MySQL-致命错误：调用成员函数

Question

试图创建一个登录屏幕，我得到一个错误

致命错误：在第19行的C：\xampp\htdocs\login\class\Mysql.php中，对非对象调用成员函数准备（）

    <?php 

require_once 'includes/constants.php';

class Mysql {
    private $conn;

    function __construct() {
        $this->conn = new mysqli (DB_SERVER, DB_USER, DB_PASSWORD, DB_NAME) or die('There was a problem connecting to the database.');  
    }

    function verify_Username_and_Pass($un, $pwd) {

        $query = "SELECT *
                    FROM users
                    WHERE username = ? AND password = ?
                    LIMIT 1";

        if($stmt = $this->conn->prepare($query)) {
            $stmt->bind_param('ss', $un, $pwd);
            $stmt->execute();

            if($stmt->fetch()) {
                $stmt->close();
                return true;
            }
        }
    }
}

Constants.php

<?php
// Define constants here

define('DB_SERVER', '192.168.2.50:3306');
define('DB_USER', 'user');
define('DB_PASSWORD', 'pass');
define('DB_NAME', 'membership');

Answer 1

确保"user"具有对数据库成员资格的授予

grant all on membership.* to user@localhost identified by 'pass'