NSURLSessionDataTask: func接收但不返回数据

Question

我尝试创建一个简单的函数，它接收URL并简单地返回网页的HTML。NSURLSessionDataTask本身似乎工作正常，当我println(data)时，我可以看到整个html。但是func只返回初始值"#!?“。我怀疑DataTask是异步的吗？

我该怎么处理呢？

    func loadHTML(targetURL: String) -> String {

    var theTargetURL = NSURL(string:targetURL)
    var theResult = "#!?"

    var request: NSURLRequest = NSURLRequest(URL:theTargetURL)
    let config = NSURLSessionConfiguration.defaultSessionConfiguration()
    let session = NSURLSession(configuration: config)

    let task : NSURLSessionDataTask = session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
        println(NSString(data: data, encoding: NSASCIIStringEncoding))

        if error != nil {
            println(error.localizedDescription)
            theResult = "error"
        }
        if data != nil {
            theResult = NSString(data: data, encoding: NSASCIIStringEncoding)
            println("RECEIVED\t\t\(countElements(theResult)) CHARS")
        }
    });
    task.resume()

    return theResult
}

Answer 1

下面是一个示例，您将如何使用完成处理程序来完成它。

 typealias CompletionBlock = (NSData!, NSURLResponse!, NSError!) -> Void

  func loadHtml(targetUrlString: String, completion: CompletionBlock){

    let targetUrl = NSURL(string: targetUrlString)
    let request = NSURLRequest(URL: targetUrl)

    let session = NSURLSession.sharedSession()
    let task = session.dataTaskWithRequest(request, completionHandler: completion)
    task.resume()

  }

然后，从你需要的方法中调用它，

func viewDidLoad(){
  super.viewDidLoad()
  loadHtml("http://google.com", completion: { (responseData: NSData!, response: NSURLResponse!, error: NSError!) -> Void in

    if responseData != nil{

      let resultString = NSString(data: responseData, encoding: NSASCIIStringEncoding)
      println(resultString)

      /* 
        do some task or update on the main thread
        dispatch_async(dispatch_get_main_queue){
          myActivityIndicator.stopAnimating()
        }
      */

    }else if error != nil{

      println("Error occurred: \(error.localizedDescription)")

    }

  })