vue.js 实现点击展开收起动画效果

<template>
  <div class="dealRecord-wrap">
    <div class="title-contant" v-for="(item,index) in items " >

      <div class="title" @click="showHide(index)">

        <h3>2018年0{{index+6}}月</h3>

        <div class="number">800笔<i></i></div>

      </div>

      <div class="contant">

        <ul>

          <li v-for="i in item.allNumber">
            {{index+6}}
          </li>
        </ul>
      </div>
    </div>
  </div>
</template>
<script>
export default{
  data(){
    return{
      items:[
        {v:'qqq',allNumber:1},

        {v:'aaa',allNumber:2},

        {v:'qqq',allNumber:3},

      ],
    }
  },
  created(){
    document.body.style.backgroundColor = '#f6f6f6';
  },

  mounted(){

    for(var i=0;i<3;i++){  //这里取值自后台返回的长度,设置页面渲染完成后是否展开，此处不展开

      document.getElementsByClassName('contant')[i].style.height = '0px';

    }

  },

  ponents:{

  },

  methods:{

    showHide(index){  //点击展开收起

      let contant = document.getElementsByClassName('contant')[index];  //这里我们通过参数index来让浏览器判断你点击的是哪一个列表  

      let height = contant.getBoundingClientRect().height;  //获取页面元素的当前高度

      document.getElementsByTagName('i')[index].style.transform = !!height?'rotateX(0deg)':'rotateX(180deg)';

      if (!!height) {

      contant.style.height = height + 'px';

      let f = document.body.offsetHeight; //强制相应dom重绘，使最新的样式得到应用

      contant.style.height = '0px';

      } else {

      contant.style.height = 'auto';

      height = contant.getBoundingClientRect().height;

      contant.style.height = '0';

      let f = document.body.offsetHeight;

      contant.style.height = height + 'px';

      }
    }
  },

  beforeDestroy(){
    document.body.style.backgroundColor = '#fff';
  }
}
</script>
<style type="text/scss" lang="scss" scoped>
.dealRecord-wrap{margin-bottom: 100px;

  .title-contant{overflow: hidden;  / 这个是重点 /

    .title{height: 84px;padding: 0 24px;border-bottom: 1px solid #eaeaea;/px/

      h3{height: 84px;font-size: 28px;color: #333;display: flex;align-items: center;float: left;;margin-left: 10px;}

      .number{height: 84px;font-size: 24px;color: #666;display: flex;align-items: center;float: right;}

      .number i{display: inline-block;width: 23px;height: 13px;background: url('../../assets/images/icon_dropup@2x.png');background-repeat: no-repeat;background-size: 23px 13px;background-position: right 6px center;padding-right: 35px;display: flex;align-items: center; float: right;transform:rotateX(0deg);}

    }

    .contant{background: #fff;transition: height 1s;  / 这个也是重点 /

      ul li{padding: 0 24px;height: 142px;display: flex;align-items: center;}

      ul li:not(:last-child){border-bottom: 1px solid #f6f6f6;/px