如何處理與NSURLSession失去互聯網連接？

Question

我使用NSURL從網站上刮取HTML。問題是，如果在NSURL請求期間互聯網斷開，應用程序崩潰。
代碼：

let myUrl = NSURL(string: "http://www.mywebsite.com/page.html") 
let request = NSMutableURLRequest(URL: myUrl!) 
request.HTTPMethod = "POST" 
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { 
    data, response, error in 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { 
     let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding) 
     if error != nil { 
      print("Error: \(error)") 
     } 
     dispatch_async(dispatch_get_main_queue()) { 
      self.testLabel.text = "\(responseString!)" 
     } 
    } 
} 
task.resume() 

我可以檢查與此代碼NSURL連接之前的互聯網連接，但仍存在運行過程中互聯網的切割出的可能性：
代碼NSURL之前互聯網連接檢查：

let myUrl = NSURL(string: "http://www.mywebsite.com/page.html") 
let request = NSMutableURLRequest(URL: myUrl!) 
request.HTTPMethod = "POST" 
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { 
    data, response, error in 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { 
     let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding) 
     if error != nil { 
      print("Error: \(error)") 
     } 
     dispatch_async(dispatch_get_main_queue()) { 
      self.testLabel.text = "\(responseString!)" 
     } 
    } 
} 
task.resume() 

爲了解決這個問題，我已經使用try/catch操作的研究，但我有沒有運氣成功地建設一個那不給我一個錯誤。有沒有辦法在一個巨大的try/catch中包裝整個NSURL操作以捕獲任何錯誤？我想沿着這行的東西，但它不工作：
代碼：

let myUrl = NSURL(string: "http://www.mywebsite.com/page.html") 
let request = NSMutableURLRequest(URL: myUrl!) 
request.HTTPMethod = "POST" 
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { 
     data, response, error in 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { 
    let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding) 
    if error != nil { 
     print("Error: \(error)") 
    } 
    dispatch_async(dispatch_get_main_queue()) { 
     self.testLabel.text = "\(responseString!)" 
    } 
    } 
} 
task.resume() 
} catch { 
    timer.invalidate 
    sendAlert("Error", message: "You are not connected to the internet") 
} 

Answer 1

時，才應強制解開一個變量，如果你知道一個100％是有值存在，否則就會導致您的應用崩潰。如果您需要更多這方面的信息，你應該檢討的The Swift Programming Language guide

可選的鏈接部分用於檢查一個

下面的代碼應該爲你工作。

let myUrl = NSURL(string: "http://www.mywebsite.com/page.html") 
    let request = NSMutableURLRequest(URL: myUrl!) 
    request.HTTPMethod = "POST" 
    let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { 
     data, response, error in 
     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { 

      if let responseData = data { 

       let responseString = NSString(data: responseData, encoding: NSUTF8StringEncoding) 
       if error != nil { 
        print("Error: \(error)") 
       } 
       dispatch_async(dispatch_get_main_queue()) { 
        print("Response: \(responseString!)") 
       } 
      } 

     } 
    } 

    task.resume() 

在處理互聯網連接故障方面，您應該檢查發送回來的回覆並決定要採取的行動。

if let httpResponse = response as? NSHTTPURLResponse { 
    println("error \(httpResponse.statusCode)") 
} 

Answer 2

發音!的正確方法是「我發誓我的節目的生活。」因爲這就是你在做的事情。爲什麼你覺得你必須使用!？使用guard-let一切努力爲你：

let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { 
     data, response, error in 

     guard error == nil else { 
      print("Error: \(error)") 
      return 
     } 

     guard let data = data else { 
      fatalError("error was nil, but no data. This should never happen") 
     } 

     guard let responseString = NSString(data: data, encoding: NSUTF8StringEncoding) else { 
      print("Couldn't decode data") 
      return 
     } 

     dispatch_async(dispatch_get_main_queue()) { 
      self.testLabel.text = "\(responseString)" 
     } 
    }