swift - fatal error : unexpectedly found nil while unwrapping an Optional value with URLSession

Question

我有一个在 Swift 2.2 中工作的方法，但是自从我将我的代码转换为 Swift 3 之后它就不再工作了，这个方法的作用是将用户名和密码登录到具有 Windows 身份验证的 URL，如果信用是正确则返回真，不正确则返回假。

方法如下:

func loginUser(_ username: String, password: String, completion: @escaping (_ result: Bool) -> Void)
    {
        //Setup the NSURLSessionConfiguration

        let configuration = URLSessionConfiguration.default

        //Setup the NSURLSession

        let session = Foundation.URLSession(configuration: configuration, delegate: self, delegateQueue: nil)

        //Add the username and password to NSURLCredential

        credential = URLCredential(user:username, password:password, persistence: .forSession)

        //Create request URL as String

        let requestString = NSString(format:"%@", webservice) as String

        //Convert URL string to NSURL

        let url: URL! = URL(string: requestString)

        //Prepare the task to get data.

        let task = session.dataTask(with: url, completionHandler: {
            data, response, error in

            DispatchQueue.main.async(execute: {

                if(error == nil)
                {

                    //If there is no error calling the API, return true

                    completion(true)
                }
                else
                {

                    //If there is an error calling the API, return false

                    completion(false)
                }

            })

        })

        //Run the task to get data.

        task.resume()

    }

我得到这个错误:

fatal error: unexpectedly found nil while unwrapping an Optional value

这发生在这里:

let task = session.dataTask(with: url, completionHandler: {
            data, response, error in

            DispatchQueue.main.async(execute: {

                if(error == nil)
                {

                    //If there is no error calling the API, return true

                    completion(true)
                }
                else
                {

                    //If there is an error calling the API, return false

                    completion(false)
                }

            })

        })

我做错了什么？

这出现在 fatal error 之前的调试导航器中:

function signature specialization <preserving fragile attribute, Arg[1] = [Closure Propagated : reabstraction thunk helper from @callee_owned (@unowned Swift.UnsafeBufferPointer<Swift.UInt8>) -> () to @callee_owned (@unowned Swift.UnsafeBufferPointer<Swift.UInt8>) -> (@out ()), Argument Types : [@callee_owned (@unowned Swift.UnsafeBufferPointer<Swift.UInt8>) -> ()]> of generic specialization <preserving fragile attribute, ()> of Swift.StaticString.withUTF8Buffer <A> ((Swift.UnsafeBufferPointer<Swift.UInt8>) -> A) -> A

我相信我的问题出在这里:

/**
     Requests credentials from the delegate in response to a session-level authentication request from the remote server.
     */

    func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {

        if challenge.previousFailureCount > 0
        {
            completionHandler(Foundation.URLSession.AuthChallengeDisposition.cancelAuthenticationChallenge, nil)
        }
        else
        {
            completionHandler(Foundation.URLSession.AuthChallengeDisposition.useCredential, URLCredential(trust:challenge.protectionSpace.serverTrust!))
        }

    }

    /**
     Requests credentials from the delegate in response to an authentication request from the remote server.
     */

    func urlSession(_ session: URLSession, task: URLSessionTask, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {

        completionHandler(Foundation.URLSession.AuthChallengeDisposition.useCredential,credential)

    }

它不喜欢这些方法。

Answer 1

更改 URL 声明自

let url: URL! = URL(string: requestString)

到:

let url: URL = URL(string: requestString)!

仅此一项就可以解决问题；否则它会显示您的 requestString 错误。