##前言之前博客里分享过一篇用《Angular 实现树形菜单（多级菜单）功能模块》，而在由于战略转移，所以我给 Vue 也来了一份。功能差不多，不过由于这个是第二次做，会对之前的一些不足作一个修正。下面来看看 Vue 树形菜单。

在做这个 DEMO 的时候我是用了vue 的脚手架（vue-cli）的，关于脚手架可以看这里《Vue 脚手架（vue-cli）安装及详解》，上面的两篇文章到时也会发到掘金上，如果有需要的朋友可以收藏本文，以备不时之需。所以结构看起来就像下面这样（结构示意图）：

├── index.html
├── main.js
├── router
│ └── index.js # 路由配置文件
├── components # 组件目录
│ ├── App.vue # 根组件
│ ├── Home.vue # 大的框架结构组件
│ ├── TreeView.vue
│ ├── TreeViewItem.vue
│ └── TreeDetail.vue
├── store
├── index.js # 我们组装模块并导出 store 的地方
├── modules # 模块目录
└── menusModule.js # 菜单模块

这个多级菜单实现的功能如下：

1、可展示多级菜单，理论上可以展无限级菜单
2、当前菜单高亮功能
3、刷新后依然会自动定位到上一次点击的菜单，即使这个是子菜单，并且父菜单会自动展开
4、子菜单的显示隐藏有收起、展开，同时带有淡入效果

这个例子用到的知识点：路由、状态管理、组件。

状态管理安装：

npm install --save vuex

更多关于 vuex 的介绍可以看官方文档：https://vuex.vuejs.org/zh-cn/。

我们先来看看效果演示图：

程序员是用代码来沟通的，所以费话不多说，直接上码：

index.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <title>Vue 实现树形菜单（多级菜单）功能模块- 云库网</title>
  </head>
  <body>
    <div id="app"></div>
  </body>
</html>

main.js

import Vue from 'vue'
import App from './components/App'
import router from './router'
import store from './store/index'
Vue.config.productionTip = false
/* eslint-disable no-new */
new Vue({
  el: '#app',
  router,
  store,
  components: {
    App
  },
  template: '<App/>'
})

在 main.js 中引入路由和状态管理配置

App.vue

<template>
  <div id="app">
    <Home></Home>
  </div>
</template>
<script>
import Home from "./Home";
export default {
  components: {
    Home
  },
  name: "App"
};
</script>
<style>
* {
  padding: 0;
  margin: 0;
}
#app {
  font-family: "Avenir", Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  color: #2c3e50;
}
html,
body,
#app,
.home {
  height: 100%;
}
html,
body {
 overflow: hidden;
}
</style>

Home.vue

<template>
  <div class="home">
       <div class="side-bar">
            <Tree-view></Tree-view>
       </div>
        <div class="continer">
            <router-view></router-view>
        </div>
  </div>
</template>
<script>
import TreeView from "./TreeView";
export default {
  components: {
    TreeView
  },
  name: "Home"
};
</script>
<style scoped>
.side-bar {
  width: 300px;
  height: 100%;
  overflow-y: auto;
  overflow-x: hidden;
  font-size: 14px;
  position: absolute;
  top: 0;
  left: 0;
}
.continer {
  padding-left: 320px;
}
</style>

