未调用 URLSessionDelegate 方法

Question

首先，我已经检查了类似的现有问题，none 个答案适用。
NSURLSession delegates not called
URLSessionDelegate Function Not Being Called

我正在尝试使用 URLSessionDownloadTask 下载文件，就像这样

class MyNetworkManager : NSObject
{
    static let instance = MyNetworkManager()

    var downloadSession : URLSession?

    init()
    {
        super.init()

        let downloadConfiguration = URLSessionConfiguration.default
        downloadSession = URLSession(configuration: downloadConfiguration, delegate: self, delegateQueue: nil)
    }

    func download(_ url : URL)
    {
        var urlRequest = URLRequest(url: url)
        urlRequest.httpMethod = "GET"
        let downloadTask = downloadSession?.downloadTask(with: urlRequest)

        downloadTask?.resume()
    }
}

extension MyNetworkManager : URLSessionDelegate
{
    func urlSession(_ session: URLSession,
                    downloadTask: URLSessionDownloadTask,
                    didWriteData bytesWritten: Int64,
                    totalBytesWritten: Int64,
                    totalBytesExpectedToWrite: Int64)
    {
        // 
    }

    func urlSession(_ session: URLSession,
                    downloadTask: URLSessionDownloadTask,
                    didFinishDownloadingTo location: URL)
    {
        //
    }

    func urlSession(_ session: URLSession,
                    task: URLSessionTask,
                    didCompleteWithError error: Error?)
    {
        //
    }
}

但是，没有 URLSessionDelegate 方法被调用。

通常情况下，如果您使用完成处理程序创建任务，则不会调用委托方法 - 事实并非如此，我在创建任务时仅使用 URLRequest 作为参数。

Session 的 delegate 设置正确，调用 downloadTask?.resume() 后其 state 属性为 running

MyNetworkManager是单例，我是这样用的

MyNetworkManager.instance.download(someURL)

所以肯定保留了一个实例。

我是不是漏掉了什么？

Answer 1

您必须遵守相关协议，例如：

extension MyNetworkManager: URLSessionDelegate {
    // this is intentionally blank

    // obviously, if you implement any delegate methods for this protocol, put them here
}

extension MyNetworkManager: URLSessionDownloadDelegate {
    func urlSession(_ session: URLSession,
                    downloadTask: URLSessionDownloadTask,
                    didWriteData bytesWritten: Int64,
                    totalBytesWritten: Int64,
                    totalBytesExpectedToWrite: Int64) {
        print(#function)
    }

    func urlSession(_ session: URLSession,
                    downloadTask: URLSessionDownloadTask,
                    didFinishDownloadingTo location: URL) {
        print(#function)
    }
}

extension MyNetworkManager: URLSessionTaskDelegate {
    func urlSession(_ session: URLSession,
                    task: URLSessionTask,
                    didCompleteWithError error: Error?) {
        print(#function, error ?? "No error")
    }
}

如果你不符合URLSessionDownloadDelegate，它不会调用URLSessionDownloadDelegate方法。

未调用 URLSessionDelegate 方法

URLSessionDelegate methods not called

swift

urlsession