问题
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?
回答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.
回答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 Swift and Objective-C.
@objc public enum LogSeverity: Int, RawRepresentable {
case debug
case info
case warn
case error
struct Constants {
static let routes: [LogSeverity: String] = [
.debug: "DEBUG",
.info: "INFO",
.warn: "WARN",
.error: "ERROR"
]
}
public typealias RawValue = String
public var rawValue: RawValue {
guard let value = Constants.routes[self] else {
fatalError("constants definition is missing: \(self)")
}
return value
}
public init?(rawValue: RawValue) {
guard let severity = Constants.routes.first(where: { $0.value == rawValue }) else {
return nil
}
self = severity.key
}
}
回答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"
}
}
}
回答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]
回答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
回答6:
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"
}
}
}
回答7:
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
}
}
}
回答8:
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];
回答9:
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
}
}
}
}
来源：https://stackoverflow.com/questions/30480338/how-to-make-a-swift-string-enum-available-in-objective-c