这个 Home.vue 主要是用来完成页面的大框架结构。

TreeView.vue

<template>
  <div class="tree-view-menu">
      <Tree-view-item :menus='menus'></Tree-view-item>
  </div>
</template>
<script>
import TreeViewItem from "./TreeViewItem";
const menusData = [];
export default {
  components: {
    TreeViewItem
  },
  name: "TreeViewMenu",
  data() {
    return {
      menus: this.$store.state.menusModule.menus
    };
  }
};
</script>
<style scoped>
.tree-view-menu {
  width: 300px;
  height: 100%;
  overflow-y: auto;
  overflow-x: hidden;
}
.tree-view-menu::-webkit-scrollbar {
  height: 6px;
  width: 6px;
}
.tree-view-menu::-webkit-scrollbar-trac {
  -webkit-box-shadow: inset 0 0 6px rgba(0, 0, 0, 0.3);
  box-shadow: inset 0 0 6px rgba(0, 0, 0, 0.3);
}
.tree-view-menu::-webkit-scrollbar-thumb {
  background-color: #6e6e6e;
  outline: 1px solid #333;
}
.tree-view-menu::-webkit-scrollbar {
  height: 4px;
  width: 4px;
}
.tree-view-menu::-webkit-scrollbar-track {
  -webkit-box-shadow: inset 0 0 6px rgba(0, 0, 0, 0.3);
  box-shadow: inset 0 0 6px rgba(0, 0, 0, 0.3);
}
.tree-view-menu::-webkit-scrollbar-thumb {
  background-color: #6e6e6e;
  outline: 1px solid #708090;
}
</style>

这个组件也非常地简单，拿到菜单数据，传给子组件，并把菜单的滚动条样式修改了下。

TreeViewItem.vue

<template>
  <div class="tree-view-item">
    <div class="level" :class="'level-'+ menu.level" v-for="menu in menus" :key="menu.id">
      <div v-if="menu.type === 'link'">
        <router-link class="link" v-bind:to="menu.url" @click.native="toggle(menu)">{{menu.name}}</router-link>
      </div>
      <div v-if="menu.type === 'button'">
        <div class="button heading" :class="{selected: menu.isSelected,expand:menu.isExpanded}" @click="toggle(menu)">
          {{menu.name}}
          <div class="icon">
            <svg xmlns="http://www.w3.org/2000/svg" focusable="false" viewBox="0 0 24 24">
              <path d="M8.59 16.34l4.58-4.59-4.58-4.59L10 5.75l6 6-6 6z "></path>
            </svg>
          </div>
        </div>
         <transition name="fade">
          <div class="heading-children" v-show="menu.isExpanded" v-if="menu.subMenu">
            <Tree-view-item :menus='menu.subMenu'></Tree-view-item>
          </div>
        </transition>
      </div>
    </div>
  </div>
</template>
<script>
export default {
  name: "TreeViewItem",
  props: ["menus"],
  created() {
    this.$store.commit("firstInit", { url: this.$route.path });
  },
  methods: {
    toggle(menu) {
      this.$store.commit("findParents", { menu });
    }
  }
};
</script>
<style scoped>
a {
  text-decoration: none;
  color: #333;
}
.link,
.button {
  display: block;
  padding: 10px 15px;
  transition: background-color 0.2s ease-in-out 0s, color 0.3s ease-in-out 0.1s;
  -moz-user-select: none;
  -webkit-user-select: none;
  -ms-user-select: none;
  -khtml-user-select: none;
  user-select: none;
}
.button {
  position: relative;
}
.link:hover,
.button:hover {
  color: #1976d2;
  background-color: #eee;
  cursor: pointer;
}
.icon {
  position: absolute;
  right: 0;
  display: inline-block;
  height: 24px;
  width: 24px;
  fill: currentColor;
  transition: -webkit-transform 0.15s;
  transition: transform 0.15s;
  transition: transform 0.15s, -webkit-transform 0.15s;
  transition-timing-function: ease-in-out;
}
.heading-children {
  padding-left: 14px;
  overflow: hidden;
}
.expand {
  display: block;
}
.collapsed {
  display: none;
}
.expand .icon {
  -webkit-transform: rotate(90deg);
  transform: rotate(90deg);
}
.selected {
  color: #1976d2;
}
.fade-enter-active {
  transition: all 0.5s ease 0s;
}
.fade-enter {
  opacity: 0;
}
.fade-enter-to {
  opacity: 1;
}
.fade-leave-to {
  height: 0;
}
</style>

