JSON文本不是以数组或对象和选项开头，以允许未设置片段 - Swift 3.0

Question

我有一个问题。

如何读取JSON数据并将其显示为UILabel？错误说

“JSON文本没有以数组或对象开头，并且选项允许未设置片段”

我有这些PHP代码提取JSON数据如下：

{"login":"ID0001"}

test.php的

<?php
    $connect = mysqli_connect("","","","");
    global $connect;
    if(isset($_POST['login'])) {
        $login  = $_POST['login'];
        $sql    = "SELECT * FROM table WHERE login='$login'";
        $result = mysqli_query($connect, $sql);
        if($result && mysqli_num_rows($result) > 0) {
            while($row = mysqli_fetch_array($result)){
                $login_db = $row['login'];
                $output   = array ('login'=>$login_db);
            }
            print (json_encode($output));
        mysqli_free_result($result);
        }
        else {
            echo "No data found!";  
            echo mysqli_error($connect);
        }
    }
    else {
        echo "No input";
    }   
?>

但在x代码中，我无法打印JSON数据，无法在UILabel _loginLbl 上显示它。有人可以帮我解决这个问题吗？

ViewController.swift

import UIKit
class ViewController: UIViewController {
    @IBOutlet var _login: UITextField!
    @IBOutlet var _loginLbl: UILabel!
    @IBOutlet var sendButton: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func sendData(_ sender: Any) {
        let login = _login.text
        if(login == "") {
            print("No value entered")
            return
        }

        let postString = "login=\(login)"
        print("JSON value =\(postString)")

        let url = URL(string: "http://localhost/get.php")
        var request = URLRequest(url: url!)
        request.httpMethod = "POST"
        request.httpBody = postString.data(using: String.Encoding.utf8)
        let task = URLSession.shared.dataTask(with: request) { (data, response, error) in

            guard let data = data else {
                self._loginLbl.text = "Error data"
                print("Error result =\(error)")
                return
            }
            do {

                print("Value here")
                if let json = try JSONSerialization.jsonObject(with: data) as? [String: String] {
                    DispatchQueue.main.async {
                        let loginvalue = json["login"]
                        self._loginLbl.text = loginvalue;
                        print(json)
                    }
                }
            } 
            catch let parseError
            {
                print("Catch error: \(parseError)")
                self._loginLbl.text = "Catch error";

                let responseString = String(data: data, encoding: .utf8)
                print("response :\(responseString)")
            }
        }
        task.resume()
    }
}

感谢。