vue递归组件：树形控件

1、递归组件-简单树形控件预览及问题

在编写树形组件时遇到的问题：

• 组件如何才能递归调用？
• 递归组件点击事件如何传递？

2、树形控件基本结构及样式

<template>
  <ul class="vue-tree">
    <li class="tree-item">
      <div class="tree-content">
        <div class="expand-arrow">div>
        <div class="tree-label">小学div>
      div>
      <ul class="sub-tree">
        <li class="tree-item expand">
          <div class="tree-content">
            <div class="expand-arrow">div>
            <div class="tree-label">语文div>
          div>
        li>
        <li class="tree-item">
          <div class="tree-content">
            <div class="expand-arrow">div>
            <div class="tree-label">数学div>
          div>
        li>
      ul>
    li>
  ul>
template>

<style lang="stylus">
.vue-tree{
  list-style: none;
  padding: 0;
  margin: 0;
  .tree-item{
    cursor: pointer;
    transition: background-color .2s;
    .tree-content{
      position: relative;
      padding-left: 28px;
      &:hover{
        background-color: #f0f7ff;
      }
    }
    .expand-arrow{
      position: absolute;
      top: 0;
      left: 0;
      width: 28px;
      height: 28px;
      cursor: pointer;
      &::after{
        position: absolute;
        top: 50%;
        left: 50%;
        display: block;
        content: ' ';
        border-width: 5px;
        border-style: solid;
        border-color: transparent;
        border-left-color: #ccc;
        margin: -5px 0 0 -2.5px;
        transition: all .2s;
      }
    }
    &.expand{
      &>.tree-content{
        background-color: #f0f7ff;
        &>.expand-arrow{
          &::after{
            transform: rotate(90deg);
            margin: -2.5px 0 0 -5px;
          }
        }
      }
    }
    .tree-label{
      height: 28px;
      line-height: 28px;
      font-size: 14px;
    }
    .sub-tree{
      display: none;
      list-style: none;
      padding: 0 0 0 28px;
      margin: 0;
    }
    &.expand>.sub-tree{
      display: block;
    }
    &.no-child{
      &>.tree-content{
        &>.expand-arrow{
          display: none;
        }
      }
    }
  }
}
style>

3、组件目录及数据结构

目录结构
vue-tree

• VueTree.vue 树形控件父组件
• TreeItem.vue 树形控件递归组件

树形控件数据结构

let treeData = [
  {
    text: "一级", // 显示的文字
    expand: false, // 默认是否展开
    children: [ // 子节点
      {
        text: "一级-1",
        expand: false,
      },
      {
        text: "一级-2",
        expand: false,
        children: [
          {
            text: "一级-2-1",
            expand: false,
          },
          {
            text: "一级-2-2",
            expand: false,
          }
        ]
      }
    ]
  }
];

3.1、TreeItem.vue 代码

<template>
  <li class="tree-item" :class="{expand: isExpand, 'no-child': !treeItemData.children || treeItemData.children.length  === 0}">
    <div class="tree-content" @click="_clickEvent">
      <div class="expand-arrow" @click.stop="expandTree()">div>
      <div class="tree-label">{{treeItemData.text}}div>
    div>
    <ul class="sub-tree" v-if="treeItemData.children && treeItemData.children.length > 0">
      
      <TreeItem
        v-for="item in treeItemData.children"
        :tree-item-data="item"
        :key="uuid()"
        :tree-click-event="treeClickEvent">TreeItem>
    ul>
  li>
template>

<script>
  export default {
    name: "TreeItem",
    props: {
      treeItemData: {
        type: Object,
        default(){
          return {};
        }
      },
      // 节点点击事件
      treeClickEvent: {
        type: Function,
        default() {
          return function () {};
        }
      }
    },
    data(){
      return {
        // 节点是否展开
        isExpand: this.treeItemData.expand || false
      }
    },
    methods: {
      // 展开/收缩
      expandTree(flag){
        if(!this.treeItemData.children || this.treeItemData.children.length === 0){
          return;
        }
        if(typeof flag === 'undefined'){
          flag = !this.isExpand;
        }else{

          flag = !!flag;
        }
        this.isExpand = flag;
      },
      // 创建一个唯一id
      uuid(){
        let str = Math.random().toString(32);
        str = str.substr(2);
        return str;
      },
      // 节点点击事件
      _clickEvent(){
        // 如果有传递事件函数，则调用事件函数并传递当前节点数据及组件
        if(this.treeClickEvent && typeof this.treeClickEvent === 'function'){
          this.treeClickEvent(this.treeItemData, this);
        }
      }
    }
  }
script>