上面的这个组件才是这个树型结构重点代码，用了递归的思想来实现这个树型菜单。

TreeViewDetail.vue

<template>
    <h3>
        这里是{{currentRoute}}导航详情
    </h3>
</template>
<script>
export default {
  name: "TreeViewDetail",
  data() {
    return {
      currentRoute: this.$route.path
    };
  },
  watch: {
    //监听路由，只要路由有变化(路径，参数等变化)都有执行下面的函数
    $route: {
      handler: function(val, oldVal) {
        this.currentRoute = val.name;
      },
      deep: true
    }
  }
};
</script>
<style scoped>
h3 {
  margin-top: 10px;
  font-weight: normal;
}
</style>

router/index.js

import Vue from 'vue';
import Router from 'vue-router';
import App from '@/components/App';
import TreeViewDetail from '@/components/TreeViewDetail';
Vue.use(Router)
export default new Router({
  linkActiveClass: 'selected',
  routes: [{
      path: '/',
      name: 'App',
      component: App
    },
    {
      path: '/detail/quickstart',
      name: 'quickstart',
      component: TreeViewDetail
    },
    {
      path: '/detail/tutorial',
      name: 'tutorial',
      component: TreeViewDetail
    },
    {
      path: '/detail/toh-pt1',
      name: 'toh-pt1',
      component: TreeViewDetail
    },
    {
      path: '/detail/toh-pt2',
      name: 'toh-pt2',
      component: TreeViewDetail
    },
    {
      path: '/detail/toh-pt3',
      name: 'toh-pt3',
      component: TreeViewDetail
    },
    {
      path: '/detail/toh-pt4',
      name: 'toh-pt4',
      component: TreeViewDetail
    },
    {
      path: '/detail/toh-pt5',
      name: 'toh-pt5',
      component: TreeViewDetail
    },
    {
      path: '/detail/toh-pt6',
      name: 'toh-pt6',
      component: TreeViewDetail
    },
    {
      path: '/detail/architecture',
      name: 'architecture',
      component: TreeViewDetail
    },
    {
      path: '/detail/displaying-data',
      name: 'displaying-data',
      component: TreeViewDetail
    },
    {
      path: '/detail/template-syntax',
      name: 'template-syntax',
      component: TreeViewDetail
    },
    {
      path: '/detail/lifecycle-hooks',
      name: 'lifecycle-hooks',
      component: TreeViewDetail
    },
    {
      path: '/detail/component-interaction',
      name: 'component-interaction',
      component: TreeViewDetail
    },
    {
      path: '/detail/component-styles',
      name: 'component-styles',
      component: TreeViewDetail
    },
    {
      path: '/detail/dynamic-component-loader',
      name: 'dynamic-component-loader',
      component: TreeViewDetail
    },
    {
      path: '/detail/attribute-directives',
      name: 'attribute-directives',
      component: TreeViewDetail
    },
    {
      path: '/detail/structural-directives',
      name: 'structural-directives',
      component: TreeViewDetail
    },
    {
      path: '/detail/pipes',
      name: 'pipes',
      component: TreeViewDetail
    },
    {
      path: '/detail/animations',
      name: 'animations',
      component: TreeViewDetail
    },
    {
      path: '/detail/user-input',
      name: 'user-input',
      component: TreeViewDetail
    },
    {
      path: '/detail/forms',
      name: 'forms',
      component: TreeViewDetail
    },
    {
      path: '/detail/form-validation',
      name: 'form-validation',
      component: TreeViewDetail
