public function getData()
{
$this->validate('app_id', 'mch_id', 'bill_date');
$data = array('appid' => $this->getAppId(), 'mch_id' => $this->getMchId(), 'device_info' => $this->getDeviceInfo(), 'bill_date' => $this->getBillDate(), 'bill_type' => $this->getBillType(), 'nonce_str' => md5(uniqid()));
$data = array_filter($data);
$data['sign'] = Helper::sign($data, $this->getApiKey());
return $data;
}