I'm struggling to understand why the async-await version of URLSession download task APIs do not call the delegate functions, whereas the old non-async version that returns a reference to the download task works just fine.
Here is my sample code:
class DownloadDelegate: NSObject, URLSessionDownloadDelegate {
func urlSession(_ session: URLSession,
downloadTask: URLSessionDownloadTask,
didWriteData bytesWritten: Int64,
totalBytesWritten: Int64,
totalBytesExpectedToWrite: Int64) {
// This only prints the percentage of the download progress.
let calculatedProgress = Float(totalBytesWritten) / Float(totalBytesExpectedToWrite)
let formatter = NumberFormatter()
formatter.numberStyle = .percent
print(formatter.string(from: NSNumber(value: calculatedProgress))!)
}
}
// Here's the VC.
final class DownloadsViewController: UIViewController {
private let url = URL(string: "https://pixabay.com/get/g0b9fa2936ff6a5078ea607398665e8151fc0c10df7db5c093e543314b883755ecd43eda2b7b5178a7e613a35541be6486885fb4a55d0777ba949aedccc807d8c_1280.jpg")!
private let delegate = DownloadDelegate()
private lazy var session = URLSession(configuration: .default, delegate: delegate, delegateQueue: nil)
// for the async-await version
private var task: Task<Void, Never>?
// for the old version
private var downloadTask: URLSessionDownloadTask?
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
task?.cancel()
task = nil
task = Task {
let (_, _) = try! await session.download(for: URLRequest(url: url))
self.task = nil
}
// If I uncomment this, the progress listener delegate function above is called.
// downloadTask?.cancel()
// downloadTask = nil
// downloadTask = session.downloadTask(with: URLRequest(url: url))
// downloadTask?.resume()
}
}
What am I missing here?
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