通过mPdf在codeigniter中获取生成的pdf的空白附件

Question

这是我的功能。我正在生成一个pdf并尝试邮寄它。我已经检查了我的电子邮件库，它工作正常，但生成的pdf为空白附件。

function voucherEmail()
{

    $this->load->library('m_pdf');

    ob_start();

    $day = date('d');
    $year = date('Y');
    $month = date('F');

    echo "Hello World Today is $month $day, $year";

    $html = ob_get_contents();

    ob_end_clean();

    $this->m_pdf->pdf->WriteHTML(($html));

    $content = $this->m_pdf->pdf->Output('','S');

    $filename = "giftVoucher.pdf";

    $config = array();
    $config['useragent']           = "CodeIgniter";
    $config['protocol']            = "sendmail";
    $config['smtp_host']           = "localhost";
    $config['smtp_port']           = "25";
    $config['mailtype']            = "html";
    $config['charset']             = "iso-8859-1";


    $this->load->library('email',$config);

    $this->email->set_newline("\r\n");
    $this->email->from('voucher@theholidaysclubs.com', 'The Holidays Club:Gift Voucher');
    $this->email->to('shikhachauhan862@gmail.com');
    $this->email->subject('The Holidays Club:Gift Voucher');
    $this->email->attach($content,'attachment',$filename,'application/pdf');
    $this->email->send(); 

}

有人可以请我出错吗