Question

C# Enum question

Asked by: simonm_jp

I have the following enum

public enum Category
{
     Unknown = 0,
     LocationType = 1,
     PhoneType = 2
}

then I have a class which contains an attribute as per the following:   private Category classCategory;

I know if I request "Category.LocationType" I will get an integer of '2' returned ... how would I pass the enum an integer value, such as 2, so that it returns "LocationType" as a string?

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Asked On
2005-09-11 at 20:56:59ID21557816
Tags

enum

Topic

C# Programming Language

Participating Experts
4
Points
500
Comments
13

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Answers

 

by: aseem_dayalPosted on 2005-09-11 at 22:19:08ID: 14861818

Hi,

This is what you need to do :


Category objCategory = new Category(); //standard variable initialization


objCategory=(Category) 1; // passing an integer value to the variable, with explicit typecasting


Console.WriteLine(objCategory.ToString()); //this statement shall print "LocationType" on the
                                                               //console as a string

 

by: jatinderalaghPosted on 2005-09-11 at 23:50:53ID: 14862071

// Enums are value types no need for using new operator
                  // This is prefered way of initalizing enums
                  Category myCategory = Category.LocationType;
                  myCategory = (Category)1;// or you can initailize in this way not recomended
                  // You can retrieve the value as int by typecasting
                  int catInt = (int)myCategory;
                  // Do the comparison as
                  if(myCategory == Category.LocationType)
                  {
                        // Do the operation
                  }

// Use ToString function to get the EnumbyName
myCategory.ToString(); // this will return LocationType

 

by: DaeljanPosted on 2005-09-12 at 01:55:30ID: 14862472

If you really need to do this, then the Enum sould also have the value "InvalidValue" or something similar. You should then write a method called

Category IntToEnumCategory(int intVal)

To retrieve the correct enum value. This would be a switch, the default value being "InvalidValue". Its the safe way.

you can also use Enum.Parse() to convert a text string to the enum too. That may throw an exception if the enum value is not found.

 

by: simonm_jpPosted on 2005-09-12 at 03:02:21ID: 14862752

Hi jatinderalagh,
To be honest, from the outset aseem_dayal's code appears to be more elegant, and completes the task in only three lines of code.  Could you please explain why your method of instantiation is the "preferred" way?
Thanks,

 

by: DaeljanPosted on 2005-09-12 at 03:05:45ID: 14862765

objCategory=(Category) 1;

This is a dangerous cast and it will throw an exception if the int value does not coincide with the enum

 

by: jatinderalaghPosted on 2005-09-12 at 03:39:22ID: 14862882

@simonm_jp : Right the code i have given just shows different way of doing things. Read the inline comments
and initializing the enum in this way
objCategory=(Category) 1;

thanks to Daeljan already explained the cause.

jatinder

 

by: simonm_jpPosted on 2005-09-12 at 03:51:42ID: 14862915

Thanks everyone,
In this case the values are read from a DropDownList, which was originally populated from the Category enum ... so I guess we are safe (this time).

To make it safer, would it be better to enclose the intialization in a try-catch block ..?

try
{
   objCategory=((Category)Convert.ToInt32(ddlCategory.SelectedItem.Value));
}
catch (Exception e) { objCategory=Category.Unknown; } //similar to Daeljan's "InvalidValue"

 

by: steelheart38Posted on 2005-09-12 at 05:08:25ID: 14863251

to convert an integer to an Enum type i usually do it by passing a string representation of the number.. and not integer..but maybe it would help

------------------------------
string Number = "8";
string EnumEquivalent = Convert.ToString(Enum.Parse(typeof(LocationType),Number));
------------------------------

Enum.Parse(typeof(LocationType),Number) returns the enumeration
and using Convert.ToString(...) returns the string

 

by: simonm_jpPosted on 2005-09-12 at 06:13:40ID: 14863660

Thanks steelheart38 ... so could I do the following?

int value = ddlCategory.SelectedItem.Value;  // eg. 1
if (Category.IsDefined(typeof(Category),value ))
{
   Category _category = Enum.Parse(typeof(Category),Convert.ToString(value));
   classCategory = _category;     // classCategory is now equal to Category.LocationType
}
else  
{
   classCategory = Category.Unknown;
}

 

by: steelheart38Posted on 2005-09-12 at 07:06:52ID: 14864063

// -- make sure that classCategory is of "Category" data type
Category classCategory;

// -- "value" is a reserved word so change it to another variable name (eg. myValue)
int myValue = ddlCategory.SelectedItem.Value;

// -- i think the syntax is Enum.IsDefined(...) (not Category.IsDefined(...)) unless you have overriden it (not sure if its
// -- possible). But i usually just stick with Enum.IsDefined(...)
if (Enum.IsDefined(typeof(Category),myValue))
{
    // -- you can assign the value to classCategory, no need to create a temporary _category
    classCategory = (Category)Enum.Parse(typeof(Category),Convert.ToString(myValue));
}

else  
{
    classCategory = Category.Unknown;
}

// -- tried it and it works, just post here if you encounter errors.. but basically this would do it

 

by: steelheart38Posted on 2005-09-12 at 07:15:03ID: 14864137

// -- btw..i forgot to comment this line
----------
Category _category = Enum.Parse(typeof(Category),Convert.ToString(value));
----------
// -- Enum.Parse returns an enumeration that you still need to cast to your enumeration. so it should be
----------
classCategory = (Category)Enum.Parse(typeof(Category),Convert.ToString(value));

 

by: simonm_jpPosted on 2005-09-13 at 01:20:44ID: 14869968

Thanks, thats the answer I was after.

 

by: steelheart38Posted on 2005-09-13 at 01:22:50ID: 14869981

i hope that was helpful..c",)

Good luck.

20120131-EE-VQP-002

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