在NSURLConnection中建立错误案例，在Swift中进行JSON解析

Question

我试图从我的网站上的JSON中提取信息。这样做时，如果连接出现错误，它应该返回该错误并将其记录到控制台。我遇到的问题是，如果我打开飞机更多或以其他方式丢失信号，错误：fatal error: unexpectedly found nil while unwrapping an Optional value崩溃应用程序。为什么它返回这个，当我设置了错误的条件来简单地记录？先谢谢你！

我不确定为什么错误没有被记录并且防止应用程序崩溃。任何指针都会有帮助。

JSONLoader.swift

import Foundation 

var arrayOfMeals: [Meal] = [Meal]() 
var weekDayArray = ["monday"] 


func getJSON(urlToRequest: String) -> NSDictionary { 

    var url: NSURL = NSURL(string: urlToRequest)! 
    var jsonRequest: NSURLRequest = NSURLRequest(URL: url) 
    var jsonResponse: AutoreleasingUnsafeMutablePointer<NSURLResponse?> = nil 

    var error: NSError? 
    var dataValue: NSData = NSURLConnection.sendSynchronousRequest(jsonRequest, returningResponse: jsonResponse, error:&error)! 

    if error? == nil { 
     var jsonResult: NSDictionary = NSJSONSerialization.JSONObjectWithData(dataValue, options: NSJSONReadingOptions.MutableContainers , error: &error) as NSDictionary 
     NSURLRequestCachePolicy.ReloadIgnoringLocalAndRemoteCacheData 
     if error? == nil { 
      return jsonResult 
     } 
     else { 
      return NSDictionary(object: "Error: Something with parsing went wrong :(", forKey: "error") 
     } 
    } 
    else { 
     return NSDictionary(object: "Error: There was an error with your connection :(", forKey: "error") 
    } 

} 

func loadJSON(jsonDictionary: NSDictionary) { 

    for days in weekDayArray{ 
     var resultsArray = jsonDictionary[days] as NSArray 
     for obj: AnyObject in resultsArray{ 
      let breakfast = (obj.objectForKey("breakfast")! as String) 
      let lunch = (obj.objectForKey("lunch")! as String) 
      let dinner = obj.objectForKey("dinner")! as String 
      let dateString = obj.objectForKey("dateString")! as String 
      let dayOfWeek = obj.objectForKey("dayOfWeek")! as String 
      let newMeal = Meal(breakfast: breakfast, lunch: lunch, dinner: dinner, dayOfWeek: dayOfWeek, dateString: dateString) 
      if theDays(newMeal.dateString) >= 0 { 
       arrayOfMeals.append(newMeal) 
      } 
     } 
    } 


} 

我期望功能的getJSON建立一个NSURLConnection的现场，解析JSON日期，并返回一个NSDictionary。如果连接中有错误，则会建立一个错误情况，然后它返回字典并提供解释错误的值。解析JSON文件时会出现额外的错误情况，并返回一个类似错误的NSDictionary。

我期望loadJSON函数能够创建对象Meal的实例，我们将其定义为具有早餐，午餐，晚餐，日期和星期几的属性。此实例的值是从函数getJSON返回的NSDictionary的结果。如果今天是未来，请将其附加到我的arrayOfMeals。否则，请忽略该实例。

MealViewController

override func viewDidLoad() { 
    super.viewDidLoad() 

    var req = getJSON("http://www.seandeaton.com/meals/Mealx") 
    loadJSON(req) 


} 

MealModel.swift - 创造饭菜的实例

class Meal { 

    let breakfast: String 
    let lunch: String 
    let dinner: String 
    let dayOfWeek: String 
    let dateString: String 

    init(breakfast: String, lunch: String, dinner: String, dayOfWeek: String, dateString: String) { 

     self.breakfast = breakfast 
     self.lunch = lunch 
     self.dinner = dinner 
     self.dayOfWeek = dayOfWeek 
     self.dateString = dateString 

    } 

} 

我怎样才能阻止应用失败后轰然建立连接并记录错误消息的安慰？再次感谢。

Answer 1

关键的发现是，在调用sendSynchronousRequest你检索NSData中，您已经定义NSData不是可选的，你附加了!这将迫使可选的返回值的解缠。因此，如果可选的NSData是nil（如果有任何网络问题会发生这种情况），则此代码将失败。

取而代之，您应该简单地将NSData作为可选项（即NSData?）并在尝试展开它之前检查它是否为nil。因此，我可能会建议是这样的：

func retrieveJSON(urlToRequest: String) -> NSDictionary { 

    let url: NSURL = NSURL(string: urlToRequest)! 
    let jsonRequest: NSURLRequest = NSURLRequest(URL: url) 

    var jsonResponse: NSURLResponse? 
    var error: NSError? 
    let dataValue = NSURLConnection.sendSynchronousRequest(jsonRequest, returningResponse: &jsonResponse, error:&error) 

    if dataValue != nil { 
     if let jsonResult = NSJSONSerialization.JSONObjectWithData(dataValue!, options: .MutableContainers, error: &error) as? NSDictionary { 
      return jsonResult 
     } else { 
      return [ 
       "error": "Error: Something with parsing went wrong :(", 
       "localizedDescription": error?.localizedDescription ?? "" 
      ]; 
     } 
    } 
    else { 
     return [ 
      "error": "Error: There was an error with your connection :(", 
      "localizedDescription": error?.localizedDescription ?? "" 
     ]; 
    } 
} 

以上将修复崩溃从可选NSData被迫去包裹，这本来是nil如果有网络问题导致。请注意，您不会向我们显示调用getJSON并随后调用loadJSON的代码，但我假设您正在执行必要的错误处理检查。

请注意，我也退休了尴尬AutoreleasingUnsafeMutablePointer<NSURLResponse?>构造。我还将错误的localizedDescription添加到正在返回的字典中。

就个人而言，我通常会返回完整的NSError对象和NSURLResponse对象，以便调用者可以诊断错误的确切性质，而不仅仅是文本描述。

---

在一个更激进的修改您的代码，我建议你尽量避免使用同步请求。切勿从主线程执行同步请求。

例如，您可以定义的方法来异步执行请求，就像这样：

func retrieveJSON(urlToRequest: String, completionHandler:(responseObject: NSDictionary?, error: NSError?) ->()) { 

    let url: NSURL = NSURL(string: urlToRequest)! 
    let jsonRequest: NSURLRequest = NSURLRequest(URL: url) 

    var jsonResponse: NSURLResponse? 
    NSURLConnection.sendAsynchronousRequest(jsonRequest, queue: NSOperationQueue.mainQueue()) { 
     response, data, error in 

     if data == nil { 
      completionHandler(responseObject: nil, error: error) 
     } else { 
      var parseError: NSError? 
      let jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: &parseError) as NSDictionary? 
      completionHandler(responseObject: jsonResult, error: error) 
     } 
    } 
} 

你会再调用它，使用“后关闭语法”，像这样：

retrieveJSON(urlString) { 
    responseObject, error in 

    if responseObject == nil { 
     // handle error here, e.g. 

     println(error) 
     return 
    } 

    // handle successful the `NSDictionary` object, `responseObject`, here 
} 

// but don't try to use the object here, because the above runs asynchronously