3.1.1、解决 组件如何才能递归调用？ 问题

在组件模板内调用自身必须明确定义组件的name属性，并且递归调用时组件名称就是name属性。如在TreeItem.vue组件中组件的name名称为'TreeItem'，那么在template中调用时组件名称就必须是。
当然也可以全局注册组件，具体可以查看vue官方文档 递归组件

3.1.2、解决 递归组件点击事件如何传递？ 问题

我这里的解决方案是使用props将事件函数传递进来，在点击节点的时候调用事件函数，并把相应的数据传递进去。
之前也尝试过使用$emit的形式并把数据传递过去，由于是递归组件，这样一直$emit，到最外层时传递的数据就变了，比如传递是第3层节点的数据，到最后执行时数据就变成第1层节点的数据了

4、VueTree.vue 组件

<template>
  <ul class="vue-tree">
    <TreeItem
        v-for="(item, index) in treeData"
        :key="index"
        :treeItemData="item"
        :tree-click-event="treeClickEvent">TreeItem>
  ul>
template>

<script>
  import TreeItem from "./TreeItem";
  export default {
    name: "VueTreeMenu",
    components: {
      TreeItem
    },
    props: {
     // 树形控件数据
      treeData: {
        type: Array,
        default(){
          return [];
        }
      },
      // 节点点击事件
      treeClickEvent: {
        type: Function,
        default() {
          return function () {};
        }
      }
    }
  }
script>

<style lang="stylus">
.vue-tree{
  list-style: none;
  padding: 0;
  margin: 0;
  .tree-item{
    cursor: pointer;
    transition: background-color .2s;
    .tree-content{
      position: relative;
      padding-left: 28px;
      &:hover{
        background-color: #f0f7ff;
      }
    }
    .expand-arrow{
      position: absolute;
      top: 0;
      left: 0;
      width: 28px;
      height: 28px;
      cursor: pointer;
      &::after{
        position: absolute;
        top: 50%;
        left: 50%;
        display: block;
        content: ' ';
        border-width: 5px;
        border-style: solid;
        border-color: transparent;
        border-left-color: #ccc;
        margin: -5px 0 0 -2.5px;
        transition: all .2s;
      }
    }
    &.expand{
      &>.tree-content{
        background-color: #f0f7ff;
        &>.expand-arrow{
          &::after{
            transform: rotate(90deg);
            margin: -2.5px 0 0 -5px;
          }
        }
      }
    }
    .tree-label{
      height: 28px;
      line-height: 28px;
      font-size: 14px;
    }
    .sub-tree{
      display: none;
      list-style: none;
      padding: 0 0 0 28px;
      margin: 0;
    }
    &.expand>.sub-tree{
      display: block;
    }
    &.no-child{
      &>.tree-content{
        /*padding-left: 0;*/
        &>.expand-arrow{
          display: none;
        }
      }
    }
  }
}
style>

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5、使用树形组件

<template>
  <div class="app" id="app">
    <VueTree :tree-data="treeData2" :tree-click-event="treeClickEvent">VueTree>
  div>
template>

<script>
import VueTree from "./components/vue-tree/VueTree";

export default {
  name: 'app',
  data(){
    return {
      treeData2: [
        {
          text: "一级", // 显示的文字
          expand: false, // 默认是否展开
          children: [
            {
              text: "二级-1",
              expand: false,
            },
            {
              text: "二级-2",
              expand: false,
              children: [
                {
                  text: "三级-1",
                  expand: false,
                },
                {
                  text: "三级-2",
                  expand: false,
                  children: [
                    {
                      text: "四级-1",
                      expand: false,
                    }
                  ]
                }
              ]
            }
          ]
        },
        {
          text: "一级-2",
          expand: false
        }
      ]
    }
  },
  methods: {
    treeClickEvent(item, treeItem){
      console.log(item);
    }
  },
  components: {
    VueTree
  }
}
script>