调用未定义的方法Database :: prepare（）oop pdo

Question

我的用户类中有一个构造函数：

            public function __construct($pdo)
            {
                $this->pdo = $pdo;
            }

这就是我经常运行的方式：

的index.php：

include("config.php");
$users = new Users($pdo);

但我不想这样做，我想为数据库连接分开一个类

创建了database.class.php

class Database
{
    public function __construct()
    {
        try
        {
            $pdo = new PDO('mysql:host='.MYSQL_HOST.';dbname=driptone', MYSQL_USER, MYSQL_PASSWORD);
            $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            echo 'connected';
        }
        catch(PDOException $e)
        {
            echo $e->getMessage();
        }
    }
}

现在我像这样使用它：

$users = new Users(new Database());

我收到此错误：

connected
Fatal error: Call to undefined method Database::prepare() in C:\xampp\htdocs\drip\class\users.class.php on line 75

我也尝试过一个静态的问题。

为什么会这样？我该如何解决？它是否能够安全地进行注射/ XSS攻击？

            /**
            * Public Method Register
            *
            * Registers the user to the system, checking for errors.
            * If error was found, it will throw new exception.
            *
            * @parm username The username the user posted.
            * @parm password The password the user posted.
            * @parm repassword The validated password the user posted.
            * @parm email The email the user posted.
            * @parm reemail The validated email the user posted.
            * @parm day The day the user posted (for date of birth).
            * @parm month The month the user posted (for date of birth).
            * @parm year The year the user posted (for date of birth).
            *
            * @return Return true means everything is correct, register successfully.
            **/

            public function register($username, $password, $repassword, $email, $reemail, $day, $month, $year)
            {
                    global $pdo;

                    // Check if passwords matching.
                    if ($password != $repassword)
                    {
                            throw new exception ("Passwords does not match.");
                    }
                    // Check if emails matching.
                    else if ($email != $reemail)
                    {
                            throw new exception ("Emails does not match.");
                    }

                    // The main insert query
                    $this->insert = $this->pdo->prepare
                    ("
                            INSERT INTO users
                            (user_name, user_password, user_email, user_birth)
                            VALUES
                            (:username, :password, :email, :birth)
                    ");

                    //Query to check if username is taken.
                    $this->user = $this->pdo->prepare("SELECT * FROM users WHERE user_name = :name");
                    $this->user->execute(array(":name" => $username));

                    //Query to check if email is taken.
                    $this->email = $this->pdo->prepare("SELECT * FROM users WHERE user_email = :email");
                    $this->email->execute(array(":email" => $email));                      

                    // Checking if username is taken using the query.
                    if ($this->user->rowCount())
                    {
                            throw new exception ("Username already in use");
                    }
                    // Checking if email is taken using the query.                 
                    else if ($this->email->rowCount())
                    {
                            throw new exception ("Email is already in use");
                    }
                    // Checking if birth of date is valid.
                    else if ($day > 31 || $month > 12 || $year > date('Y') || $year < 1925)
                    {
                            throw new exception ("Invalid Birth of date");
                    }
                    // Checking if password is more than 5 characters long.
                    else if (strlen($password) < 5)
                    {
                            throw new exception ("Password is too short");
                    }
                    else
                    {
                            // Everything is fine, insert data.

                            $this->insert->execute(array
                            (
                                    ":username" => $username,
                                    ":password" => $password,
                                    ":email" => $email,
                                    ":birth" => $day.'/'.$month.'/'.$year
                            ));

                            //Send verification

                            $this->sendVerification($username, $email);
                            //Finished processing, return true.
                            return true;
                    }
            }