mysqli 连接文件 Doesnt recoqnize prepare stement [duplicate]

问：

我的 php mysqli 文件出现错误。

致命错误：未捕获的错误：调用成员函数 prepare（） on null 输入 C：\Users\driek\Desktop\xampp\htdocs\driekvandermeulen.nl_3.0\php\main\contact1.php：20 堆栈跟踪：#0 C：\Users\driek\Desktop\xampp\htdocs\driekvandermeulen.nl_3.0\php\main\contact1.php（33）： writeDatabase（'dsgd'， '[email protected]'， 'gf'， 'awesrdtfgh'） #1 {main} 扔进去 C：\Users\driek\Desktop\xampp\htdocs\driekvandermeulen.nl_3.0\php\main\contact1.php 第 20 行

它没有重新定义第 20 行的准备语句，但我看不出它有什么问题。

    function dbConnect(){
        $servername = "localhost";                                          // Localhost stays untouched
        $username = "dbUser";                                               // Username of the MySQL database user
        $password = "R4b3Eg5Jt4Y9GKqB";                                         // Password of the MySQL database user
        $conn = new mysqli($servername, $username, $password);                  // Create connection
        if ($conn->connect_error) {                                                 // Check connection
            die("Connection failed: " . $conn->connect_error);
        }
        echo "Connected successfully";
        return;
    }

    function writeDatabase($p_sName,$p_sEmailAddress,$p_sSubject,$p_sMailContent){
       $conn = dbConnect();

    // -------------------- prepare and bind --------------------------------
        //$stmt = $conn->prepare("INSERT INTO `driekvandermeulen.tbl_emailcontacts` (`firstname`, `lastname`, `email`) VALUES (?, ?, ?, ?)");
        $stmt = $conn->prepare();
        $stmt->bind_param($p_sName,$p_sEmailAddress,$p_sSubject,$p_sMailContent);

                $stmt->execute(); // Actual save into the database
    }