

myClassInstance.dayOfWeek = (Days)Convert.ToInt32(myString);

You can also use Enum.TryParse (if you're in .NET 4) or Enum.Parse. Depending on how much your trust the incoming data, you may also want to call Enum.IsDefined to make sure that the integer is a valid value of Days (otherwise, in all of these cases, you'll have an instance of Days that doesn't correspond to any of your named values).

Days dayOfWeek;
if (!Enum.TryParse(myString, out dayOfWeek)) {
    dayOfWeek = Days.Mon; // or some other default, or throw
}

myClassInstance.dayOfWeek = dayOfWeek;

Or

myClassInstance.dayOfWeek = (Days)Enum.Parse(typeof(Days), myString);

In addition, as others have mentioned, you may want to consider using the built-in DayOfWeek enum instead of your custom version, if it matches what you really want.

Also, as others have mentioned again, even if it doesn't, Day is a better name based on the .NET naming guidelines, since it isn't a Flags enum.

Upvotes: 6

jason
jason

Reputation: 241641

Try

string s = "0";
Days day = (Days)Enum.Parse(typeof(Days), s);

or

string s = "0";
Days day;
if(!Enum.TryParse(s, out day)) {
    // error handling
}

to gracefully handle the case where s can't be parsed to an instance of Days.

This works per the documentation for Enum.Parse which states

Converts the string representation of the name or numeric value of one or more enumerated constants to an equivalent enumerated object.

Additionally, you can check if the instance of string actually represents a value defined by the enum via

string s = "3";
bool defined = Enum.IsDefined(typeof(Days), s);
// defined is false

Enum.Parse will blindly parse s in this case, even though it doesn't represent a value defined by the enum Days and the cast from the result of Enum.Parse to Days will not fail.

Moreover, there is a built-in enum that represents the days of the week. This enum is System.DayOfWeek. I would suggest using this.

Finally, if for some reason you can't use System.DayOfWeek, you should at a minimum rename your enum to Day instead of Days (remove the pluralization). Only enums that represent flags should be pluralized. Note that the variable day above represents a day, and it does not represent days. This is why you should rename the enum to Day. This is consistent with the naming conventions that most C# and .NET programmers use.

Upvotes: 9

Joe
Joe

Reputation: 57169

This should work

myClassInstance.dayOfWeek = Enum.Parse(typeof(Days), myString);

Enump.Parse

Upvotes: 0

F.B. ten Kate
F.B. ten Kate

Reputation: 2032

What you want to do is cast the string to an int (or tryparse if you want to do it in a nice way)

Then use the Following code to set the enum value:

(Days)Enum.ToObject(typeof(Days), intValue);

Upvotes: 0

pstrjds
pstrjds

Reputation: 17428

You need to cast the int to Days:

myClassInstance.dayOfWeek = (Days)Convert.ToInt32(myString);

Upvotes: 0

Brian Clapper
Brian Clapper

Reputation: 26211

Try:

Days d = (Days)Enum.Parse(typeof(Days), myString);

A more complete example is here.

Upvotes: 2

bendewey
bendewey

Reputation: 40235

Try

myClassInstance.dayOfWeek = (Days)int.Parse(myString);

Do you know there is already an Enum that you can resuse called DayOfWeek (http://msdn.microsoft.com/en-us/library/system.dayofweek.aspx)

Upvotes: 2

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