How to make a Swift String enum available in Objective-C?

Question

I have this enum with String values, which will be used to tell an API method that logs to a server what kind of serverity a message has. I'm using Swift 1.2, so enums can be mapped to Objective-C

@objc enum LogSeverity : String {
    case Debug = "DEBUG"
    case Info = "INFO"
    case Warn = "WARN"
    case Error = "ERROR"
}

I get the error

@objc enum raw type String is not an integer type

I haven't managed to find anywhere which says that only integers can be translated to Objective-C from Swift. Is this the case? If so, does anyone have any best-practice suggestion on how to make something like this available in Objective-C?

Jafar Khoshtabiat · Accepted Answer · 2020-02-18 08:51:00Z

104

One of the solutions is to use the RawRepresentable protocol.

It's not ideal to have to write the init and rawValue methods but that allows you to use this enum as usual in both Swift and Objective-C.

@objc public enum LogSeverity: Int, RawRepresentable {
    case debug
    case info
    case warn
    case error

    public typealias RawValue = String

    public var rawValue: RawValue {
        switch self {
            case .debug:
                return "DEBUG"
            case .info:
                return "INFO"
            case .warn:
                return "WARN"
            case .error:
                return "ERROR"
        }
    }

    public init?(rawValue: RawValue) {
        switch rawValue {
            case "DEBUG":
                self = .debug
            case "INFO":
                self = .info
            case "WARN":
                self = .warn
            case "ERROR":
                self = .error
            default:
                return nil
        }
    }
}

edited Feb 18, 2020 at 8:51

Jafar Khoshtabiat

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answered Jul 20, 2016 at 21:01

Remy Cilia

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13 Comments

Gobe Over a year ago

I really like this approach. To make it perfect, one may avoid some code duplication by defining a dictionary of type [LogSeverity: String] and then the rawValue and init? methods can be defined by a single line.

Daniel Sanchez Over a year ago

@Gobe can you share the example of how to write the rawValue and init? methods in a single line, please?

Gobe Over a year ago

@DanielSanchez if you have an enum of type LogSeverity which is raw representable by Strings, and you define once a dictionary of type [LogSeverity: String], then the rawValue is simply myDictionary[self] and the init is self = myDictionary.first(where: { $0.value == rawValue })

Jafar Khoshtabiat Over a year ago

It seems a nice answer, but I'm getting strange bad_access crashes after trying this out.

Aaban Tariq Murtaza Over a year ago

rawValue isn't accessible in objc.

|

Martin R · Accepted Answer · 2017-11-06 20:51:20Z

63

From the Xcode 6.3 release notes (emphasis added):

Swift Language Enhancements

...
Swift enums can now be exported to Objective-C using the @objc attribute. @objc enums must declare an integer raw type, and cannot be generic or use associated values. Because Objective-C enums are not namespaced, enum cases are imported into Objective-C as the concatenation of the enum name and case name.

edited Nov 6, 2017 at 20:51

answered May 27, 2015 at 10:53

Martin R

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2 Comments

Zack Shapiro Over a year ago

Page cannot be found on link

Martin R May 9 at 7:43

@ZackShapiro: The link has been updated.

David · Accepted Answer · 2015-10-22 03:44:26Z

20

Here's a solution that works.

@objc public enum ConnectivityStatus: Int {
    case Wifi
    case Mobile
    case Ethernet
    case Off

    func name() -> String {
        switch self {
        case .Wifi: return "wifi"
        case .Mobile: return "mobile"
        case .Ethernet: return "ethernet"
        case .Off: return "off"
        }
    }
}

answered Oct 22, 2015 at 3:44

David

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8 Comments

Stephen Paul Over a year ago

And how would the name() function be called in Objective-C?

Cameron Askew Over a year ago

@David but you cannot call name() in objc

Priyal Over a year ago

@Chuck even public function will not expose the method.

strangetimes Over a year ago

Don't know why this answer got up voted, this is not accessible from Obj-C

guru Over a year ago

Yes i also can also not call from objc

|

BLC · Accepted Answer · 2015-10-21 14:24:55Z

14

Here is work around if you really want to achieve the goal. However, you can access the enum values in objects that Objective C accepts, not as actual enum values.

enum LogSeverity : String {

    case Debug = "DEBUG"
    case Info = "INFO"
    case Warn = "WARN"
    case Error = "ERROR"

    private func string() -> String {
        return self.rawValue
    }
}

@objc
class LogSeverityBridge: NSObject {

    class func Debug() -> NSString {
        return LogSeverity.Debug.string()
    }

    class func Info() -> NSString {
        return LogSeverity.Info.string()
    }

    class func Warn() -> NSString {
        return LogSeverity.Warn.string()
    }

    class func Error() -> NSString {
        return LogSeverity.Error.string()
    }
}

To call :

NSString *debugRawValue = [LogSeverityBridge Debug]

edited Oct 21, 2015 at 14:24

answered Oct 21, 2015 at 14:00

BLC

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2 Comments

Chris Prince Over a year ago

The problem I see with this is that you can't have variables of type LogSeverity, but otherwise OK.

