Json出错:ErrorDomain =NSCocoaErrorDomain Code=3840 "无值&qu

你好，我是Swift 3和iOS开发的新手，我需要下载这个php文件提供的JSONObject(一个数组):

<?php
if($_SERVER["REQUEST_METHOD"]=="POST"){
    include 'connectioncm.php';
    showMessage();
}
function showMessage()
{
    global $connect;
    $query = "SELECT * FROM `message` ORDER BY `message`.`id` DESC; ";
    $result = mysqli_query($connect, $query);
    $number_of_rows = mysqli_num_rows($result);
    $temp_array = array();
    if($number_of_rows > 0){
        while ($row = mysqli_fetch_assoc($result)){
            $temp_array[] = $row;
        }
    }
    header('Content-Type: application/json');
    echo json_encode(array("message"=>$temp_array));
    mysqli_close($connect);
}

这是viewDidLoad函数

override func viewDidLoad() {
 super.viewDidLoad()
    let requestURL: NSURL = NSURL(string: "http://cm.890m.com/newsfeedshow.php")!
    let urlRequest: NSMutableURLRequest = NSMutableURLRequest(url: requestURL as URL)
    let session = URLSession.shared
    let task = session.dataTask(with: urlRequest as URLRequest) {
        (data, response, error) -> Void in
        let httpResponse = response as! HTTPURLResponse
        let statusCode = httpResponse.statusCode
        if (statusCode == 200) {
            print("Everyone is fine, file downloaded successfully.")
        }
        do{
            let json = try JSONSerialization.jsonObject(with: data!, options:.allowFragments)
            if let message = (json as?NSDictionary)?["message"] as? [[String: AnyObject]] {
                for station in message {
                    if let deleg = (station["messagedeleg"] as? String) {
                        if let name = (station["nomdeleg"] as? String) {
                            self.names.append(name)
                            self.post.append(deleg)

                        }
                    }
                }
            }
        }catch {
            print("Error with Json: '(error)")
        }
    }
    task.resume()
}

谁产生了这个错误:

Error with Json: ErrorDomain =NSCocoaErrorDomain Code=3840 "No value."用户信息= {NSDebugDescription = No值。}

宜兰Rossler .