    },
    {
      path: '/detail/reactive-forms',
      name: 'reactive-forms',
      component: TreeViewDetail
    },
    {
      path: '/detail/dynamic-form',
      name: 'dynamic-form',
      component: TreeViewDetail
    },
    {
      path: '/detail/bootstrapping',
      name: 'bootstrapping',
      component: TreeViewDetail
    },
    {
      path: '/detail/ngmodule',
      name: 'ngmodule',
      component: TreeViewDetail
    },
    {
      path: '/detail/ngmodule-faq',
      name: 'ngmodule-faq',
      component: TreeViewDetail
    },
    {
      path: '/detail/dependency-injection',
      name: 'dependency-injection',
      component: TreeViewDetail
    },
    {
      path: '/detail/hierarchical-dependency-injection',
      name: 'hierarchical-dependency-injection',
      component: TreeViewDetail
    },
    {
      path: '/detail/dependency-injection-in-action',
      name: 'dependency-injection-in-action',
      component: TreeViewDetail
    },
    {
      path: '/detail/http',
      name: 'http',
      component: TreeViewDetail
    },
    {
      path: '/detail/router',
      name: 'router',
      component: TreeViewDetail
    },
    {
      path: '/detail/testing',
      name: 'testing',
      component: TreeViewDetail
    },
    {
      path: '/detail/cheatsheet',
      name: 'cheatsheet',
      component: TreeViewDetail
    },
    {
      path: '/detail/i18n',
      name: 'i18n',
      component: TreeViewDetail
    },
    {
      path: '/detail/language-service',
      name: 'language-service',
      component: TreeViewDetail
    },
    {
      path: '/detail/security',
      name: 'security',
      component: TreeViewDetail
    },
    {
      path: '/detail/setup',
      name: 'setup',
      component: TreeViewDetail
    },
    {
      path: '/detail/setup-systemjs-anatomy',
      name: 'setup-systemjs-anatomy',
      component: TreeViewDetail
    },
    {
      path: '/detail/browser-support',
      name: 'browser-support',
      component: TreeViewDetail
    },
    {
      path: '/detail/npm-packages',
      name: 'npm-packages',
      component: TreeViewDetail
    },
    {
      path: '/detail/typescript-configuration',
      name: 'typescript-configuration',
      component: TreeViewDetail
    },
    {
      path: '/detail/aot-compiler',
      name: 'aot-compiler',
      component: TreeViewDetail
    },
    {
      path: '/detail/metadata',
      name: 'metadata',
      component: TreeViewDetail
    },
    {
      path: '/detail/deployment',
      name: 'deployment',
      component: TreeViewDetail
    },
    {
      path: '/detail/upgrade',
      name: 'upgrade',
      component: TreeViewDetail
    },
    {
      path: '/detail/ajs-quick-reference',
      name: 'ajs-quick-reference',
      component: TreeViewDetail
    },
    {
      path: '/detail/visual-studio-2015',
      name: 'visual-studio-2015',
      component: TreeViewDetail
    },
    {
      path: '/detail/styleguide',
      name: 'styleguide',
      component: TreeViewDetail
    },
    {
      path: '/detail/glossary',
      name: 'glossary',
      component: TreeViewDetail
    },
    {
      path: '/detail/api',
      name: 'api',
      component: TreeViewDetail
    }
  ]
})

