AntDesingVue select下拉框中数据量过多，响应慢。使用popupScroll，下拉加载更多

在做公司的项目时，需要将行政区与区块联系下拉，导致加载的数据过多，页面响应慢，因此可以考虑使用分页的方式，用户在下拉到底部时加载更多的数据，一直到数据加载完。

ant design for vue 的select提供了popupScroll方法

具体的实现如下

<a-select
      style="width: 100%" 
      show-search
      placeholder="请选择"
      search-placeholder="请选择"
      :dropdown-style="{ maxHeight: '240px', overflow: 'auto' }"
      :value="value" 
      @change="onChange" 
      @search="searchChange"
      @popupScroll="popupScroll"
      :filter-option="false"
      not-found-content="暂无数据"
  >
      <a-select-option v-for="item in treeData" :key="item.code" :data="item" :value="item.code" :title=" item.pathName">
          {{ item.pathName}}
      </a-select-option>
  </a-select>

pageSize: 10, // 分页

pageNumber: 1,

getListDataCode(code = '') { // 获取树节点
    let self = this;
    this.$post(self.$api.getCompanyList, 
        { 
            code: code, 
            systemCode: 'SYSTEM',
            fullName:self.searchName,
            pageNumber: this.pageNumber,
            pageSize: this.pageSize,
 
        }).then((res) => {
        if(res.code - 0 === 200) {
            const resData = (res.data && res.data) || []
            this.pages= res.data.pages;
            if(this.treeData.length <= resData.total){
                this.treeData.push(...resData.records);
            }
             
             
        }
    })
},
// 文本框的值变化是
searchChange(searchValue){
    this.searchName = searchValue
    if(this.searchName){
        this.treeData = []
        this.pageNumber = 1;
        this.getListDataCode(this.parentCode)
    }
},
// 选中时调用
onChange(value,e){
    this.searchName = value;
    let data = e && e.data && e.data.attrs && e.data.attrs.data
    this.$emit('select', {...data, value, name: data.pathName})
},
popupScroll(e){
    const {target} = e;
    const scrllHeight = target.scrollHeight - target.scrollTop;
    const clientHeight = target.clientHeight;
    // 下拉框不下拉的时候
    if(scrllHeight ===0 && clientHeight ===0){
        this.pageNumber = 1;
    } else if(scrllHeight - clientHeight == 0){ // 下拉到底部时
        if(this.pageNumber < this.pages){
            // 如果滑到底部，则加载下一页
            this.pageNumber++ 
            this.getListDataCode(this.parentCode)
        }
    }
     
}