How to use URLSession delegate with custom class - ios

Question

I'm used to making a custom class for URLSession using singleton. So I'm using it with URLSession delegate first time and I'm getting confused. Because delegate method is not called!
Can I know any solution? Did I miss something?
And I just want to check whether making a custom class for URLSession is a good thing?
Here is my code. This is my custom API for URLSession.
import UIKit
class CustomNetworkAPI {
static let shared = CustomNetworkAPI()
var session: URLSession?
private var sessionDataTask: URLSessionDataTask?
private var sessionDownloadTask: URLSessionDownloadTask?
var cache: URLCache?
private init() {}
func downloadTaskForImage(_ url: URL, _ completionHandler: #escaping (Result<URL, Error>) -> ()) {
// print(session.delegate)
sessionDownloadTask = session?.downloadTask(with: url, completionHandler: { (url, response, error) in
if let error = error {
completionHandler(.failure(error))
return
}
guard let url = url else {
completionHandler(.failure(URLRequestError.dataError))
return
}
completionHandler(.success(url))
})
sessionDownloadTask?.resume()
}
}
And this is sample code(not whole thing) of VC using the api and delegate.
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let api = CustomNetworkAPI.shared
let config = URLSessionConfiguration.default
api.session = URLSession(configuration: config, delegate: self, delegateQueue: nil)
guard let url = URL(string: "...") else { return }
api.downloadTaskForImage(url) { (result) in
switch result {
case .success(let url):
print(url)
case .failure(let error):
print(error)
}
}
}
}
extension ViewController: URLSessionDownloadDelegate {
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
print("down load complete")
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
print("ing")
}
}

Answer 1

I was missing something, which is this quote below that I found in apple docs.
Your URLSession object doesn’t need to have a delegate. If no delegate is assigned, a system-provided delegate is used, and you must provide a completion callback to obtain the data.
So I tried to remove the completion handler block, and the delegate method was called.