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?

Solution 1

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.

Solution 2

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
        }
    }
}

Solution 3

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"
        }
    }
}

Solution 4

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]

Solution 5

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 the "Interacting with C APIs" of the Using Swift with Cocoa and Objective-C documentation

View more solutions

Comments

[Stephen Paul]

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

[David]

@StephenPaul Something like ConnectivityStatusWifi. If you type that in you should see Xcode try to autocomplete.

[Cameron Askew]

@David but you cannot call name() in objc

[i89]

I think you should make declare the function as public

[Chris Prince]

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

[Gobe]

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.

[Zeeshan]

property define in swift as > public var webViewType : WebViewType? is not found when i try to set it in OBJC class > webViewController.webViewType = WebViewType.TermsOfUse

[Zack Shapiro]

Page cannot be found on link

[Hendrix]

This worked for me with some minor alterations. @objcMembers public class LogSeverityBridge: NSObject { static func debug() -> String { return TravelerProtectionLevel.premium.rawValue }

[Priyal]

@Chuck even public function will not expose the method.

[gaussblurinc]

@Remy Cilia does it work in latest swift 4.1? I don't see any related symbols except typealias Swift_Enum in ProductModule-Swift.h generated header.

[agirault]

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

[Daniel Sanchez]

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

[Gobe]

@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 })

[Chris Garrett]

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

[Tom Kraina]

This is exactly the approach I was looking for!

[Dragisa Dragisic]

@David I got enum 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!

[Dragisa Dragisic]

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!

[Dragisa Dragisic]

What if we have associated values in enum? What is the best approach to make it available at Objective C?

[beowulf]

I am getting error Type 'LogSeverity.Constants' has no member 'routes'

[Jafar Khoshtabiat]

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

[Krzysztof Skrzynecki]

@agirault you can wrap it in another class, e.g. class InventoryItemTypeParser: NSObject { @objc static func fromString(_ string: String?) -> InventoryItemType { return InventoryItemType.fromString(string) } }

[Vladimirs Matusevics]

@JafarKhoshtabiat switch is the keyword, not swift

[Jafar Khoshtabiat]

@VladimirsMatusevics I fixed it and requested for edit, tnx for correction

[strangetimes]

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

[Retro]

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

[OliverD]

How can I access the string value from objective c?

[guru]

Yes i also can also not call from objc

[Itachi]

I'm confused a little: after generating LogSeverity enum into swift.h header file, how to access the rawValue by enum case in objc code? There is not enum method concept in objc side, right?

[Aaban Tariq Murtaza]

@Itachi, any solution found?

[Aaban Tariq Murtaza]

rawValue isn't accessible in objc.