Best way to enum NSString

Question

Im digging for ways to enum objc object such as NSString, I remember there a new feature in a version of Xcode4+ which offering a new way to enum , but not clearly. Anyone know

Answer 1

Update in 2017

Recent down votes drew my attention, and I'd like to add that enum is really easy to work with String now:

enum HTTPMethod: String {
    case GET, POST, PUT
}

HTTPMethod.GET.rawValue == "GET" // it's true

Original Answer

Unfortunately I ended up using:

#define HLCSRestMethodGet       @"GET"
#define HLCSRestMethodPost      @"POST"
#define HLCSRestMethodPut       @"PUT"
#define HLCSRestMethodDelete    @"DELETE"
typedef NSString*               HLCSRestMethod;

I know this is not what OP asked, but writing actual code to implement enum seems to be an overkill to me. I would consider enum as a language feature (from C) and if I have to write code, I would come up with some better classes that does more than enum does.

Update

Swift version seems to be prettier, although the performance can never be as good.

struct LRest {
    enum HTTPMethod: String {
        case Get = "GET"
        case Put = "PUT"
        case Post = "POST"
        case Delete = "DELETE"
    }
    struct method {
        static let get = HTTPMethod.Get
        static let put = HTTPMethod.Put
        static let post = HTTPMethod.Post
        static let delete = HTTPMethod.Delete
    }

}

Answer 2

Recommended way from apple docs:

You use the NS_TYPED_ENUM to group constants with a raw value type that you specify. Use NS_TYPED_ENUM for sets of constants that can't logically have values added in a Swift extension, and use NS_TYPED_EXTENSIBLE_ENUM for sets of constants that can be expanded in an extension. Apple docs

typedef NSString *MyEnum NS_TYPED_ENUM;
extern MyEnum const MyEnumFirstValue;
extern MyEnum const MyEnumSecondValue;
extern MyEnum const MyEnumThirdValue;

in the .h file. Define your strings in the .m file

MyEnum const MyEnumFirstValue = @"MyEnumFirstValue"
MyEnum const MyEnumSecondValue = @"MyEnumSecondValue";
MyEnum const MyEnumThirdValue = @"MyEnumThirdValue";

Works as expected in both Objective-C

- (void)methodWithMyEnum:(MyEnum)myEnum { }

and Swift

func method(_ myEnum: MyEnum) { }

Answer 3

See my answer at enum Values to NSString (iOS) - I believe that might be a more elegant solution to this issue.

Answer 4

OK, I answered myself. Guess I make a mistake.

This is the new feature I mentioned above:

typedef enum Language : NSUInteger{
     ObjectiveC,
     Java, 
     Ruby, 
     Python, 
    Erlang 
}Language;

It's just a new syntax for enum in Xcode 4.4, but I'm so foolish to think we can exchange "NSUInteger" to "NSString".

So here is the way I found that works:

http://longweekendmobile.com/2010/12/01/not-so-nasty-enums-in-objective-c/

// Place this in your .h file, outside the @interface block
typedef enum {
    JPG,
    PNG,
    GIF,
    PVR
} kImageType;
#define kImageTypeArray @"JPEG", @"PNG", @"GIF", @"PowerVR", nil

...

// Place this in the .m file, inside the @implementation block
// A method to convert an enum to string
-(NSString*) imageTypeEnumToString:(kImageType)enumVal
{
    NSArray *imageTypeArray = [[NSArray alloc] initWithObjects:kImageTypeArray];
    return [imageTypeArray objectAtIndex:enumVal];
}

// A method to retrieve the int value from the NSArray of NSStrings
-(kImageType) imageTypeStringToEnum:(NSString*)strVal
{
    NSArray *imageTypeArray = [[NSArray alloc] initWithObjects:kImageTypeArray];
    NSUInteger n = [imageTypeArray indexOfObject:strVal];
    if(n < 1) n = JPG;
    return (kImageType) n;
}

FYI. The original author of the second example code created a category for enum handling. Just the thing for adding to your very own NSArray class definition.

@interface NSArray (EnumExtensions)

- (NSString*) stringWithEnum: (NSUInteger) enumVal;
- (NSUInteger) enumFromString: (NSString*) strVal default: (NSUInteger) def;
- (NSUInteger) enumFromString: (NSString*) strVal;

@end

@implementation NSArray (EnumExtensions)

- (NSString*) stringWithEnum: (NSUInteger) enumVal
{
    return [self objectAtIndex:enumVal];
}

- (NSUInteger) enumFromString: (NSString*) strVal default: (NSUInteger) def
{
    NSUInteger n = [self indexOfObject:strVal];
    if(n == NSNotFound) n = def;
    return n;
}

- (NSUInteger) enumFromString: (NSString*) strVal
{
    return [self enumFromString:strVal default:0];
}

@end

Answer 5

I think you are looking for the inline array function. eg

@[@"stringone",@"stringtwo",@"stringthree"];

if not, i'm not sure you can enum objects.

you could however have a static array of strings and have the enum reference object at index.

Answer 6

Alternative way to use struct:

extern const struct AMPlayerStateReadable
{
    __unsafe_unretained NSString *ready;
    __unsafe_unretained NSString *completed;
    __unsafe_unretained NSString *playing;
    __unsafe_unretained NSString *paused;
    __unsafe_unretained NSString *broken;
} AMPlayerState;

const struct AMPlayerStateReadable AMPlayerState =
{
    .ready = @"READY",
    .completed = @"COMPLETE",
    .playing = @"PLAYING",
    .paused = @"PAUSED",
    .broken = @"BROKEN"
};

Then you can use like this:

NSString *status = AMPlayerState.ready;

Easy to use, readable. Would be nice if someone update/edit answer with advantages/disadvantages of this approach.