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, which states in part:

Use Classes When You Need Objective-C Interoperability

If you use an Objective-C API that needs to process your data, or you need to fit your data model into an existing class hierarchy defined in an Objective-C framework, you might need to use classes and class inheritance to model your data. For example, many Objective-C frameworks expose classes that you are expected to subclass.

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];