init_openid

	/**
	 * 获取用户openid
	 */
	private function init_openid() {
		//$_SESSION["openid"] = "oXLtZwWQjTxJUF_qiXbsjS30Usyc";
        if(empty($_SESSION['openid'])) {
			include_once(APPPATH . 'library/Wxpay.php');
            $jsApi = new JsApi_pub();
            if (! isset($_GET['code'])) {
                //触发微信返回code码
                $url = $jsApi->createOauthUrlForCode();
                Header("Location: $url");
            } else {
                //获取code码，以获取openid
				$_SESSION["openid"] = $openid = $jsApi->getOpenId($_GET['code']);
				if (! $openid) {
					$this->error("获取异常，请联系管理员！");
				}
            }
        } else {
			 $openid = $_SESSION['openid'];
		}
        return $openid;
	}