Question

我有以下Swift代码，我向网络服务器发送POST请求并接收值。我收到的错误是在第二行到最后一行说＆＃34;使用未解析的标识符＆＃34;

func download_request() -> String {
    let url:NSURL = NSURL(string: "http://url.com/read.php")!
    let session = NSURLSession.sharedSession()

    let request = NSMutableURLRequest(URL: url)
    request.HTTPMethod = "POST"
    request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringCacheData

    let paramString = "data=name"
    request.HTTPBody = paramString.dataUsingEncoding(NSUTF8StringEncoding)

    let task = session.downloadTaskWithRequest(request) {

        (let location, let response, let error) in

        guard let _:NSURL = location, let _:NSURLResponse = response  where error == nil else {
            print("Error")
            return
        }

        let urlContents = try! NSString(contentsOfURL: location!, encoding: NSUTF8StringEncoding)

        guard let _:NSString = urlContents else {
            print("Error")
            return
        }

     }

    task.resume()
    return urlContents
}

我该如何解决此错误？我认为这意味着我不能在let task = session.downloadTaskWithRequest（request）{}之外使用urlContents但是我如何声明变量以便我可以在外面使用它？

Answer 1

尝试在urlContents块之外声明session.downloadTaskWithRequest(request) { }。像这样：

func download_request() -> String? {
    let url:NSURL = NSURL(string: "http://url.com/read.php")!
    let session = NSURLSession.sharedSession()
    var urlContents: NSString?

    let request = NSMutableURLRequest(URL: url)
    request.HTTPMethod = "POST"
    request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringCacheData

    let paramString = "data=name"
    request.HTTPBody = paramString.dataUsingEncoding(NSUTF8StringEncoding)

    let task = session.downloadTaskWithRequest(request) {

        (let location, let response, let error) in

        guard let _:NSURL = location, let _:NSURLResponse = response  where error == nil else {
            print("Error")
            return
        }

        urlContents = try? NSString(contentsOfURL: location!, encoding: NSUTF8StringEncoding)

        guard let _:NSString = urlContents else {
           print("Error")
           return
        }

     }

    task.resume()
    return (urlContents as! String)
}

然后当你需要使用urlContents用if let binding

打开它时

if let contents = download_request() {
    //Use safely unwrapped contents
}

Answer 2

您可以按下面的方式返回optional

func download_request() -> String? {
     var urlContents: String?
     ....
     ....
     let task = session.downloadTaskWithRequest(request) {

        (let location, let response, let error) in
        ...
        ...
        ...
        guard let _:NSURL = location, let _:NSURLResponse = response  where error == nil else {
            print("Error")
            return
        }
       urlContents = try! NSString(contentsOfURL: location!, encoding: NSUTF8StringEncoding) as String
        guard let _:NSString = urlContents else {
            print("Error")
            return
        }
    }
    task.resume()
    return urlContents
}

并调用类似

的方法

 if let request = download_request() {
     //do anything with your request
 }

建议您正确重命名方法，因为您返回的是下载的数据而不是请求。

这不是将下载的数据作为返回方法返回的正确方法，因为操作完成后将调用completionHandler，因此urlContents将为零。因此，创建另一种方法，将String作为输入并在completionHandler downloadTaskWithRequest内调用它

Swift-使用未解析的标识符

2 个答案: