Callback syntax in swift 3 - swift

Question

I am trying to create a callback on swift 3 but haven't had any luck so far. I was taking a look at this question: link which is similar, but the answer gives me an error.
Basically I have an API struct with a static function that I need to have a callback.
import UIKit
struct API {
public static func functionWithCallback(params: Dictionary<String, String>, success: #escaping ((_ response: String) -> Ticket), failure: #escaping((_ error:String) -> String) ) {
let app_server_url = "http://api.com" + params["key"]!
let url: URL = URL(string: app_server_url)!
var request: URLRequest = URLRequest(url: url)
request.httpMethod = "POST"
do {
request.httpBody = try JSONSerialization.data(withJSONObject: params, options: .prettyPrinted)
} catch let error {
print(error.localizedDescription)
}
request.addValue("application/json charset=utf-8", forHTTPHeaderField: "Content-Type")
request.addValue("application/json charset=utf-8", forHTTPHeaderField: "Accept")
let session = URLSession.shared
let task = session.dataTask(with: request as URLRequest, completionHandler: { data, response, error in
guard error == nil else {
return
}
guard let data = data else {
return
}
DispatchQueue.main.async {
do {
let json = try JSONSerialization.jsonObject(with: data) as! [String: Any]
print(json)
var message = ""
if let result = json["result"] as? String {
if(result == "success") {
//attempt to call callback gives me an error: extra argument in call
success("") {
let ticket = json["ticket"] as! NSDictionary
var date = ticket["date"] as! String
var ticket: Ticket = nil
ticket.setDate(date: date)
return ticket
}
}
else {
message = json["message"] as! String
print(message)
}
} catch let error {
print(error.localizedDescription)
let description = error.localizedDescription
if let data = description.data(using: .utf8) {
do {
let jsonError = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any]
let message = jsonError?["message"] as! String
} catch {
}
}
}
}
})
task.resume()
}
}
So I basically can't call the callback success because it gives me an error: Extra argument in call. Any idea on how to fix it?
My goal is to call:
API.functionWithCallback(params: params, success() -> Ticket {
//do something with the returned ticket here
},
error() -> () {
//do something with the error message here
}
)

Answer 1

I believe you have it wrong on how to use call back closures, from what I can understand of your question you want to do something with the ticket in the call back closure and to do that it should be a parameter of the closure not the return type of the closure.
Replace your function declaration with this:
public static func functionWithCallback(params: Dictionary<String, String>, success: #escaping ((_ response: String, _ ticket: Ticket) -> Void), failure: #escaping((_ error:String) -> Void) ) {
And inside the function replace this:
success("") {
let ticket = json["ticket"] as! NSDictionary
var date = ticket["date"] as! String
var ticket: Ticket = nil // Im not sure what you are trying to do with this line but this will definitely give an error
ticket.setDate(date: date)
return ticket
}
With:
let ticket = json["ticket"] as! NSDictionary
var date = ticket["date"] as! String
var ticket: Ticket = nil // fix this line
ticket.setDate(date: date)
success("",ticket)
And then you can call the function like this:
API.functionWithCallback(params: params, success: { response, ticket in
// you can use ticket here
// and also the response text
}) { errorMessage in
// use the error message here
}

Answer 2

Try this :
func uploadImage(api: String,token : String, methodType : String, requestDictionary: [String:AnyObject],picData:[Data], successHandler: #escaping (AnyObject) -> Void,failureHandler: #escaping (NSError) -> Void)
{
if Common_Methods.Reachability1.isConnectedToNetwork() == false
{
let del :AppDelegate = (UIApplication.shared.delegate as? AppDelegate)!
let nav : UINavigationController = (del.window?.rootViewController as? UINavigationController)!
let alert = UIAlertController(title: "", message: "The Internet connection appears to be offline" , preferredStyle: UIAlertControllerStyle.alert)
// Create the actions
let okAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.default)
{
UIAlertAction in
}
alert.addAction(okAction)
nav.present( alert, animated: true, completion: nil)
return
}
let apiUrl = "\(KbaseUrl)\(api)"
let session = URLSession.shared
let url: NSURL = NSURL(string: apiUrl as String)!
print(url)
let request = NSMutableURLRequest(url: url as URL)
request.httpMethod = methodType
let boundary = NSString(format: "---------------------------14737809831466499882746641449") as String
//-------- add token as perameter and set a check if token not nill then set token in header -------
if(token.characters.count > 0)
{
request.setValue(token, forHTTPHeaderField: "x-logintoken")
}
request.setValue("Keep-Alive", forHTTPHeaderField: "Connection")
request.setValue("multipart/form-data; boundary="+boundary, forHTTPHeaderField: "Content-Type")
let data = createBodyWithParameters(parameters: requestDictionary, filePathKey:nil, imageDataKey: picData.count > 0 ? picData : [], boundary: boundary)
print(data)
request.httpBody = data
let task = session.dataTask(with: request as URLRequest) { data, response, error in
// handle fundamental network errors (e.g. no connectivity)
guard error == nil && data != nil else {
successHandler(data as AnyObject )//completion(data as AnyObject?, error as NSError?)
print(error)
DispatchQueue.main.async {
Common_Methods.hideHUD(view: (topVC?.view)!)
}
return
}
// check that http status code was 200
if let httpResponse = response as? HTTPURLResponse , httpResponse.statusCode != 200 {
do {
let responseObject = try JSONSerialization.jsonObject(with: data!, options: []) as? NSDictionary
if let responseDictionary = responseObject as? [String:AnyObject]
{
if responseDictionary["statusCode"] as! Int == 401
{
// self.objDelegate.sessionExpire(msgStr: "Session Expired. Please login again to continue.")
}
else
{
//completion(String(data: data!, encoding: String.Encoding.utf8) as AnyObject?, nil)
}
}
} catch let error as NSError {
print(error)
DispatchQueue.main.async {
Common_Methods.hideHUD(view: (topVC?.view)!)
}
// completion(String(data: data!, encoding: String.Encoding.utf8) as AnyObject?, nil)
}
}
// parse the JSON response
do {
DispatchQueue.main.async {
Common_Methods.hideHUD(view: (topVC?.view)!)
}
let responseObject = try JSONSerialization.jsonObject(with: data!, options: []) as? NSDictionary
successHandler(responseObject! )
} catch let error as NSError {
DispatchQueue.main.async {
Common_Methods.hideHUD(view: (topVC?.view)!)
}
// completion(String(data: data!, encoding: String.Encoding.utf8) as AnyObject?, error)
failureHandler(error)
}
}
task.resume()
// return task
}
and function Call is :
WebService.sharedInstance.uploadImage(api: KEditEmployerProfile,token: token,methodType: "PUT", requestDictionary: parameters1 as! [String : AnyObject], picData: [imageData as Data], successHandler: { (responseObject) in
print(responseObject)
}) { (error) in
print(error)
}
}