致命错误，run_query是一个函数吗？

Question

  

致命错误：未捕获错误：在/home/matrixhub/public_html/login.php:64中调用null上的成员函数run_query（）   堆栈跟踪：
   第64行/home/matrixhub/public_html/login.php中引发＃0 {main}

我认为run_query是一个功能但是没问题。以下是第57至79行：

if (isset($_POST['login'])) {

    $name = $_POST['username'];
    $password = $_POST['password'];


    $query = "SELECT * FROM users WHERE username = '$email'";
    $result = $obj->run_query($query);
    if ($count = mysqli_num_rows($result) > 0) {
        $row = $result->fetch_object();
        if (password_verify($password, $row->password)) {
            $_SESSION['email'] = $email;
            $_SESSION['username'] = $name;
            echo "Logged in";
        } else {
            echo "Not logged in";
        }
    } else {
        echo "<script>alert('Your username or password is incorrect!')</script>";
    }
}