vant list组件滚动保留滚动条位置，需结合keepAlive使用

1、保存位置的前提是用的keepAlive组件来做缓存，app.vue代码

<template>
  <div id="app">
    <keep-alive>
      <router-view v-if='$route.meta.keepAlive'/>
    </keep-alive>
    <router-view  v-if='!$route.meta.keepAlive'/>
  </div>
</template>

2、在路由文件router.js，给每个路由meta添加scrollTop和keepAlive

 {
      path: '/home',
      name: 'home',
      component: resolve => require(['@/views/home/index.vue'], resolve),
      meta: {
        title: '首页',
        index: 1,
        keepAlive: true,
        scrollTop: 0
      }
    },
    {
      path: '/classify',
      name: 'classify',
      component: resolve => require(['@/views/classify/index.vue'], resolve),
      meta: {
        title: '分类',
        index: 1,
        keepAlive: true,
        scrollTop: 0
      }
    },
    {
      path: '/shopping',
      name: 'shopping',
      component: resolve => require(['@/views/shopping/index.vue'], resolve),
      meta: {
        title: '购物车',
        index: 1,
        keepAlive: true,
        scrollTop: 0
      }
    },
    {
      path: '/detail',
      name: 'detail',
      component: resolve => require(['@/views/detail/index.vue'], resolve),
      meta: {
        title: '详情',
        index: 2,
        // keepAlive: true,
        // scrollTop: 0
      }
    },

3、然后在main.js,记录滚动条的位置

router.beforeEach((to, from, next) => {  
  if (from.meta.keepAlive) {
    const $wrapper = document.querySelector('.app-wrapper'); // 列表的外层容器 注意找到滚动的盒子
    const scrollTop = $wrapper ? $wrapper.scrollTop : 0;
    console.log('scrollTop=', scrollTop)
    from.meta.scrollTop = scrollTop;
  }
  next();
});

4、最后在需要记录保留滚动条位置的地方获取通过activated（这个函数每次进入页面都会执行，只有结合使用keepAlive组件才有效）来获取scrollTop，

  activated () {
    const scrollTop = this.$route.meta.scrollTop;
    const $wrapper = document.querySelector('.app-wrapper');
    if (scrollTop && $wrapper) {
      $wrapper.scrollTop = scrollTop;
    }
  },

比如缓存了某些页面也不想随之滚动，则把scrollTop置0即可；

activated() {
    const $wrapper = document.querySelector(".app-wrapper");
    $wrapper.scrollTop = 0;
  },

注意，页面滚动的话，其他页面有滚动条的也会随之滚动，可以对其他页面里面处理，或者判断是否从详情页到列表页来判断是否缓存位置，如果不是，则回到顶部，但是注意路由钩子函数this的使用；