vue项目使用组件库是element-ui，涉及到的组件库组件有 Tree 树形控件、Icon 图标
样式如下图

下拉选择框-勾选树形结构数据

具体代码

<template>
<div class="customize-tree" ref="targetBlock">
  <div class="floating-box" :style="`bottom: ${chunkHeight}px; display: ${selectGroupShow};`" >
    <el-tree
      ref="cognitiveGoalsTree"
      :data="CognitiveGoalsOptions"
      show-checkbox
      node-key="value"
      @check="handleCheckChange"
      :props="defaultProps">
    </el-tree>
  </div>
  <div class="select-data-group" v-if="checkedNodes.length>0" ref="variableHeightBlock" @click="selectDataGroup">
    <span v-for="(item,index) in checkedNodes" :key="index" class="item">
      <span v-if="item.fName">{{ item.fName + '/' + item.label }}</span>
      <span v-else>{{ item.label }}</span>
      <i class="el-icon-error" @click.stop="deleteCheckedNode(index)"></i>
    </span>
    <div class="right-icon right-icon1" :style="`top: ${chunkHeight/2-14}px;`">
      <i v-if="selectGroupShow == 'none'" class="el-icon-arrow-down"></i>
      <i v-else class="el-icon-arrow-up"></i>
      <i class="el-icon-error" @click.stop="deleteCheckedNode(0,'del')"></i>
    </div>
  </div>
  <div class="select-data-group" v-else ref="variableHeightBlock" @click="selectDataGroup">
    <span class="placeholder-text">请选择知识点</span>
    <div class="right-icon" >
      <i v-if="selectGroupShow == 'none'" class="el-icon-arrow-down"></i>
      <i v-else class="el-icon-arrow-up"></i>
    </div>
  </div>
</div>
</template>

js

data(){
  return {
      CognitiveGoalsOptions: [], // 知识点+认知目标三级列表
      CognitiveGoalsValue: [], // 选中的认知目标 三级列表选中项
      defaultProps: {
        children: 'children',
        label: 'label'
      },
      checkedNodes: [], // 树形结构选中的数据 
      chunkHeight: 52,// 获取块的高度
      selectGroupShow: 'none', // 隐藏
  }
}
mounted () {
    // 监听点击事件
    document.addEventListener('click', this.handleClickOutside);
},
beforeDestroy(){
    // 卸载点击事件
    document.removeEventListener('click', this.handleClickOutside);
},
methods: {
    // 点击事件
    selectDataGroup() {
      this.selectGroupShow = this.selectGroupShow == 'none' ? 'block' : 'none'
    },
    handleCheckChange(e, data) {
      if (data.checkedNodes && data.checkedNodes.length > 0) {
        let arr = []
        data.checkedNodes.forEach(ele => {
          if (ele.children && ele.children.length>0) {
          } else {
            arr.push(ele)
            this.CognitiveGoalsValue.push(ele.value)
          }
        });
        this.checkedNodes = arr
      } else {
        this.checkedNodes = []
        this.CognitiveGoalsValue = []
      }
      this.$nextTick(() => {
        this.getBlockHeight();
      });
    },
    getBlockHeight() {
      if (this.$refs.variableHeightBlock) {
        this.chunkHeight = this.$refs.variableHeightBlock.offsetHeight + 12;
      }
    },
    deleteCheckedNode(index,str) {
      let arr = []
      this.CognitiveGoalsValue = []
      if (str == 'del') {
        this.checkedNodes = []
      } else {
        this.checkedNodes.splice(index,1)
        this.checkedNodes.forEach(ele => {
          arr.push(ele.value)
        })
      }
      this.CognitiveGoalsValue = arr
      this.$refs.cognitiveGoalsTree.setCheckedKeys(arr);
      this.$nextTick(() => {
        this.getBlockHeight();
      });
    },
    handleClickOutside(event) {
      const targetBlock = this.$refs.targetBlock;
      if (!targetBlock.contains(event.target)) {
        this.selectGroupShow = 'none'
      }
    },
}

css

.customize-tree{
  position: relative;
  .select-data-group{
    width: 430px;
    padding: 4px 0;
    min-height: 38px;
    border: 1px solid #DCDFE6;
    border-radius: 4px;
    display: flex;
    flex-wrap: wrap;
    position: relative;
    &:hover{
      border-color: #c0c4cc;
    }
    .placeholder-text{
      height: 30px;
      line-height: 30px;
      display: inline-block;
      font-size: 14px;
      color: #c0c4cc;
      padding-left: 14px;
    }
    .right-icon{
      color: #c0c4cc;
      position: absolute;
      right: 8px;
      top: 10px;
    }
    .right-icon1{
      .el-icon-error{
        display: none;
      }
      &:hover{
        .el-icon-arrow-down{
          display: none;
        }
        .el-icon-arrow-up{
          display: none;
        }
        .el-icon-error{
          display: inline-block;
        }
      }
    }
    .item{
      max-width: calc(100% - 35px);
      display: inline-block;
      background-color: #f4f4f5;
      border-color: #e9e9eb;
      border-radius: 4px;
      color: #909399;
      margin: 2px 0 2px 6px;
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      padding: 0 8px;
      line-height: 22px;

      span{
        display: inline-block;
        max-width: calc(100% - 20px);
        font-size: 12px;
        display: -webkit-box;
        -webkit-box-orient: vertical;
        -webkit-line-clamp: 1;
        overflow: hidden;
      }
      i{
        font-size: 14px;
        margin-left: 6px;
        color: #C0C4CC;
        cursor: pointer;
        &:hover{
          color: #909399;
        }
      }
    }
  }
  .floating-box{
    padding: 6px 20px 6px 10px;
    border: 1px solid #E4E7ED;
    border-radius: 4px;
    background-color: #FFF;
    box-shadow: 0 2px 12px 0 rgba(0,0,0,.1);
    z-index: 2001;
    max-height: 800px;
    max-width: 1000px;
    overflow-y: auto;
    overflow-x: auto;
    position: absolute;
  }
}