wx:for data-arg不会更新

<view class="app-moduler {{v.isDown?'grey':''}}" wx:for="{{cart}}" wx:for-item='v' wx:for-index="key">

    <view class="items {{move==key? 'slider_del':''}}" bindtouchstart="touchstart" bindtouchmove="touchEvent" data-arg="{{key}}">

      <view class="chb"><checkbox checked="{{v.num > 0&&!v.isDown?'checked':''}}" class="check wx-checkbox-input-checked" bindtap="trigger" data-arg="{{key}}" disabled="{{v.isDown?'true':'false'}}"></checkbox></view>

      <view class="mod-item">

      <image src="{{v.img}}" class="mod-image" bindtap="check_book" data-arg="{{key}}" mode="aspectFit"></image>

      <view class="mod-title" style="width: {{cw}}px;">

        <view class="catalog">商品：{{v.name}}</view>

        <view class="catalog">规格：{{v.cate}}<span class='split'>;</span>{{v.attr}}</view>

        <view class="catalog">单位：{{v.pub}}</view>

        <view class="catalog">备注：{{v.detail}}</view>

        <view class='order_tab'>

          <image src="{{rmb}}" class="rmb"></image>

          <text class="price">{{v.pri}}</text>

          <view class="add" style="width:{{cw*0.6}}px;">

            <view class="btn" style="background-image: url('https://www.hzjyhkj.top/static/imgs/dec.png');" catchtap="dec_one" data-arg="{{key}}"></view>

            <input class="num_tab" value="{{v.num}}" type="number" bindinput="change_num" data-arg="{{key}}"/>

            <view class="btn" style="background-image: url('https://www.hzjyhkj.top/static/imgs/add2.png');" catchtap="add_one" data-arg="{{key}}"></view>

          </view>

        </view>

      </view>

    </view>

    </view>

    <!-- <view style="width:{{dw}}">删除</view> -->

  </view>

调试器里面会更新 但是手机端第二行的data-arg不会更新 导致经常报错