子類URLSession iOS的10

Question

我想使用的Xcode 8.我相信斯威夫特的類型系統是越來越糊塗子類在iOS上10 URLSession，但我可能失去了一些東西：

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。我的項目中有一個Error，因此必須在有錯誤的方法中限定Error?爲Swift.Error?。