1.组件调用代码

<template>
  <div id="app">
    <h1>{{`基于Element-UI组件改造的树形选择器`}}:</h1>
    <!-- 调用树形下拉框组件 -->
    <!-- 下拉树 -->
    <selectbutton
      :props="props"
      :options="optionData"
      :value="valueId"
      :clearable="isClearable"
      :accordion="isAccordion"
      @getValue="getValue($event)"
      height="200"
    ></selectbutton>
    ID为：{{valueId}}
  </div>
</template>

调用组件的数据

<script>
import SelectTree from "./components/treeSelect.vue";
export default {
  name: "app",
  components: {
    SelectTree
  },
  data() {
    return {
      isClearable: true, // 可清空（可选）
      isAccordion: true, // 可收起（可选）
      valueId: 1, // 初始ID（可选）
      props: {
        // 配置项（必选）
        value: "id",
        label: "name",
        children: "children"
        // disabled:true
      },
      // 选项列表（必选）
      list: [
        { id: 1, parentId: 0, name: "一级菜单A", rank: 1 },
        { id: 2, parentId: 0, name: "一级菜单B", rank: 1 },
        { id: 3, parentId: 0, name: "一级菜单C", rank: 1 },
        { id: 4, parentId: 1, name: "二级菜单A-A", rank: 2 },
        { id: 5, parentId: 1, name: "二级菜单A-B", rank: 2 },
        { id: 6, parentId: 2, name: "二级菜单B-A", rank: 2 },
        { id: 7, parentId: 4, name: "三级菜单A-A-A", rank: 3 },
        { id: 8, parentId: 7, name: "四级菜单A-A-A-A", rank: 4 },
        { id: 9, parentId: 0, name: "一级菜单C", rank: 1 },
        { id: 10, parentId: 0, name: "一级菜单end", rank: 1 }
      ],
    };
  },
  computed: {
    /* 转树形数据 */
    optionData() {
      let cloneData = JSON.parse(JSON.stringify(this.list)); // 对源数据深度克隆
      return cloneData.filter(father => {
        // 循环所有项，并添加children属性
        let branchArr = cloneData.filter(child => father.id == child.parentId); // 返回每一项的子级数组
        branchArr.length > 0 ? (father.children = branchArr) : ""; //给父级添加一个children属性，并赋值
        return father.parentId == 0; //返回第一层
      });
    }
  },
  methods: {
    // 取值
    getValue(value) {
      this.valueId = value;
      console.log(this.valueId);
    }
  }
};
</script>

2.组件封装

<template>
  <el-select :value="valueTitle" :clearable="clearable" @clear="clearHandle"  ref="treeSelect">
    <el-input
      class="selectInput"
      :placeholder="placeholder"
      v-model="filterText">
    </el-input>

    <el-option :value="valueTitle" :label="valueTitle" class="options">
      <el-tree  id="tree-option"
        ref="selectTree"
        :accordion="accordion"
        :data="options"
        :props="props"
        :node-key="props.value"    
        :default-expanded-keys="defaultExpandedKey"
        :filter-node-method="filterNode"
        @node-click="handleNodeClick">
      </el-tree>
    </el-option>
  </el-select>
</template>

<script>
export default {
  name: "el-tree-select",
  props:{
    /* 配置项 */
    props:{
      type: Object,
      default:()=>{
        return {
          value:'id',             // ID字段名
          label: 'title',         // 显示名称
          children: 'children'    // 子级字段名
        }
      }
    },
    /* 选项列表数据(树形结构的对象数组) */
    options:{
      type: Array,       
      default: ()=>{ return [] }
    },
    /* 初始值 */
    value:{
      type: Number,
      default: ()=>{ return null }
    },
    /* 可清空选项 */
    clearable:{
      type:Boolean,
      default:()=>{ return true }
    },
    /* 自动收起 */
    accordion:{
      type:Boolean,
      default:()=>{ return false }
    },
    placeholder:{
      type:String,
      default:()=>{return "检索关键字"}
    }
  },
  data() {
    return {
      filterText: '',
      valueId:this.value,    // 初始值
      valueTitle:'',
      defaultExpandedKey:[]    
    }
  },
  mounted(){
    this.initHandle()
  },
  methods: {
    // 初始化值
    initHandle(){
      if(this.valueId){
        this.valueTitle = this.$refs.selectTree.getNode(this.valueId).data[this.props.label]     // 初始化显示
        this.$refs.selectTree.setCurrentKey(this.valueId)       // 设置默认选中
        this.defaultExpandedKey = [this.valueId]      // 设置默认展开
      } 
      this.initScroll()
    },
    // 初始化滚动条
    initScroll(){
      this.$nextTick(()=>{
        let scrollWrap = document.querySelectorAll('.el-scrollbar .el-select-dropdown__wrap')[0]
        let scrollBar = document.querySelectorAll('.el-scrollbar .el-scrollbar__bar')
        scrollWrap.style.cssText = 'margin: 0px; max-height: none; overflow: hidden;'
        scrollBar.forEach(ele => ele.style.width = 0)
      })
    },
    // 切换选项
    handleNodeClick(node){
      this.valueTitle = node[this.props.label]
      this.valueId = node[this.props.value]
      this.$emit('getValue',this.valueId)
      this.defaultExpandedKey = []
      if(!node.children || !node.children.length) { //补录选择完选项弹框不能收起
        this.$refs.treeSelect.blur()
      }
    },
    // 清除选中
    clearHandle(){
      this.valueTitle = ''
      this.valueId = null
      this.defaultExpandedKey = []
      this.clearSelected()
      this.$emit('getValue',null)
    },
    /* 清空选中样式 */
    clearSelected(){
      let allNode = document.querySelectorAll('#tree-option .el-tree-node')
      allNode.forEach((element)=>element.classList.remove('is-current'))
    },
    filterNode(value, data) {
      if (!value) return true;
      return data.name.indexOf(value) !== -1;
    }
  },
  watch: {
    value(){
      this.valueId = this.value
      this.initHandle()
    },
    filterText(val) {
      this.$refs.selectTree.filter(val);
    }
  },
};
</script>

3.样式修改

<!-- Add "scoped" attribute to limit CSS to this component only -->
<style scoped>
  .el-scrollbar .el-scrollbar__view .el-select-dropdown__item{
    height: auto;
    max-height: 274px;
    padding: 0;
    overflow: hidden;
    overflow-y: auto;
  }
  .el-select-dropdown__item.selected{
    font-weight: normal;
  }
  ul li >>>.el-tree .el-tree-node__content{
    height:auto;
    padding: 0 20px;
  }
  .el-tree-node__label{
    font-weight: normal;
  }
  .el-tree >>>.is-current .el-tree-node__label{
    color: #409EFF;
    font-weight: 700;
  }
  .el-tree >>>.is-current .el-tree-node__children .el-tree-node__label{
    color:#606266;
    font-weight: normal;
  }
  .selectInput{
    padding: 0 5px;
    box-sizing: border-box;
  }
</style>