执行 segue swift 4

Question

我正在尝试使用我的数据库验证用户的登录。当按下登录按钮时，我想根据从数据库返回的信息来判断是否会发生转场。我从最初设置为 true 的变量决策开始，如果我无法验证用户，我想将其设置为 false 并防止 segue。这是我的代码，但它有问题。最后的 return 语句始终为真。基本上发生的事情是在从数据库返回响应之前首先调用 .resume() 之后最后的 return 语句。有人可以澄清为什么会发生这种情况

 override func shouldPerformSegue(withIdentifier identifier: String,sender: 
 Any?) -> Bool
 {
             var decision = true
            let url = URL(string:"http://192.23.25.98/login/php")
            var request = URLRequest(url: url!)
            request.httpMethod = "POST"
            let body = "UserNameLogIn=\(userName.text!.lowercased())&PasswordLogIn=\(passWord.text!.lowercased())"
            request.httpBody=body.data(using: String.Encoding.utf8)
            URLSession.shared.dataTask(with: request) { (data:Data?, response:URLResponse?, error:Error?) in
                if (error == nil)
               {
                    DispatchQueue.main.async(execute: {
                        do
                        {
                            let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? Dictionary<AnyHashable,AnyObject>
                            guard let parseJson = json else{
                                print ("error parsing")
                                return
                            }
                            let status = parseJson["status"]
                            if (status != nil)
                            {
                                if (parseJson.count>3)
                                {
                                    decision = true

                                }
                                else
                                {
                                    decision = false


                                }
                            }
                        }
                        catch
                        {

                            print("error: \(error)")
                        }
                    })
                }
                else
                {
                    decision = false
                }
                }.resume()
    return decision
}

Answer 1

与其在点击按钮时启动 segue 并尝试在 shouldPerformSegue(withIdentifier:sender:) 中捕获异步过程，不如让按钮定义一个 @IBAction 来执行验证请求并以编程方式启动 segue，如果它成功了。

因此：

1. 从按钮中移除 segue。

2. 通过control在视图控制器之间添加segue - 从第一个场景上方栏中的视图控制器图标拖动到第二个场景：

3. 选择 segue 并在属性检查器中为其命名：

4. 从按钮中移除 segue 后，您现在可以将按钮连接到 @IBAction 方法：

5. 当您完成验证逻辑时，您的登录操作应该performSegue(withIdentifier:sender:)：

   performSegue(withIdentifier: "NextSceneSegue", sender: self)
   

   例如

   @IBAction func didTapLoginButton(_ sender: Any) {
       let url = URL(string:"http://192.23.25.98/login/php")
       var request = URLRequest(url: url!)
       request.httpMethod = "POST"
       request.httpBody = ["UserNameLogIn": useridTextField.text!, "PasswordLogIn": passwordTextField.text!]
           .map { $0.key + "=" + $0.value.addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed)! }
           .joined(separator: "&")
           .data(using: .utf8)
   
       URLSession.shared.dataTask(with: request) { data, response, error in
           DispatchQueue.main.async {
               guard let data = data, let httpResponse = response as? HTTPURLResponse, (200 ..< 300) ~= httpResponse.statusCode, error == nil else {
                   // handle basic network errors here
                   return
               }
   
               guard let json = (try? JSONSerialization.jsonObject(with: data)) as? [String: Any] else {
                   // handle json parsing errors here
                   return
               }
   
               if json["status"] == nil  {
                   // handle missing status here
                   return
               }
   
               guard json.count > 3 else {
                   // handle incorrect count here
                   return
               }
   
               self.performSegue(withIdentifier: "NextSceneSegue", sender: self)
           }
       }.resume()
   }
   

6. 注意，我对请求正文中的值进行百分比编码。尤其是密码，可能包含保留字符。而且我没有弄错使用.urlQueryAllowed，而是使用了.urlQueryValueAllowed，其中我抽出了几个保留字符：

   extension CharacterSet {
   
       /// Returns the character set for characters allowed in the individual parameters within a query URL component.
       ///
       /// The query component of a URL is the component immediately following a question mark (?).
       /// For example, in the URL `http://www.example.com/index.php?key1=value1#jumpLink`, the query
       /// component is `key1=value1`. The individual parameters of that query would be the key `key1`
       /// and its associated value `value1`.
       ///
       /// According to RFC 3986, the set of unreserved characters includes
       ///
       /// `ALPHA / DIGIT / "-" / "." / "_" / "~"`
       ///
       /// In section 3.4 of the RFC, it further recommends adding `/` and `?` to the list of unescaped characters
       /// for the sake of compatibility with some erroneous implementations, so this routine also allows those
       /// to pass unescaped.
   
       static var urlQueryValueAllowed: CharacterSet = {
           let generalDelimitersToEncode = ":#[]@"    // does not include "?" or "/" due to RFC 3986 - Section 3.4
           let subDelimitersToEncode = "!$&'()*+,;="
   
           var allowed = CharacterSet.urlQueryAllowed
           allowed.remove(charactersIn: generalDelimitersToEncode + subDelimitersToEncode)
           return allowed
       }()
   
   }