Problems trying to port an Objective C completion block into Swift

Question

I'm using a third party library written in objective C with the following method:

- (void)manageServerResponse:(NSURLResponse*)response NSData:(NSData*)data andNSError:(NSError*)error onComplete:(void (^)(NSInteger kindOfError, NSDictionary*jsonResponse))onComplete;

when I port it to swift I do the following:

typealias ResponseCompletedBlock = (NSInteger, NSDictionary?) -> Void
...
let completedResponseMethod : ResponseCompletedBlock = {(kindOfError: NSInteger, jsonResponse: NSDictionary?) -> Void in
    self.onComplete(kindOfError, jsonResponse: jsonResponse)}

let responseManager: ResponseManager = ResponseManager.sharedResponseManager() as! ResponseManager
responseManager.manageServerResponse(response, 
    NSData: data, 
    andNSError: error, 
    onComplete: completedResponseMethod)

I'm getting this error:

Cannot invoke 'manageServerResponse' with an argument list of type '(NSURLResponse?, NSData: NSData?, andNSError: NSError?, onComplete: ResponseCompletedBlock)'

and if I replace the last sentence for

responseManager.manageServerResponse(response, 
    NSData: data, 
    andNSError: error, 
    onComplete: nil)

everything works, so I assume that the problem is with the block structure, but I've tried to change everything and the error remains.

Can you help?

Answer 1

NSDictionary * is mapped to Swift as [NSObject : AnyObject]!, therefore the type of the response block should be

typealias ResponseCompletedBlock = (Int, [NSObject : AnyObject]!) -> Void

and consequently

let completedResponseMethod = {(kindOfError: Int, jsonResponse: [NSObject : AnyObject]!) -> Void in
    // ...
}

One method to figure out the correct Swift signature of functions is to use the autocompletion in Xcode: You start typing

 responseManager.manageServerResponse(

and Xcode suggests

Answer 2

Per Apple docs:

When you bridge from an NSDictionary object to a Swift dictionary, the resulting dictionary is of type [NSObject: AnyObject].

Also, unless the Objective-C code is annotated for nullability, the Swift dictionary is an implicitly-unwrapped optional. Therefore your typealias should look like this:

typealias ResponseCompletedBlock = (NSInteger, [NSObject : AnyObject]!) -> Void

I'd also recommend changing the NSInteger to Int.

Answer 3

Is the typealias and completedResponseMethod absolutely necessary for your program to function? If not, this would probably solve your problem:

responseManager.manageServerResponse(response, NSData: data, andNSError: error, onComplete: { 
    $0, $1 in
    self.onComplete($0, jsonResponse: $1)
}

As your error suggests, the error was due to a type mismatch. If you use the default local parameters, you'll be able to work around that particular problem.