Unexpected non-void return value in void function in request to server iOS Swift 3

Question

I try to make method for request to server contain Background and Main queue. Finally this method should return NSDictionary of my response from the server.

func sendRequest(UrlString urlString:String,MethodString method:String)->(NSDictionary)  {

    DispatchQueue.global(qos: .background).async {
        var request = URLRequest(url: URL(string:urlString)!)
        request.httpMethod = method
        //let postString = "id=13&name=Jack"
        //request.httpBody = postString.data(using: .utf8)
        let task = URLSession.shared.dataTask(with: request) { data, response, error in
            guard let data = data, error == nil else {                                                 // check for fundamental networking error
                print("error=\(error)")
                return
            }

            if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           // check for http errors
                print("statusCode should be 200, but is \(httpStatus.statusCode)")
                print("response = \(response)")
            }

            let responseString = String(data: data, encoding: .utf8)
            print("responseString = \(responseString)")

        DispatchQueue.main.async {

            do {
                let jsonDictionary:NSDictionary = try JSONSerialization.jsonObject(with: data, options: []) as! [String: AnyObject] as NSDictionary

                return jsonDictionary

            } catch {
                //Handle the error
            }

            //return airports
        }

    }

    task.resume()
}  

And now when try to return jsonDictionary in the main queue, it shows me this error:

Unexpected non-void return value in void function

And now I don't know how to fix this problem.
I am using Xcode 8 , iOS8 and Swift 3 .
Please help me.
Thank you.

Answer 1

You have implemented at least two async operations and they are can't return values. For async operations you should use completion handlers like this:

func sendRequest(urlString: String, method: String, completion: @escaping (_ dictionary: NSDictionary?, _ error: Error?) -> Void) {

    DispatchQueue.global(qos: .background).async {
        var request = URLRequest(url: URL(string:urlString)!)
        request.httpMethod = method
        let task = URLSession.shared.dataTask(with: request) { data, response, error in
            guard let data = data, error == nil else {                                                 // check for fundamental networking error
                print("error=\(error)")
                completion(nil, error)
                return
            }

            if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           // check for http errors
                print("statusCode should be 200, but is \(httpStatus.statusCode)")
                print("response = \(response)")
                // make error here and then
                completion(nil, error)
                return
            }

            let responseString = String(data: data, encoding: .utf8)
            print("responseString = \(responseString)")

            DispatchQueue.main.async {
                do {
                    let jsonDictionary:NSDictionary = try JSONSerialization.jsonObject(with: data, options: []) as! [String: Any] as NSDictionary

                    completion(jsonDictionary, nil)

                } catch {
                    completion(nil, error)
                }
            }

        }

        task.resume()
    }
}