swift - 子类 URLSession iOS 10

Question

我正在尝试使用 Xcode 8 在 iOS 10 上对 URLSession 进行子类化。我相信 Swift 类型系统越来越困惑，但我可能遗漏了一些东西:

class MyURLSession: URLSession {

// No errors
override func downloadTask(with request: URLRequest) -> URLSessionDownloadTask {
    return URLSessionDownloadTask()
}

// No errors
override func downloadTask(with url: URL) -> URLSessionDownloadTask {
    return URLSessionDownloadTask()
}

// See errors below
override func downloadTask(with request: URLRequest, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Void) -> URLSessionDownloadTask {
    return URLSessionDownloadTask()
}

// See errors below
override func downloadTask(with url: URL, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Void) -> URLSessionDownloadTask {
    return URLSessionDownloadTask()
}
}



error: method does not override any method from its superclass
    override func downloadTask(with request: URLRequest, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Void) -> URLSessionDownloadTask {
                  ^
Foundation.URLSession:6:15: note: potential overridden instance method 'downloadTask(with:completionHandler:)' here
    open func downloadTask(with request: URLRequest, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Swift.Void) -> URLSessionDownloadTask
              ^
Foundation.URLSession:7:15: note: potential overridden instance method 'downloadTask(with:completionHandler:)' here
    open func downloadTask(with url: URL, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Swift.Void) -> URLSessionDownloadTask
              ^
/Users/pshah/Networking/Webservice.swift:108:19: error: method does not override any method from its superclass
    override func downloadTask(with url: URL, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Void) -> URLSessionDownloadTask {
                  ^
Foundation.URLSession:6:15: note: potential overridden instance method 'downloadTask(with:completionHandler:)' here
    open func downloadTask(with request: URLRequest, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Swift.Void) -> URLSessionDownloadTask
              ^
Foundation.URLSession:7:15: note: potential overridden instance method 'downloadTask(with:completionHandler:)' here
    open func downloadTask(with url: URL, completionHandler: @escaping (URL?, URLResponse?, Error?) -> Swift.Void) -> URLSessionDownloadTask
              ^

Answer 1

我想通了。我的项目中有一个 Error，所以必须在有错误的方法中将 Error? 限定为 Swift.Error?。