在网页中的扫码支付是让js主动轮询服务器的，但是在iOS的APP中，无法使用js，所以需要在PHP中做回调处理

public function wxNotify(){
    $this->load->model('User_model');
    $order_no = $this->input->post('order_no');
    ini_set('date.timezone','Asia/Shanghai');
    error_reporting(E_ERROR);
    require_once (__DIR__.'/../WXSDK0308/lib/WxPay.Api.php');
    require_once (__DIR__.'/../WXSDK0308/example/log.php');
    sleep(3);
    while($this->query($order_no)=='NOTPAY'){
        sleep(1);
        $this->query($order_no);
    }
    if($this->query($order_no)=='SUCCESS'){
        $update['from'] = 'orders';
        $update['where'] = "order_no= '$order_no' " ;
        $update['set'] = array(
            'is_pay'     => 1,
            'pay_time'   => time(),
            'pay_type'   => 'wx',
        );
        if($this->User_model->updateByCondition($update)){
            $info['mess'] = 'ok';
            $info['flag'] = 1;
            exit(json_encode($info));
        }else{
            $info['mess'] = 'Fail';
            $info['flag'] = 0;
            exit(json_encode($info));
        } 
    }
}

public function query($order_no){
    if(isset($order_no) && $order_no != ""){
        $out_trade_no = $order_no;
        $input = new WxPayOrderQuery();
        $input->SetOut_trade_no($out_trade_no);
        $result=WxPayApi::orderQuery($input);
        return $result['trade_state'];
    }else{
        return 500;  // no order_no
    }
}