Implementing an Objective-C protocol in Swift

Question

I have a protocol that's defined in Objective-C, like:

@protocol MyProtocol <NSObject>
- (void)doStuffWithDictionary:(NSDictionary*)dict 
                    andString:(NSString*)str1
            andOptionalString:(NSString*)str2
             andOptionalArray:(NSArray*)arr
                     callback:(void (^)(id result))onSuccess;
@end

...and I'm trying to define a class in Swift that implements this protocol, like:

class MyImpl : Operation, MyProtocol {
    func doStuff(withDictionary dict: [AnyHashable : Any]!, 
                      andString str1: String!, 
              andOptionalString str2: String? = nil, 
                andOptionalArray arr: NSArray? = nil, 
                  callback onSuccess: ((Any?) -> Void)! {
        ...
    }
}

However I'm getting build errors along the lines of:

Type 'MyImpl' does not conform to protocol 'MyProtocol'
note: candidate has non-matching type '([AnyHashable : Any]!, String!, String?, NSArray?, ((Any?) -> Void)!'
    func doStuff(withDictionary dict: [AnyHashable : Any]!, andString str1: String!, andOptionalString str2: String? = nil, andOptionalArray arr: NSArray? = nil, callback onSuccess: ((Any?) -> Void)!

It appears to be upset about the andOptionalArray arr: NSArray? = nil andOptionalArray arr: NSArray? = nil parameter. What is the correct syntax to use here?

Answer 1

I put your protocol in a project and imported it in <ProjectName>-Bridging-Header.h , and Auto Complete suggested this syntax:

public func doStuff(with dict: [AnyHashable : Any],
               andString str1: String,
       andOptionalString str2: String,
         andOptionalArray arr: [Any],
           callback onSuccess: @escaping (Any) -> Void) {
}

If you want the String and [Any] to be imported as optional, you need to mark them as nullable in Objective-C:

@protocol MyProtocol <NSObject>
- (void)doStuffWithDictionary:(NSDictionary*)dict
                    andString:(NSString*)str1
            andOptionalString:(nullable NSString*)str2
             andOptionalArray:(nullable NSArray*)arr
                     callback:(void (^)(id result))onSuccess;
@end

---

As @MartinR suggested in the comments:

Go to the header file where the protocol is defined, and choose "Generated Interface" from the "Related Items" popup in the top-left corner. That will show you the exact Swift method signature that you have to implement.

This works too and offers different interfaces for different versions of Swift.