I'm creating a basic application in swift where I get data from an api and show it. My Model class handles the fetching data part and I use a delegate to communicate data with the ViewController.
However when fetched data is passed into the controller it is nill for some reason. Here are the things I know/have tried.
Abstracted code is below.
//Model Class
protocol DataDetailDelegate {
func datadetailFetched(_ datadetail: DataDetailItem)
}
class Model {
var datadetaildelegate: DataDetailDelegate?
func fetchData(ID: String) {
let url = URL(string: Constants.Data_URL + ID)
guard url != nil else {
print("Invalid URL!")
return
}
let session = URLSession.shared.dataTask(with: url!) { data, response, error in
if error != nil && data == nil {
print("There was a data retriving error!")
return
}
let decoder = JSONDecoder()
do {
let response = try decoder.decode(MealDetail.self, from: data!)
if response != nil {
DispatchQueue.main.async {
self.datadetaildelegate?.datadetailFetched(response)
}
}
} catch {
print(error.localizedDescription)
}
}
session.resume()
}
}
//View Controller
import UIKit
class DetailViewController: UIViewController, DataDetailDelegate {
@IBOutlet weak var instruction: UITextView!
var model = Model()
var datadetail : DataDetailItem?
override func viewDidLoad() {
super.viewDidLoad()
model.datadetaildelegate = self
model.fetchData(ID: data.id)
if self.datadetail == nil {
print("No data detail available")
return
}
self.instruction.text = datadetail.instruction
}
func datadetailFetched(_ datadetail: DataDetailItem) {
self.datadetail = datadetail
}
}
As mentioned in the comments, there are many problems with the above code, but the main one being not recognising the asynchronous nature of the fetchData.
The below is a rough solution that addresses the critical issues with your code, rather than being best practice and addressing all of them. For example you could also check the contents of error and response codes, and pass them back through the completion handler (maybe as a Result type).
For starters, streamline your fetchData so that it gets the data and then handles that data via a completion handler in an asynchronous manner. Also, don't call it a Model as it's really not.
class SessionManager {
func fetchData(withID id: String, completion: @escaping (data) -> Void) {
guard let url = URL(string: Constants.Data_URL + ID) else {
print("Invalid URL!")
return
}
let session = URLSession.shared.dataTask(with: url) { data, response, error in
guard error == nil, let data = data else { //could be done far better by checking error and response codes
print("There was a data retriving error!")
return
}
completion(data)
}
session.resume()
}
Then adapt your view conroller so that it creates the session manager and fetches the data, but processes it in the completion handler. I've only added the relevant content.
class DetailViewController: UIViewController, DataDetailDelegate {
lazy var sessionManager = SessionManager()
var datadetail : DataDetailItem?
override func viewDidLoad() {
super.viewDidLoad()
sessionManager.fetchData(withID: data.id){ [weak self] data in
let decoder = JSONDecoder()
do {
let response = try decoder.decode(MealDetail.self, from: data)
DispatchQueue.main.async {
self?.datadetail = response
self?.instruction.text = datadetail.instruction
}
} catch {
print(error.localizedDescription)
}
}
}
// rest of view controller
}
That should be enough to get you going. There are many best practice examples/tutorials scattered around that would be worth a look so you can refine things further.
Note: this has been written in here without a compiler to hand, so there may be some syntax that needs tweaking.