Hendrix Over a year ago

This worked for me with some minor alterations.

@objcMembers public class LogSeverityBridge: NSObject {      static func debug() -> String {         return TravelerProtectionLevel.premium.rawValue     }

David Hoerl · Accepted Answer · 2022-07-29 20:37:17Z

9

If you don't mind to define the values in (Objective) C, you can use the NS_TYPED_ENUM macro to import constants in Swift.

For example:

.h file

typedef NSString *const ProgrammingLanguage NS_TYPED_ENUM;

FOUNDATION_EXPORT ProgrammingLanguage ProgrammingLanguageSwift;
FOUNDATION_EXPORT ProgrammingLanguage ProgrammingLanguageObjectiveC;

.m file

ProgrammingLanguage ProgrammingLanguageSwift = @"Swift";
ProgrammingLanguage ProgrammingLanguageObjectiveC = @"ObjectiveC";

In Swift, this is imported as a struct as such:

struct ProgrammingLanguage: RawRepresentable, Equatable, Hashable {
    typealias RawValue = String

    init(rawValue: RawValue)
    var rawValue: RawValue { get }
    
    static var swift: ProgrammingLanguage { get }
    static var objectiveC: ProgrammingLanguage { get }
}

Although the type is not bridged as an enum, it feels very similar to one when using it in Swift code.

You can read more about this technique in Grouping Related Objective-C Constants

edited Jul 29, 2022 at 20:37

David Hoerl

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answered Feb 9, 2018 at 20:45

RvdB

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3 Comments

Tom Kraina Over a year ago

This is exactly the approach I was looking for!

David Hoerl Over a year ago

Of all the solutions I like this one the best, using it in a big mixed Objective-C and Swift project.

DEAD10CC Over a year ago

I use NS_TYPED_EXTENSIBLE_ENUM to be able to add more cases over time. Is there a way to make extensions done in Swift available to Objective-C? Marking them with @objc does not work since the extended type is the bridged struct and not an Objective-C type like NSString.

shim · Accepted Answer · 2017-01-25 22:27:06Z

5

Code for Xcode 8, using the fact that Int works but other methods aren't exposed to Objective-C. This is pretty horrible as it stands...

class EnumSupport : NSObject {
    class func textFor(logSeverity severity: LogSeverity) -> String {
        return severity.text()
    }
}

@objc public enum LogSeverity: Int {
    case Debug
    case Info
    case Warn
    case Error

    func text() -> String {
        switch self {
            case .Debug: return "debug"
            case .Info: return "info"
            case .Warn: return "warn"
            case .Error: return "error"
        }
    }
}

edited Jan 25, 2017 at 22:27

shim

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answered Nov 30, 2016 at 23:21

Dan Rosenstark

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Comments

Chris Garrett · Accepted Answer · 2018-05-18 18:29:32Z

4

This is my use case:

I avoid hard-coded Strings whenever I can, so that I get compile warnings when I change something
I have a fixed list of String values coming from a back end, which can also be nil

Here's my solution that involves no hard-coded Strings at all, supports missing values, and can be used elegantly in both Swift and Obj-C:

@objc enum InventoryItemType: Int {
    private enum StringInventoryItemType: String {
        case vial
        case syringe
        case crystalloid
        case bloodProduct
        case supplies
    }

    case vial
    case syringe
    case crystalloid
    case bloodProduct
    case supplies
    case unknown

    static func fromString(_ string: String?) -> InventoryItemType {
        guard let string = string else {
            return .unknown
        }
        guard let stringType = StringInventoryItemType(rawValue: string) else {
            return .unknown
        }
        switch stringType {
        case .vial:
            return .vial
        case .syringe:
            return .syringe
        case .crystalloid:
            return .crystalloid
        case .bloodProduct:
            return .bloodProduct
        case .supplies:
            return .supplies
        }
    }

    var stringValue: String? {
        switch self {
        case .vial:
            return StringInventoryItemType.vial.rawValue
        case .syringe:
            return StringInventoryItemType.syringe.rawValue
        case .crystalloid:
            return StringInventoryItemType.crystalloid.rawValue
        case .bloodProduct:
            return StringInventoryItemType.bloodProduct.rawValue
        case .supplies:
            return StringInventoryItemType.supplies.rawValue
        case .unknown:
            return nil
        }
    }
}

answered May 18, 2018 at 18:29

Chris Garrett

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4 Comments

agirault Over a year ago

I cannot use [InventoryItemType fromString:] from objective-c: it gives the error "Receiver type 'InventoryItemType' is not an Objective-C class"

Chris Garrett Over a year ago

That's because in Objective-C InventoryItemType will be of type Int or NSInteger, it's not a class.

Dragisa Dragisic Over a year ago

Hi @ChrisGarrett I got enum like:

public enum TrackingValue { case constant(String) case customVariable(name: String) case defaultVariable(DefaultVariable) public enum DefaultVariable { case advertisingId case advertisingTrackingEnabled case appVersion case connectionType case interfaceOrientation case isFirstEventAfterAppUpdate case requestQueueSize case adClearId } }

what will be best way to make it to be seen as ObjC enum? Thanks in advance!

