修改文件：

1. flow.dwt 模板， 

2. flow.php 

首先

第一步 ：

修改购物车模板：

添加 数量减少/增加 按钮（这里用的span），input文本框按照下边参数设置好。

<div class="zz fl">
    <span onclick="red_num({$goods.rec_id},{$goods.goods_id});">-</span>
    <input type="text" name="goods_number[{$goods.rec_id}]" class="input2" value="{$goods.goods_number}" id="goods_number_{$goods.rec_id}"  onchange="change_price({$goods.rec_id},{$goods.goods_id})" />
    <span onclick="add_num({$goods.rec_id},{$goods.goods_id})">+</span>
</div>

第二步：

模板文件添加JS

<script type="text/javascript">
                        function add_num(rec_id,goods_id)
                        {
                            document.getElementById("goods_number_"+rec_id+"").value++;
                            var number = document.getElementById("goods_number_"+rec_id+"").value++;
                            
                            Ajax.call('flow.php', 'step=update_group_cart&rec_id=' + rec_id+'&number=' + number+'&goods_id=' + goods_id, changePriceRespone, 'GET', 'JSON');
                        }
                        function red_num(rec_id,goods_id)
                        {
                            if (document.getElementById("goods_number_"+rec_id+"").value>1)
                            {
                                document.getElementById("goods_number_"+rec_id+"").value--;
                            }
                            var number = document.getElementById("goods_number_"+rec_id+"").value;
                            Ajax.call('flow.php', 'step=update_group_cart&rec_id=' + rec_id+'&number=' + number+'&goods_id=' + goods_id, changePriceRespone, 'GET', 'JSON');
                        }
                        function change_price(rec_id,goods_id)
                        {
                            var number = document.getElementById("goods_number_"+rec_id+"").value;
                            Ajax.call('flow.php','step=update_group_cart&rec_id=' + rec_id+'&number=' + number+'&goods_id=' + goods_id, changePriceRespone, 'GET', 'JSON');
                        }
                        function changePriceRespone(result)
                        {
                            if(result.error == 1)
                            {
                                alert(result.content);
                                document.getElementById("goods_number_"+result.rec_id+"").value = result.number;
                            }else{
                                
                                document.getElementById('subtotal_'+result.rec_id).innerHTML = result.subtotal;//商品总价
                                document.getElementById('cart_amount_desc').innerHTML = result.cart_amount_desc;//购物车商品总价说明
                                document.getElementById('market_amount_desc').innerHTML = result.market_amount_desc;//购物车商品总市价说明
                            }
                        }
                        </script>

顺便模板文件数量、价格计算添加ID

<span id="subtotal_{$goods.rec_id}">{$goods.subtotal}</span>

<span id="cart_amount_desc">{$shopping_money}</span>

<span id="market_amount_desc">{$market_price_desc}</span>

第三步：

修改php文件

搜索：$_REQUEST['step'] == 'consignee' 在上方添加

elseif($_REQUEST['step']=='update_group_cart')
{
    //2016-05-24 cart_update
    include_once('includes/cls_json.php');
    $result = array('error' => 0, 'message' => '', 'content' => '', 'goods_id' => '');
    $json = new JSON;
    $rec_id = $_GET['rec_id'];
    $number = $_GET['number'];
    $goods_id = $_GET['goods_id'];
    $result['rec_id'] = $rec_id;
    if ($GLOBALS['_CFG']['use_storage'] == 1)
    {
        $goods_number = $GLOBALS['db']->getOne("select goods_number from ".$GLOBALS['ecs']->table('goods')." where goods_id='$goods_id'");
        if($number>$goods_number)
        {
            $result['error'] = '1';
            $result['content'] ='对不起,您选择的数量超出库存您最多可购买'.$goods_number."件";
            $result['number']=$goods_number;
            die($json->encode($result));
        }
    }
    $sql = "UPDATE " . $GLOBALS['ecs']->table('cart') . " SET goods_number = '$number' WHERE rec_id = $rec_id";
    $GLOBALS['db']->query($sql);
    /* 取得商品列表，计算合计 */
    $cart_goods = get_cart_goods();
    $subtotal = $GLOBALS['db']->getONE("select goods_price * goods_number AS subtotal from ".$GLOBALS['ecs']->table('cart')." where rec_id = $rec_id");
    $result['subtotal'] = price_format($subtotal, false);
    $result['cart_amount_desc'] = sprintf($_LANG['shopping_money'],$cart_goods['total']['goods_price']);
    $result['market_amount_desc'] = sprintf($_LANG['than_market_price'],$cart_goods['total']['market_price'],$cart_goods['total']['saving'],$cart_goods['total']['save_rate']);
    
    die($json->encode($result));
}

到这里完成Ajax异步数量增减！！！