Assign Data using Grand Central Dispatch Swift 3 - ios

Question

I created a Networking file for downloading data, and I want to assign the data to another view controller so I can populate a map with annotations. The data download successfully, but I can't get it to assign to the view controller. I can only get it working when I include the networking code in the view controller and use DispatchQueue.main.async. I want to keep the networking file and view controller separate. Any insights would be greatly appreciated. Apologies in advance for the many lines of code.
The networking file is as follows:
import UIKit
class Networking {
static let shared = Networking()
var objects = [Any]()
func getData (_ completionHandler:#escaping (Location?) -> ()) {
//Create the url with NSURL reuqest
let url = URL(string: "http://localhost:3000/locations")
let request = NSMutableURLRequest(url: url! as URL)
//Set HTTP method as GET
request.httpMethod = "GET"
//HTTP Headers
request.addValue("application/json", forHTTPHeaderField: "Accept")
//Create dataTask using the session object to send data to the server
URLSession.shared.dataTask(with: request as URLRequest) { data, response, error in
guard let data = data,
let dataStore = String(data: data, encoding: String.Encoding.utf8) else {
print("Could not find network")
completionHandler(nil)
return
}
guard error == nil else {
print("Error calling GET")
completionHandler(nil)
return
}
let HTTPResponse = response as! HTTPURLResponse
let statusCode = HTTPResponse.statusCode
if (statusCode == 200) {
print("Files downloaded successfully. \(dataStore)" )
} else {
completionHandler(nil)
return
}
//Create json object from data
do {
let json = try! JSONSerialization.jsonObject(with: data , options: []) as? [[String: Any]]
let location: [Location] = []
if let array = json {
for i in 0 ..< array.count {
if let data_object = array[i] as? [String: Any] {
if let _id = data_object["_id"] as? String,
let name = data_object["name"] as? String,
let imageID = data_object["imageID"] as? String,
let category = data_object["category"] as? String,
let details = data_object["details"] as? String,
let latitude = data_object["latitude"] as? Double,
let longitude = data_object["longitude"] as? Double {
var dictionary = [_id, name, imageID, category, details, latitude, longitude] as [Any]
dictionary.append(location)
}
}
}
}
}
}.resume()
}
}
The model is as follows:
class Location {
var _id : String
var name : String
var imageID : String
var category : String
var details : String
var latitude : Double
var longitude : Double
init?(_id: String, name: String, imageID: String, category: String, details: String, latitude: Double, longitude: Double) {
self._id = _id
self.name = name
self.imageID = imageID
self.category = category
self.details = details
self.latitude = latitude
self.longitude = longitude
}
}
The view controller is as follows:
class MapViewController: UIViewController, MGLMapViewDelegate, UIGestureRecognizerDelegate {
override func viewDidLoad() {
super.viewDidLoad()
mapView.delegate = self
Networking.shared.getData { (locations) in
}
populateMap()
}
func populateMap (){
let point = MGLPointAnnotation()
for location in locations {
let coordinate = CLLocationCoordinate2D(latitude: location.latitude, longitude: location.longitude )
point.coordinate = coordinate
point.title = location.name
point.subtitle = location.category
self.mapView.addAnnotation(point)
}
}

Answer 1

You are executing completion blocks only in failure cases. Execute the completion block once you have managed to parse the data and pass the array as parameter to closure/block.
import UIKit
class Networking {
static let shared = Networking()
var objects = [Any]()
func getData (_ completionHandler:#escaping ([Location]?) -> ()) {
//Create the url with NSURL reuqest
let url = URL(string: "http://localhost:3000/locations")
let request = NSMutableURLRequest(url: url! as URL)
//Set HTTP method as GET
request.httpMethod = "GET"
//HTTP Headers
request.addValue("application/json", forHTTPHeaderField: "Accept")
//Create dataTask using the session object to send data to the server
URLSession.shared.dataTask(with: request as URLRequest) { data, response, error in
guard let data = data,
let dataStore = String(data: data, encoding: String.Encoding.utf8) else {
print("Could not find network")
completionHandler(nil)
return
}
guard error == nil else {
print("Error calling GET")
completionHandler(nil)
return
}
let HTTPResponse = response as! HTTPURLResponse
let statusCode = HTTPResponse.statusCode
if (statusCode == 200) {
print("Files downloaded successfully. \(dataStore)" )
} else {
completionHandler(nil)
return
}
//Create json object from data
do {
let json = try! JSONSerialization.jsonObject(with: data , options: []) as? [[String: Any]]
let location: [Location] = []
if let array = json {
for i in 0 ..< array.count {
if let data_object = array[i] as? [String: Any] {
if let _id = data_object["_id"] as? String,
let name = data_object["name"] as? String,
let imageID = data_object["imageID"] as? String,
let category = data_object["category"] as? String,
let details = data_object["details"] as? String,
let latitude = data_object["latitude"] as? Double,
let longitude = data_object["longitude"] as? Double {
var dictionary = [_id, name, imageID, category, details, latitude, longitude] as [Any]
dictionary.append(location) //am not sure of what this means test your code
completionHandler(location)
}
}
}
}
}
}.resume()
}
}
Few more mistakes in your code :
Your completion block expects Location as a parameter. but in your code you are creating an array of Locations.
let location: [Location] = []
So I have modified the completion block parameters to return array of locations
In your for loop you are creating
var dictionary = [_id, name, imageID, category, details, latitude, longitude] as [Any]
and appending it to dictionary.append(location) I have no idea what this code is. I believe what u actually trying to do is create a location object from the data and then add it to location array
location.append(your_new_location_object)
Hope it helps