How to use completionHandler Closure with return in Swift?

Question

I am trying to us a RESTful API that returns some json data. I want to encapsulate the code that creates the HTTP Request and sets the headers in its own method so I can call it by entering a url String and then have the method return a JSON object.

In the following snippet of code, I have already created the request object and set the headers, and I call that variable "req". I have not declared any objects named data, response, or error. I have the following code that correctly prints out a JSON object

let sesh = NSURLSession.sharedSession()     let dataTask = sesh.dataTaskWithRequest(req, completionHandler: {(data, response, error) in         var jsonError : NSError?         let jsonBlob = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableLeaves, error: &jsonError)         println(jsonBlob)         });      dataTask.resume() 

So here's my question. How do I make it so that this completionHandler block is able to return the jsonBlob, which is of type "AnyObject!"? If I modify the code slightly to be the following:

let sesh = NSURLSession.sharedSession()     let dataTask = sesh.dataTaskWithRequest(req, completionHandler: {(data, response, error) -> AnyObject! in         var jsonError : NSError?         let jsonBlob : AnyObject! = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableLeaves, error: &jsonError)         return jsonBlob         });      dataTask.resume() 

then the program will not compile as the call to dataTaskWithRequest:completionHandler gives a compiler warning saying:

 Could not find an overload for 'dataTaskWithRequest' that accepts the supplied arguments 

I don't understand this. I'm using the correct syntax for returning closures, as is given in this page of the Swift Docs:

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html

Answer 1

func getSomething(callback: (Array<AnyObject>) -> ()) {     var dataTask = NSURLSessionDataTask()     dataTask = session.dataTaskWithRequest(request) { (data, response, error) in         if (error == nil) {             var callbackArray = Array<MyObject>()             let responseDict = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: nil) as NSDictionary             let response = responseDict.objectForKey("response_key") as NSDictionary             let array = response.objectForKey("array_key") as NSArray              for item: AnyObject in array {                 var arrayItem = MyObject(dict: item as NSDictionary)                 callbackArray.append(arrayItem)             }              callback(callbackArray)         } else {             // handle an error         }     }     dataTask.resume() } 

Then you could do something like:

getSomething() { (response) in     if let responseArray = response as? Array<MyObject> {         self.somethings = responseArray     } }