需求描述：

如下图，可收缩、可展开的侧边导航栏，当收缩时，鼠标悬停在一级菜单时，出现二级菜单。

解决方法：

设置标志【isCollapse】来控制展开和收缩图标的显示，当【isCollapse=true】时，侧标导航栏收缩，且标题“通讯录管理”不显示。当【isCollapse=false】时，侧标导航栏展开，且标题“通讯录管理”显示。

在展开和收缩图标上绑定点击事件【@click="isCollapse=true"】【@click="isCollapse=false"】

 <span>
        <!-- <i class="el-icon-platform-eleme logo"></i> -->
        <img src="../../assets/images/通讯录.png" alt />
        <span v-show="!isCollapse">通讯录管理</span>
      </span>
      <el-radio-group v-model="isCollapse" style="margin-bottom: 20px;">
        <i v-show="!isCollapse" class="el-icon-s-fold expandBtn" @click="isCollapse=true"></i>
        <i v-show="isCollapse" class="el-icon-s-fold shrinkBtn" @click="isCollapse=false"></i>
      </el-radio-group>

注意，收缩图标采用固定定位

.shrinkBtn {
        position: fixed;
        left: -18px;
        top: 38px;
        color: #151d41;
        margin-left: 100px;
        transform: rotate(180deg);
      }

完整代码：

<template>
  <div class="left-nav">
    <!-- <button @click="isCollapse=!isCollapse">展开</button> -->
    <div class="nav-logo">
      <span>
        <!-- <i class="el-icon-platform-eleme logo"></i> -->
        <img src="../../assets/images/通讯录.png" alt />
        <span v-show="!isCollapse">通讯录管理</span>
      </span>
      <el-radio-group v-model="isCollapse" style="margin-bottom: 20px;">
        <i v-show="!isCollapse" class="el-icon-s-fold expandBtn" @click="isCollapse=true"></i>
        <i v-show="isCollapse" class="el-icon-s-fold shrinkBtn" @click="isCollapse=false"></i>
      </el-radio-group>
    </div>
    <el-menu
      class="el-menu-vertical-demo"
      :unique-opened="true"
      router
      background-color="#151d41"
      text-color="#fff"
      :collapse="isCollapse"
    >
      <el-menu-item index="/">
        <i class="el-icon-s-home"></i>
        <span slot="title">首页</span>
      </el-menu-item>
      <el-submenu v-for="(item,index) in menuList" :index="'' + index" :key="index">
        <template slot="title">
          <i :class="item.icon"></i>
          <span>{{ item.authName }}</span>
        </template>
        <el-menu-item
          v-for="(subItem,index) in item.children"
          :index="'/' + subItem.path"
          :key="index"
        >
          <span>{{ subItem.authName }}</span>
        </el-menu-item>
      </el-submenu>
    </el-menu>
  </div>
</template>

<script>
export default {
  data() {
    return {
      menuList: [
        {
          id: 0,
          authName: "通讯录",
          icon: "el-icon-s-custom",
          children: [
            {
              authName: "用户与部门管理",
              id: 1,
              path: "department",
              parentid: 0
            },
            { authName: "通讯录设置", id: 2, path: "adrbook", parentid: 0 }
          ]
        },
        {
          id: 1,
          authName: "数据报表",
          icon: "el-icon-s-claim",
          children: [
            { authName: "数据概览", id: 1, path: "overview", parentid: 1 },
            { authName: "员工活跃数据", id: 2, path: "employees", parentid: 1 }
          ]
        },
        {
          id: 2,
          authName: "企业设置",
          icon: "el-icon-office-building",
          children: [
            {
              authName: "企业信息管理",
              id: 1,
              path: "information",
              parentid: 2
            },
            { authName: "权限管理", id: 2, path: "authority", parentid: 2 },
            { authName: "团队邀请设置", id: 3, path: "team", parentid: 2 },
            { authName: "安全策略", id: 4, path: "safety", parentid: 2 },
            { authName: "管理员日志", id: 5, path: "journal", parentid: 2 }
          ]
        }
      ],
      isCollapse: false
    };
  },
  methods: {}
};
</script>

<style lang="less" scoped>
@bgc: #151d41;
.left-nav {
  // width: 228px;
  .nav-logo {
    height: 60px;
    padding: 0 10px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    line-height: 60px;
    margin-top: 16px;
    .logo {
      font-size: 30px;
    }
    img {
      width: 28px;
      margin: 5px;
    }
    .el-radio-group {
      font-size: 20px;
      line-height: 60px;
      margin-top: 20px;
      margin-left: 10px;
      .shrinkBtn {
        position: fixed;
        left: -18px;
        top: 38px;
        color: #151d41;
        margin-left: 100px;
        transform: rotate(180deg);
      }
    }
  }
  .el-menu-vertical-demo:not(.el-menu--collapse) {
    width: 200px;
    min-height: 400px;
  }

  .el-menu-vertical-demo {
    border: none;
    .el-menu-item {
      span {
        color: #909399;
        font-size: 16px;
      }
    }
    .el-submenu {
      span {
        color: #909399;
        font-size: 16px;
      }
      .el-menu-item {
        span {
          color: #909399;
          font-size: 14px;
        }
      }
    }
  }
}
</style>