swift - NSURLSession:在展开可选值时意外发现 nil

Question

我正在尝试从我自己的 API 取回数据。我可以在我的控制台日志中看到数据，但它一直给我 found nil 错误。

这是我的代码:

let request = NSMutableURLRequest(URL: NSURL(string: "linkHere")!)
    request.HTTPMethod = "POST"
    let postString = "sol=\(name)&sector=\(sector)"
    request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
    let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
        data, response, error in

        if error != nil {
            print("error=\(error)")
            return
        }

        print("response = \(response)")

        let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
        print("responseString = \(responseString)")
        do {
            self.json = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableLeaves) as? NSDictionary
        } catch let error as NSError{
         print("TEST Error \(error)")
        }

           if let parseJSON = self.json {


            dispatch_async(dispatch_get_main_queue())
                {

                    let storyboard = UIStoryboard(name: "Main", bundle: nil)

                    let vc = storyboard.instantiateViewControllerWithIdentifier("detailView") as! detailViewController
                     let x = parseJSON["sector"] as! String
                    vc.secLab = x
                    self.presentViewController(vc, animated: true, completion: nil)

            }
         }

    }
    task.resume()

在我的控制台日志中，我可以看到数据，请参见下图:

我做错了什么？

Answer 1

基本上，在捕获错误并仅打印错误后继续执行“良好”代码是一个坏主意。

如果您在 try 分支中展开转换类型，它会在成功时成为非可选类型，否则会捕获相应的错误。

语法应该是这样的

do {
  self.json = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableLeaves) as! [AnyObject]
  dispatch_async(dispatch_get_main_queue())
    {
      let storyboard = UIStoryboard(name: "Main", bundle: nil)

      let vc = storyboard.instantiateViewControllerWithIdentifier("detailView") as! detailViewController
      let dict = self.json[0] as! [String:AnyObject]
      let x = dict["sector"] as! String
      vc.secLab = x
      self.presentViewController(vc, animated: true, completion: nil)
  }
} catch let error as NSError{
  print("TEST Error \(error)")
}