NSMutableURLConnection中的POST请求返回nil，而相同的GET请求工作正常

Question

我一直在研究iOS程序，而且我遇到了一些问题。我最近一直在测试一个使用GET方法登录的简单系统，但我需要使用POST来保证安全性，所以我切换了。错误发生在＆＃39; if let dictionary＆＃39;行，错误是它试图打开一个nil可选。虽然它具有完全相同的数据，但它仍然不起作用。想法？提前谢谢。

的iOS：

class ViewController: UIViewController {

    var json: NSMutableData = NSMutableData()
    var data: [[String: String]]!

    @IBOutlet weak var usernameTextField: UITextField!
    @IBOutlet weak var passwordTextField: UITextField!
    @IBOutlet weak var activityIndicator: UIActivityIndicatorView!

    @IBAction func attemptLogin(sender: UIButton) {
        if(usernameTextField.text == "" || passwordTextField.text == "") {
            var alert = UIAlertController(title: "Error", message: "Invalid Credentials", preferredStyle: UIAlertControllerStyle.Alert)
            alert.addAction(UIAlertAction(title: "Close", style: UIAlertActionStyle.Default, handler: nil))
            self.presentViewController(alert, animated: true, completion: nil)
        } else {
            attemptConnection(usernameTextField.text, password: passwordTextField.text)
        }
    }

    func parseJSON(inputData: NSData) -> [[String: String]]{
        var error: NSError?
        var dictionary: [[String: String]]!

        if (inputData.length != 0) {
            if let dictionary = NSJSONSerialization.JSONObjectWithData(inputData, options: NSJSONReadingOptions.MutableContainers, error: &error) as? [[String: String]] {

            } else {

            }
        }

        return dictionary
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        var tapBackground: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: "dismissKeyboard:")
        tapBackground.numberOfTapsRequired = 1;
        self.view.addGestureRecognizer(tapBackground)
    }

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

    func dismissKeyboard(sender: AnyObject) {
        self.view.endEditing(true)
    }

    func attemptConnection(username: String, password: String){
        let urlPath: String = "https://codekaufman.com/getusers.php"
        var url: NSURL = NSURL(string: urlPath)!
        var request: NSMutableURLRequest = NSMutableURLRequest(URL: url)

        request.HTTPMethod = "POST"

        let bodyData = ("username=" + usernameTextField.text + "&password=" + passwordTextField.text as NSString).dataUsingEncoding(NSUTF8StringEncoding)
        request.HTTPBody = bodyData

        var connection: NSURLConnection = NSURLConnection(request: request, delegate: self, startImmediately: false)!
        connection.start()
        activityIndicator.startAnimating()
        self.view.userInteractionEnabled = false
    }

    func connection(connection: NSURLConnection!, didReceiveData data: NSData!){
        self.json.appendData(data)
    }

    func connectionDidFinishLoading(connection: NSURLConnection!) {
        activityIndicator.stopAnimating()
        self.view.userInteractionEnabled = true
        data = parseJSON(json)

        println(data.count)

        if(data.count != 0) {
            self.performSegueWithIdentifier("login", sender: self)
            println(data[0])
            println(data[0]["first_name"]!)
        } else {
            self.view.backgroundColor = UIColor.redColor()
        }

    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if (segue.identifier == "login") {
            var svc = segue.destinationViewController as SecondViewController;
            svc.data = self.data
        }
    }

}

PHP：

try {
    $dbh = new PDO('mysql:host=localhost; dbname=codeggdj_users', $username, $password);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $recievedUsername = $_POST['username'];
    $recievedPassword = $_POST['password'];

    $sth = $dbh->prepare('SELECT password FROM users WHERE username = ?');
    $sth->execute([$recievedUsername]);

    if($sth->rowCount()) {
       $row = $sth->fetch(PDO::FETCH_OBJ);

       if(password_verify($recievedPassword, $row->password)) {
           $sth = $dbh->prepare('SELECT id, username, first_name, last_name FROM users WHERE username = ?');
           $sth->execute([$recievedUsername]);

           echo json_encode($row = $sth->fetchAll(PDO::FETCH_ASSOC));
       } else {
           echo 'Incorrect Password';
       }
    } else {
       echo 'Incorrect Username';
    }

} catch(PDOException $e) {
    echo $e->getMessage();
}