//自定義指令：實(shí)現(xiàn)下拉框下拉到末尾時(shí)，加載下一頁(yè)的內(nèi)容
// 使用時(shí)傳兩個(gè)參數(shù)，一個(gè)是下拉框的class，一個(gè)是下拉框滾動(dòng)到末尾時(shí)觸發(fā)的函數(shù)，比如：
// v-el-select-loadmore="{
//   selector: '.myOption .el-select-dropdown .el-select-dropdown__wrap',
//   loadFunction: loadMore
// }"
export default {
  mounted(el, binding) {
    //解構(gòu)傳來(lái)的值
    const {
      value: { selector, loadFunction }
    } = binding
    const SELECTWRAP_DOM = document.querySelector(selector)
    if (SELECTWRAP_DOM) {
      // 監(jiān)聽事件的處理函數(shù)，把函數(shù)單獨(dú)寫出來(lái)，方便銷毀
      const scrollHandler = () => {
        const condition = SELECTWRAP_DOM.scrollTop + SELECTWRAP_DOM.clientHeight >= SELECTWRAP_DOM.scrollHeight - 1
        if (condition) {
          loadFunction()
        }
      }
      //賦值，為了方便銷毀，這里很重要，不然銷毀的時(shí)候找不到dom和對(duì)應(yīng)的回調(diào)函數(shù)?。?！
      el.dom = SELECTWRAP_DOM
      el.event = scrollHandler
      //監(jiān)聽滾動(dòng)事件
      SELECTWRAP_DOM.addEventListener('scroll', scrollHandler)
    }
  },
//銷毀，會(huì)在關(guān)閉彈窗時(shí)觸發(fā)（這里的el-select寫在彈窗里）
  beforeUnmount(el) {
    if (el.dom) {
      el.dom.removeEventListener('scroll', el.event)
    }
  }
}

import vElSelectLoadmore from '@/utils/tools/selectLoadMore'
app.directive('el-select-loadmore', vElSelectLoadmore) //全局自定義指令
app.mount('#app')

//使用時(shí)在指令里傳值，這里有個(gè)坑！
//在el-select給一個(gè)參數(shù)popper-class="myOption"，因?yàn)閑lement-plus中ei-select的選項(xiàng)是使用的popper.js生成的，無(wú)法直接獲取，直接獲取下拉框的dom獲取不到
          <el-select
            v-el-select-loadmore="{
              selector: '.myOption .el-select-dropdown .el-select-dropdown__wrap',
              loadFunction: loadMore
            }"
            v-model="userForm.accountName"
            placeholder="請(qǐng)選擇用戶"
            popper-class="myOption"
          >
            <el-option
              v-for="(item, index) in userData"
              v-loading="optionLoading(index)"
              :key="item.id"
              :label="item.username"
              :value="item.id"
            />
          </el-select>
//總共的數(shù)據(jù)條數(shù)
let totalCount: number = 0
//當(dāng)前滾動(dòng)頁(yè)
let page: number
/**
 * 自定義指令觸發(fā)的回調(diào)
 */
function loadMore() {
  //計(jì)算總頁(yè)數(shù)
  let maxPagSize: number = Math.max(Math.ceil(totalCount / 10), 1)
  //不超過(guò)總頁(yè)數(shù)才發(fā)請(qǐng)求
  if (page < maxPagSize) {
    page += 1
    //發(fā)請(qǐng)求，獲得接口數(shù)據(jù)
    getUserListWrap(page, 10)
  }
}
/**
 * 控制下拉框loding是否出現(xiàn)，isOptionLoading是在getUserListWrap請(qǐng)求函數(shù)里面的，userData是請(qǐng)求函數(shù)獲得是下拉框數(shù)據(jù)，這樣可以使下拉到最后一個(gè)option的時(shí)候，出現(xiàn)loding效果，更加完善美觀
 * @param index 下拉框循環(huán)的index
 */
function optionLoading(index: number): boolean {
  if (isOptionLoading.value && index == userData.length - 1) {
    return true
  } else {
    return false
  }
}

export default {
  mounted(el, binding) {
    const {
      value: { selector, loadFunction }
    } = binding
    const SELECTWRAP_DOM = document.querySelector(selector)
    if (SELECTWRAP_DOM) {
      SELECTWRAP_DOM.addEventListener('scroll', function () {
        const condition = this.scrollTop + this.clientHeight >= this.scrollHeight - 1
        if (condition) {
          loadFunction()
        }
      })
    }
  }
}

<template>
  <el-form-item label="用戶名稱：">
        <el-select 
        popper-class="myOption"
          v-model="accountName" 
          placeholder="請(qǐng)輸入或選擇用戶"  
           v-el-select-loadmore="loadMore">
            <el-option v-for="item in options" 
            :key="item.value" 
            :label="item.label" 
            :value="item.value" />
        </el-select>
        </el-form-item>
</template>
<script setup lang="ts">
import {ref,onMounted} from 'vue'
let page = ref(1)
let pageSize = ref(10)
let total = 100
let totalCount=6
let stopLoading = false
let accountName = ref('')
const options = ref([])
onMounted(() => {
  options.value.length=0
  loadOptions(1)
})
function loadMore() {
  //這里設(shè)置接口的最大頁(yè)數(shù)totalCount為6，超過(guò)6頁(yè)就沒(méi)數(shù)據(jù)了
        if (page.value <= totalCount) {
            page.value += 1;
        //獲得接口數(shù)據(jù)
          loadOptions(page.value);
        }
    }
function loadOptions(page:number) {
      // 模擬接口發(fā)送數(shù)據(jù)，異步加載數(shù)據(jù)
      setTimeout(() => {
        for (let i = (page-1)*10+1; i <= page*10; i++) {
        options.value.push({
        value: `Option${i}`,
        label: `Option${i}`
        });
        }
      }, 500);
}
//在自定義指令
const vElSelectLoadmore = {
  mounted(el: any, binding: any) {
    // 坑：
    const SELECTWRAP_DOM:Element|null = document.querySelector(
                '.myOption .el-select-dropdown .el-select-dropdown__wrap'
    );
    if (SELECTWRAP_DOM) {
      SELECTWRAP_DOM.addEventListener('scroll', function () {
                const condition = this.scrollTop+this.clientHeight >= this.scrollHeight-1;
        // 當(dāng)滾動(dòng)條滾動(dòng)到最底下的時(shí)候執(zhí)行接口加載下一頁(yè)
        if (condition) {
          binding.value && binding.value()
        }
            });
    }
  },
}
</script>