如何在CodeIgniter中跨页面使用户对象可用？

$autoload['libraries'] = array('session');

public function login() {
    // 验证用户名和密码
    // ...

    // 如果验证成功，将用户数据存储到Session中
    $user_data = array(
        'user_id' => $user_id,
        'username' => $username,
        'logged_in' => TRUE
    );
    $this->session->set_userdata($user_data);
}

$user_id = $this->session->userdata('user_id');
$username = $this->session->userdata('username');

$autoload['libraries'] = array('cookie');

public function login() {
    // 验证用户名和密码
    // ...

    // 如果验证成功，将用户数据存储到Cookie中
    $user_data = array(
        'user_id' => $user_id,
        'username' => $username
    );
    $this->input->set_cookie('user_data', json_encode($user_data), 86400); // 有效期为1天
}

$user_data = json_decode($this->input->cookie('user_data', TRUE), TRUE);
$user_id = $user_data['user_id'];
$username = $user_data['username'];