Why delegate object is nil? - ios

Question

I am facing little weird issue with delegate pattern and I couldn't make it work like I expect. I guess I am missing something here but I couldn't figure it out myself.
Here's how my classes are defined,
class NetworkManager {
weak var delegate: DownloaderProtocol?
func downloadFile(downloadUrl: URL ) {
downloadTask(with: downloadUrl).resume()
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
delegate?.downloadCompleted(task: task, error: error)
}
}
class DownloadManager: DownloaderProtocol {
var networkManager: NetworkManager
init(networkManager: NetworkManager) {
self.networkManager = networkManager
}
func downloadMatches(urls: [String]) {
self.networkManager.delegate = self
for(....) {
self.networkManager.downloadFile(url: url)
}
}
func downloadCompleted(task: URLSessionTask, error: Error) {
// Implementation
}
}
class Matches {
var networkManager: NetworkManager
init() {
self.networkManager = NetworkManager()
}
func getMatchSchedules(urls: [String] , completionHandler: #escaping (Result<Data, Error>) -> Void) {
return DownloadManager.downloadMatches(urls: [String])
}
}
What is the issue ?
When the urlSession - didCompleteWithError method is called, I can see that delegate object is nil.
What I have tried ?
If I remove the weak reference of the delegate i.e weak var delegate: DownloaderProtocol? to var delegate: DownloaderProtocol?, then the delegate object is not nil. It works fine.
I even tried to set the delegates in Matches class, but the delegate is still shown as nil
Any help or point out is welcome.

Answer 1

well I recommend this approach since is not all you code that posted in the question but just the relevant one.
class NetworkManager {
weak var delegate: DownloaderProtocol?
func downloadFile(downloadUrl: URL ) {
downloadTask(with: downloadUrl).resume()
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
delegate?.downloadCompleted(task: task, error: error)
}
}
class DownloadManager: DownloaderProtocol {
var networkManager: NetworkManager
init(networkManager: NetworkManager) {
self.networkManager = networkManager
self.networkManager.delegate = self
}
func downloadMatches(urls: [String]) {
for url in urls {
guard let url = URL(string: url) else {return}
self.networkManager.downloadFile(downloadUrl: url)
}
}
func downloadCompleted(task: URLSessionTask, error: Error) {
// Implementation
}
}
class Matches {
var downloadManager: DownloadManager//NetworkManager
init() {
//self.networkManager = NetworkManager()
//self.networkManager.delegate = DownloadManager()
let networkManager = NetworkManager()
self.downloadManager = DownloadManager(networkManager: networkManager)
}
func getMatchSchedules(urls: [String] , completionHandler: #escaping (Result<Data, Error>) -> Void) {
return downloadManager.downloadMatches(urls: ["asadsdad"])
}
}
you need a download manager in matches that have a network manager when you create matches you create the network manger and set to the init of the download manager so you have a delegate set.

Answer 2

You can use callback in place of delegate.
It's much easier approach than delegate.
typealias APIServiceSuccessCallback = ((Any?) -> ())
ViewController A:
//call from A -> B result fire if completionHandler fire in VC B
addCompanyTargetsController.responseCreateBookingObj = { [unowned self] (returnObject) in
if let object = returnObject as? [String:Any] {
if object["success"] as? Bool == true {
self.loadTargetList()//success block
}
}
}
ViewController B:
var responseCreateBookingObj : APIServiceSuccessCallback? //declaration
func completionHandler() { //from where you fire call this method
guard let callBack = self.responseCreateBookingObj else{
return
}
callBack( true as AnyObject)
}