How to use Swift struct in Objective-C

Question

Simply I have a struct that stores the application constants as below:

struct Constant {

    static let ParseApplicationId = "xxx"
    static let ParseClientKey = "xxx"

    static var AppGreenColor: UIColor {
        return UIColor(hexString: "67B632")
    }
}

These constants can be use in Swift code by calling Constant.ParseClientKey for example. But in my code, it also contains some Objective-C classes. So my question is how to use these constants in the Objective-C code?

If this way to declare constants is not good then what is the best way to create global constants to be used in both Swift and Objective-C code?

Answer 1

Sad to say, you can not expose struct, nor global variables to Objective-C. see the documentation.

As of now, IMHO, the best way is something like this:

let ParseApplicationId = "xxx"
let ParseClientKey = "xxx"
let AppGreenColor = UIColor(red: 0.2, green: 0.7, blue: 0.3 alpha: 1.0)

@objc class Constant: NSObject {
    private init() {}

    class func parseApplicationId() -> String { return ParseApplicationId }
    class func parseClientKey() -> String { return ParseClientKey }
    class func appGreenColor() -> UIColor { return AppGreenColor }
}

In Objective-C, you can use them like this:

NSString *appklicationId = [Constant parseApplicationId];
NSString *clientKey = [Constant parseClientKey];
UIColor *greenColor = [Constant appGreenColor];