URLSessionTask instance variable vs local variable - who owns the reference? - ios

Question

Please refer to the code snippet below (certain parts not relevant to question are omitted)
In WebService1, dataTask is an instance variable/property whereas in WebService2, dataTask is a local variable inside the function callWebService.
final class WebService1 {
let urlSession = URLSession(configuration: .default)
// 1. data task is a private property of PNWebService here
private var dataTask: URLSessionDataTask?
func callWebService(completion: () -> ()) {
var urlRequest = URLRequest(url: url)
dataTask = urlSession.dataTask(with: urlRequest) {
// task complete
completion()
}
dataTask?.resume()
}
}
final class WebService2 {
let urlSession = URLSession(configuration: .default)
func callWebService(completion: () -> ()) {
var urlRequest = URLRequest(url: url)
// 2. data task is a local variable here
var dataTask = urlSession.dataTask(with: url) {
// task complete
completion()
}
dataTask.resume()
}
}
Clients an call these two services in the usual way:
let ws1 = WebService1()
ws1.callWebService() {
print("1. complete")
}
let ws2 = WebService2()
ws2.callWebService() {
print("2. complete")
}
Q1) Who owns a strong reference to dataTask in WebService2 so that it is not deallocated before the completion handler is called?
Q2) From a client perspective what is the difference at runtime between WebService1 & WebService2?

Answer 1

Are you asking which pattern is correct? Neither. The URLSession owns the data task and manages its memory as soon as you resume it for the first time, so there is no need for you to keep any reference to it, unless you plan to do something else with that reference such as configuring the task further or cancelling the operation later. Generally it is sufficient and quite usual to say
urlSession.dataTask(with:url) { data, resp, err in
// whatever
}.resume()