URLSession Lack of Retain Cycle Example

URLSessionRetainCycle.swift

import Foundation

class ViewController{
    var networking = URLSession.shared
    var isLoading = false
    
    func loadImages() {
        print("loading images")
        networking.dataTask(with: URL(string: "https://deckofcardsapi.com/api/deck/new/draw/?count=52")!) { (_, _, _) in
            print("Load Complete")
            self.isLoading = true
        }.resume() //Remove this and ViewController won't deallocate because the completionHandler keeps it alive
    }
    
    deinit {
        print("ViewController Deallocated")
    }
}

var viewController: ViewController? = ViewController()
viewController?.loadImages()
viewController = nil

// No Retain Cycle
// dataTask.completionHandler -> ViewController -> URLSession -> URLSessionDataTask

// However the ViewController will be kept in memory as long as the completionHandler is kept in memory so it won't deallocate if the completionHandler is never called (i.e. we don't resume the data task)

// If we use weak self the ViewController will be dismissed immediately when we set it to nil without waiting for the dataTask CompletionHandler to be called and deallocated