下载JSON数据在NSHTTPURLResponse失败

我想从一个URL获取JSON文件并使用Swift返回内容。但是，代码在以下代码中的行let httpResponse = response as! NSHTTPURLResponse处失败。我在这条线上得到一个异常，Xcode进入调试模式。下载JSON数据在NSHTTPURLResponse失败

class func downloadJSONFile()->AnyObject 
    { 
     let requestURL: NSURL = NSURL(string: "http://www.learnswiftonline.com/Samples/subway.json")! 
     let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL) 
     let session = NSURLSession.sharedSession() 
     var json:AnyObject = "" 
     let task = session.dataTaskWithRequest(urlRequest) { 
      (data, response, error) -> Void in 

      let httpResponse = response as! NSHTTPURLResponse 
      let statusCode = httpResponse.statusCode 

      if (statusCode == 200) { 

       do{ 
        json = try NSJSONSerialization.JSONObjectWithData(data!, options:.AllowFragments) 

       }catch { 
        print("Error with Json: \(error)") 

       } 

      } 

     } 

     task.resume() 

     return json 
    }

我该如何解决这个问题？

来源

2016-03-08 Jake

你不*从异步调用的返回*。示例：http://stackoverflow.com/a/35358750/2227743另外，您不应强制转换响应，它可能不在此处，因此请首先检查错误参数。 – Moritz

有几个问题：

如果在请求中的任何错误，response将nil，因而你的企图迫使投它会导致致命的错误。处理网络响应时不要使用强制解包/转换。

这里有一个更深层的问题，你试图从异步运行的方法返回数据。你应该改变你的方法不返回任何东西本身，而是提供一个完成处理程序，通过它可以异步地传回相关数据：

class func downloadJSONFile(completionHandler:(AnyObject?) ->()) { 
    let requestURL: NSURL = NSURL(string: "http://www.learnswiftonline.com/Samples/subway.json")! 
    let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL) 
    let session = NSURLSession.sharedSession() 
    let task = session.dataTaskWithRequest(urlRequest) { data, response, error in 

     // check for fundamental networking errors 

     guard error == nil && data != nil else { 
      print(error) 
      completionHandler(nil) 
      return 
     } 

     // check to see if status code found, and if so, that it's 200 

     guard let httpResponse = response as? NSHTTPURLResponse where httpResponse.statusCode == 200 else { 
      completionHandler(nil) 
      return 
     } 

     do { 
      let json = try NSJSONSerialization.JSONObjectWithData(data!, options:[]) 
      completionHandler(json) 
     } catch let parseError as NSError { 
      print("Error with Json: \(parseError)") 
      completionHandler(nil) 
     } 
    } 

    task.resume() 
}

，然后你怎么称呼它，使用完成处理程序（或使用尾随的闭包语法，像图所示）：

APIClass.downloadJSONFile() { json in 
    guard json != nil else { 
     print("there was some problem") 
     return 
    } 

    // now you can use `json` here 

    dispatch_async(dispatch_get_main_queue()) { 
     // and if you're doing any model or UI updates, dispatch that back to the main queue 
    } 
} 

// but do not use `json` here, as the above runs asynchronously

注意，如果你想提供错误信息返回给调用程序，你可以改变它也返回错误信息，例如：

enum DownloadError : ErrorType { 
    case NetworkError(NSError?) 
    case NotHTTPResponse 
    case InvalidHTTPResponse(Int) 
    case JSONError(NSError) 
} 

class func downloadJSONFile(completionHandler:(AnyObject?, ErrorType?) ->()) { 
    let requestURL: NSURL = NSURL(string: "http://www.learnswiftonline.com/Samples/subway.json")! 
    let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL) 
    let session = NSURLSession.sharedSession() 
    let task = session.dataTaskWithRequest(urlRequest) { data, response, error in 

     guard error == nil && data != nil else { 
      completionHandler(nil, DownloadError.NetworkError(error)) 
      return 
     } 

     guard let httpResponse = response as? NSHTTPURLResponse else { 
      completionHandler(nil, DownloadError.NotHTTPResponse) 
      return 
     } 

     guard httpResponse.statusCode == 200 else { 
      completionHandler(nil, DownloadError.InvalidHTTPResponse(httpResponse.statusCode)) 
      return 
     } 

     do { 
      let json = try NSJSONSerialization.JSONObjectWithData(data!, options:[]) 
      completionHandler(json, nil) 
     } catch let parseError as NSError { 
      completionHandler(nil, DownloadError.JSONError(parseError)) 
     } 
    } 

    task.resume() 
}

而且，很明显，通话将改变拿两个参数：

APIClass.downloadJSONFile() { json, error in 
    guard json != nil && error == nil else { 
     print("there was some problem \(error)") 
     return 
    } 

    // and then it would be like before ... 
}

当在iOS中使用9和NSURLSession以后，它不会允许明文请求（即“http”是不允许的，默认情况下只有“https”）。您可以强制应用通过将以下内容添加到您的info.plist来允许非https请求。见https://stackoverflow.com/a/31254874/1271826更多信息

<key>NSAppTransportSecurity</key> 
<dict> 
    <key>NSExceptionDomains</key> 
    <dict> 
     <key>learnswiftonline.com</key> 
     <dict> 
      <!--Include to allow subdomains--> 
      <key>NSIncludesSubdomains</key> 
      <true/> 
      <!--Include to allow HTTP requests--> 
      <key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key> 
      <true/> 
      <!--Include to specify minimum TLS version--> 
      <key>NSTemporaryExceptionMinimumTLSVersion</key> 
      <string>TLSv1.1</string> 
     </dict> 
    </dict> 
</dict>

来源

2016-03-08 22:37:52 Rob

下载JSON数据在NSHTTPURLResponse失败

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