store/module/menusModule.js

let menus = [
  { id: 1, level: 1, name: '快速上手', type: "link", url: "/detail/quickstart" },
  {
    id: 2,
    level: 1,
    name: '教程',
    type: "button",
    isExpanded: false,
    isSelected: false,
    subMenu: [
      { id: 21, level: 2, name: '简介', type: "link", url: "/detail/tutorial" },
      { id: 22, level: 2, name: '英雄编辑器', type: "link", url: "/detail/toh-pt1" },
      { id: 23, level: 2, name: '主从结构', type: "link", url: "/detail/toh-pt2" },
      { id: 24, level: 2, name: '多个组件', type: "link", url: "/detail/toh-pt3" },
      { id: 25, level: 2, name: '服务', type: "link", url: "/detail/toh-pt4" },
      { id: 26, level: 2, name: '路由', type: "link", url: "/detail/toh-pt5" },
      { id: 27, level: 2, name: 'HTTP', type: "link", url: "/detail/toh-pt6" },
    ]
  },
  {
    id: 3,
    level: 1,
    name: '核心知识',
    type: "button",
    isExpanded: false,
    isSelected: false,
    subMenu: [
      { id: 31, level: 2, name: '架构', type: "link", url: "/detail/architecture" },
      {
        id: 32,
        level: 2,
        name: '模板与数据绑定',
        type: "button",
        isExpanded: false,
        isSelected: false,
        subMenu: [
          { id: 321, level: 3, name: '显示数据', type: "link", url: "/detail/displaying-data" },
          { id: 322, level: 3, name: '模板语法', type: "link", url: "/detail/template-syntax" },
          { id: 323, level: 3, name: '生命周期钩子', type: "link", url: "/detail/lifecycle-hooks" },
          { id: 324, level: 3, name: '组件交互', type: "link", url: "/detail/component-interaction" },
          { id: 325, level: 3, name: '组件样式', type: "link", url: "/detail/component-styles" },
          { id: 326, level: 3, name: '动态组件', type: "link", url: "/detail/dynamic-component-loader" },
          { id: 327, level: 3, name: '属性型指令', type: "link", url: "/detail/attribute-directives" },
          { id: 328, level: 3, name: '结构型指令', type: "link", url: "/detail/structural-directives" },
          { id: 329, level: 3, name: '管道', type: "link", url: "/detail/pipes" },
          { id: 3210, level: 3, name: '动画', type: "link", url: "/detail/animations" },
        ]
      },
      {
        id: 33,
        level: 2,
        name: '表单',
        type: "button",
        isExpanded: false,
        isSelected: false,
        subMenu: [
          { name: '用户输入', type: "link", url: "/detail/user-input" },
          { name: '模板驱动表单', type: "link", url: "/detail/forms" },
          { name: '表单验证', type: "link", url: "/detail/form-validation" },
          { name: '响应式表单', type: "link", url: "/detail/reactive-forms" },
          { name: '动态表单', type: "link", url: "/detail/dynamic-form" }
        ]
      },
      { id: 34, level: 2, name: '引用启动', type: "link", url: "/detail/bootstrapping" },
      {
        id: 35,
        level: 2,
        name: 'NgModules',
        type: "button",
        isExpanded: false,
        isSelected: false,
        subMenu: [
          { id: 341, level: 3, name: 'NgModule', type: "link", url: "/detail/ngmodule" },
          { id: 342, level: 3, name: 'NgModule 常见问题', type: "link", url: "/detail/ngmodule-faq" }
        ]
      },
      {
        id: 36,
        level: 2,
        name: '依赖注入',
        type: "button",
        isExpanded: false,
        isSelected: false,
        subMenu: [
          { id: 361, level: 3, name: '依赖注入', type: "link", url: "/detail/dependency-injection" },
          { id: 362, level: 3, name: '多级注入器', type: "link", url: "/detail/hierarchical-dependency-injection" },
          { id: 363, level: 3, name: 'DI 实例技巧', type: "link", url: "/detail/dependency-injection-in-action" }
        ]
      },
      { id: 37, level: 2, name: 'HttpClient', type: "link", url: "/detail/http" },
      { id: 38, level: 2, name: '路由与导航', type: "link", url: "/detail/router" },
      { id: 39, level: 2, name: '测试', type: "link", url: "/detail/testing" },