Krzysztof Skrzynecki Over a year ago

@agirault you can wrap it in another class, e.g.

class InventoryItemTypeParser: NSObject {     @objc static func fromString(_ string: String?) -> InventoryItemType     {         return InventoryItemType.fromString(string)     } }

Chris Prince · Accepted Answer · 2016-05-06 20:50:17Z

Here's what I came up with. In my case, this enum was in the context providing info for a specific class, ServiceProvider.

class ServiceProvider {
    @objc enum FieldName : Int {
        case CITY
        case LATITUDE
        case LONGITUDE
        case NAME
        case GRADE
        case POSTAL_CODE
        case STATE
        case REVIEW_COUNT
        case COORDINATES

        var string: String {
            return ServiceProvider.FieldNameToString(self)
        }
    }

    class func FieldNameToString(fieldName:FieldName) -> String {
        switch fieldName {
        case .CITY:         return "city"
        case .LATITUDE:     return "latitude"
        case .LONGITUDE:    return "longitude"
        case .NAME:         return "name"
        case .GRADE:        return "overallGrade"
        case .POSTAL_CODE:  return "postalCode"
        case .STATE:        return "state"
        case .REVIEW_COUNT: return "reviewCount"
        case .COORDINATES:  return "coordinates"
        }
    }
}

From Swift, you can use .string on an enum (similar to .rawValue). From Objective-C, you can use [ServiceProvider FieldNameToString:enumValue];

Pawel Jurczyk · Accepted Answer · 2018-03-19 15:25:25Z

You can create an private Inner enum. The implementation is a bit repeatable, but clear and easy. 1 line rawValue, 2 lines init, which always look the same. The Inner has a method returning the "outer" equivalent, and vice-versa.

Has the added benefit that you can directly map the enum case to a String, unlike other answers here.

Please feel welcome to build on this answer if you know how to solve the repeatability problem with templates, I don't have time to mingle with it right now.

@objc enum MyEnum: NSInteger, RawRepresentable, Equatable {
    case
    option1,
    option2,
    option3

    // MARK: RawRepresentable

    var rawValue: String {
        return toInner().rawValue
    }

    init?(rawValue: String) {
        guard let value = Inner(rawValue: rawValue)?.toOuter() else { return nil }
        self = value
    }

    // MARK: Obj-C support

    private func toInner() -> Inner {
        switch self {
        case .option1: return .option1
        case .option3: return .option3
        case .option2: return .option2
        }
    }

    private enum Inner: String {
        case
        option1 = "option_1",
        option2 = "option_2",
        option3 = "option_3"

        func toOuter() -> MyEnum {
            switch self {
            case .option1: return .option1
            case .option3: return .option3
            case .option2: return .option2
            }
        }
    }
}

Jafar Khoshtabiat · Accepted Answer · 2020-02-18 06:55:19Z

1

I think @Remi 's answer crashes in some situations as I had this:

My error's screesshot. so I post my edition for @Remi 's answer:

@objc public enum LogSeverity: Int, RawRepresentable {
    case debug
    case info
    case warn
    case error

    public typealias RawValue = String

    public var rawValue: RawValue {
        switch self {
            case .debug:
                return "DEBUG"
            case .info:
                return "INFO"
            case .warn:
                return "WARN"
            case .error:
                return "ERROR"
        }
    }

    public init?(rawValue: RawValue) {
        switch rawValue {
            case "DEBUG":
                self = .debug
            case "INFO":
                self = .info
            case "WARN":
                self = .warn
            case "ERROR":
                self = .error
            default:
                return nil
        }
    }
}

edited Feb 18, 2020 at 6:55

answered Feb 8, 2020 at 4:19

Jafar Khoshtabiat

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2 Comments

Retro Over a year ago

is there any way to create this enum from Objc, when I try [LogSeverity rawValue:] it doesn't find initializer.

OliverD Over a year ago

How can I access the string value from objective c?

Sound Blaster · Accepted Answer · 2024-08-13 16:49:32Z

A working solution based on the answer provided by @Remi-Cilia at https://stackoverflow.com/a/38490781/602249, for using string values in Objective-C:

@objcMembers public final class VideoTypeToString: NSObject {
    public static func rawValue(of target: VideoType) -> String? {
        target.rawValue
    }
}


@objc public enum VideoType: Int, RawRepresentable {
    case video
    case clip
    case video_message
    case story

    public typealias RawValue = String

    public var rawValue: RawValue {
        switch self {
            case .video:
                return "video"
            case .clip:
                return "clip"
            case .video_message:
                return "video_message"
            case .story:
                return "story"
        }
    }

    public init?(rawValue: RawValue) {
        switch rawValue {
            case "video":
                self = .video
            case "clip":
                self = .clip
            case "video_message":
                self = .video_message
            case "story":
                self = .story
            default:
                return nil
        }
    }
}

Usage in Objective-C code:

VideoType type = VideoTypeClip;
NSString *stringType = [VideoTypeToString rawValueOf:type];

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