How can I call a function from scene delegate which downloads an URL in a view controller?

Question

I am downloading an image in my view controller. I want to update my image every time the app enters the foreground. I tried to call the function to download the image from the scene delegate, but unfortunately, I get the error "Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value", when I try that.

This is my code to download the image which works fine except when I call it from the scene delegate.

        let urlSession = URLSession(configuration: .default)

        let url = URL(string: "https://jarisstoriesphotographyphoto.files.wordpress.com/2020/06/menu1.png")!

        // Create Data Task

        let dataTask = urlSession.dataTask(with: url) { [weak self] (data, _, error) in
            if let error = error {
                print(error)
            }
            if let data = data {
                DispatchQueue.main.async {
                    // Create Image and Update Image View
                    // self?.imageView.image
                    self?.imageView.image = UIImage(data: data)
                }
            }
        }
        // Start Data Task
        dataTask.resume()

This is the code I used in my scene delegate. I also tried to call the download function in the "willConnectTo" but that gave me the same error.

let viewController = ViewController()

func sceneWillEnterForeground(_ scene: UIScene) {
     viewController.downloadImage()
}

Help is very appreciated.

score 0 · Accepted Answer · answered Jun 18 '20 at 08:54

If you want to start a download task every time the app enters foreground, within a view controller then you should do the task in viewWillAppear of the view controller. Here's an example:

class ViewController: UIViewController {
    // ...
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        let urlSession = URLSession(configuration: .default)
         let url = URL(string: "https://jarisstoriesphotographyphoto.files.wordpress.com/2020/06/menu1.png")!

         // Create Data Task

         let dataTask = urlSession.dataTask(with: url) { [weak self] (data, _, error) in
             if let error = error {
                 print(error)
             }
             if let data = data {
                 DispatchQueue.main.async {
                     // Create Image and Update Image View
                     // self?.imageView.image
                     self?.imageView.image = UIImage(data: data)
                 }
             }
         }
         // Start Data Task
         dataTask.resume()
    }
}

How can I call a function from scene delegate which downloads an URL in a view controller?

1 Answers1