      { id: 310, level: 2, name: '速查表', type: "link", url: "/detail/cheatsheet" },
    ]
  },
  {
    id: 4,
    level: 1,
    name: '其它技术',
    type: "button",
    isExpanded: false,
    isSelected: false,
    subMenu: [
      { id: 41, level: 2, name: '国际化（i18n）', type: "link", url: "/detail/i18n" },
      { id: 42, level: 2, name: '语言服务', type: "link", url: "/detail/language-service" },
      { id: 43, level: 2, name: '安全', type: "link", url: "/detail/security" },
      {
        id: 44,
        level: 2,
        name: '环境设置与部署',
        type: "button",
        isExpanded: false,
        isSelected: false,
        subMenu: [
          { id: 441, level: 3, name: '搭建本地开发环境', type: "link", url: "/detail/setup" },
          { id: 442, level: 3, name: '搭建方式剖析', type: "link", url: "/detail/setup-systemjs-anatomy" },
          { id: 443, level: 3, name: '浏览器支持', type: "link", url: "/detail/browser-support" },
          { id: 444, level: 3, name: 'npm 包', type: "link", url: "/detail/npm-packages" },
          { id: 445, level: 3, name: 'TypeScript 配置', type: "link", url: "/detail/typescript-configuration" },
          { id: 446, level: 3, name: '预 (AoT) 编译器', type: "link", url: "/detail/aot-compiler" },
          { id: 447, level: 3, name: '预 (AoT) 编译器', type: "link", url: "/detail/metadata" },
          { id: 448, level: 3, name: '部署', type: "link", url: "/detail/deployment" }
        ]
      },
      {
        id: 45,
        level: 2,
        name: '升级',
        type: "button",
        isExpanded: false,
        isSelected: false,
        subMenu: [
          { id: 451, level: 3, name: '从 AngularJS 升级', type: "link", url: "/detail/upgrade" },
          { id: 452, level: 3, name: '升级速查表', type: "link", url: "/detail/ajs-quick-reference" }
        ]
      },
      { id: 46, level: 2, name: 'Visual Studio 2015 快速上手', type: "link", url: "/detail/visual-studio-2015" },
      { id: 47, level: 2, name: '风格指南', type: "link", url: "/detail/styleguide" },
      { id: 48, level: 2, name: '词汇表', type: "link", url: "/detail/glossary" }
    ]
  },
  { id: 5, level: 1, name: 'API 参考手册', type: "link", url: "/detail/api" }
];
let levelNum = 1;
let startExpand = []; // 保存刷新后当前要展开的菜单项
function setExpand(source, url) {
  let sourceItem = '';
  for (let i = 0; i < source.length; i++) {
    sourceItem = JSON.stringify(source[i]); // 把菜单项转为字符串
    if (sourceItem.indexOf(url) > -1) { // 查找当前 URL 所对应的子菜单属于哪一个祖先菜单
      if (source[i].type === 'button') { // 导航菜单为按钮
        source[i].isSelected = true; // 设置选中高亮
        source[i].isExpanded = true; // 设置为展开
        startExpand.push(source[i]);
        // 递归下一级菜单，以此类推
        setExpand(source[i].subMenu, url);
      }
      break;
    }
  }
}
const state = {
  menus,
  levelNum
};
const mutations = {
  findParents(state, payload) {
    if (payload.menu.type === "button") {
      payload.menu.isExpanded = !payload.menu.isExpanded;
    } else if (payload.menu.type === "link") {
      if (startExpand.length > 0) {
        for (let i = 0; i < startExpand.length; i++) {
          startExpand[i].isSelected = false;
        }
      }
      startExpand = []; // 清空展开菜单记录项
      setExpand(state.menus, payload.menu.url);
    };
  },
  firstInit(state, payload) {
    setExpand(state.menus, payload.url);
  }
}
export default {
  state,
  mutations
};

在使用状态管理时，我们一定要记住，一旦数据写到了 state 中时，就不能再添加其它属性了，什么时间？就拿上面的 menus 数据来说，比如，本来菜单数据中没有 isExpanded 这个字段的,然后你在 mutations 的方法中给 menus 对象添加了一个 isExpanded 属性，但你会发现属性是不会被状态管理追踪到的，所以我们一开始就给这个数据添加了 isExpanded 和 isSelected 。

store/index.js

import Vue from 'vue'
import Vuex from 'vuex'
import menusModule from './module/menusModule'
Vue.use(Vuex);
const store = new Vuex.Store({
  modules: {
    menusModule
  }
})
export default store;

上面这个例子在使用状态管理时，把菜单的相关配置封装成模块，然后再引入。如果把状态管理写成模块的形式的话，在调用这个模块中的状态时就需要注意了，写法可以参数示例中的代码。

上面这个例子可以直接用到自己的项目中，只要你理解了其中的思想，其他的都不是问题。Vue 实现树形菜单功能模块之旅只能带你到这里了。