vxe-list vue 如何實現下拉框的虛擬列表

<div class="my-select">
   <input type="text" class="my-select-input" readonly>
    <vxe-list class="my-select-wrapper" :loading="loading" :data="list">
        <template v-slot="{ items }">
            <div class="my-select-option" v-for="item in items" :key="item.value">{{ item.label }}</div>
        </template>
    </vxe-list>
</div>

export default {
	data () {
		return {
	      loading: false,
	      list: []
	    }
	},
	created () {
	    this.loading = true
        setTimeout(() => {
            const startTime = Date.now()
            var list = []
            for(var i=0;i<100000;i++){
                list.push({
                    label: '選項'+i,
                    value: i
                })
            }
            this.list = list
            this.loading = false
            this.$nextTick(() => {
                this.$XModal.message({ message: `渲染 ${list.length} 行，用時 ${Date.now() - startTime}毫秒`, status: 'info' })
            })
        }, 200)
	}
}

.my-select {
    width: 200px;
    position: relative;
    background-color: #fff;
}
.my-select-input {
    width: 100%;
    height: 24px;
    border: 1px solid #dcdfe6;
}
.my-select-wrapper {
    position: absolute;
    left: 0;
    top: 26px;
    width: 100%;
    height: 200px;
    background-color: #fff;
    border: 1px solid #dcdfe6;
}
.my-select-option:hover {
    background-color: #f5f7fa;
    cursor: pointer;
}

<template>
     <div 
    class="list-view"
    :style="{
        height: `${height}px`
    }" 
    @scroll="handleScroll">
        <div
        class="list-view-phantom"       
        :style="{
            height: contentHeight
        }">
        </div>
        <ul
        ref="content"
        class="list-view-content">
            <li
                class="list-view-item"
                :style="{
                    height: itemHeight + 'px'
                }"
                v-for="(item, index) in visibleData" 
                :key="index">
                    {{ item }}
            </li>
        </ul>
  </div>
</template>

<script>
export default {
    name: 'ListView',
    props: {
    data: {
        type: Array,
        default: function() {
            const list = []
            for (let i = 0; i < 1000000; i++) {
                list.push('列表' + i)
            }
            return list
        }
    },
    height: {
        type: Number,
        default: 400
    },
    itemHeight: {
        type: Number,
        default: 30
    },
  },
  computed: {
    contentHeight() {
        return this.data.length * this.itemHeight + 'px';
    }
  },
  mounted() {
      this.updateVisibleData();
  },
  data() {
    return {
      visibleData: []
    };
  },
  methods: {
    updateVisibleData(scrollTop) {
        scrollTop = scrollTop || 0;
        const visibleCount = Math.ceil(this.$el.clientHeight / this.itemHeight); // 取得可見區域的可見列表項數量
        const start = Math.floor(scrollTop / this.itemHeight); // 取得可見區域的起始資料索引
        const end = start + visibleCount; // 取得可見區域的結束資料索引
        this.visibleData = this.data.slice(start, end); // 計算出可見區域對應的資料，讓 Vue.js 更新
        this.$refs.content.style.webkitTransform = `translate3d(0, ${ start * this.itemHeight }px, 0)`; // 把可見區域的 top 設定為起始元素在整個列表中的位置（使用 transform 是為了更好的效能）
    },
    handleScroll() {
        const scrollTop = this.$el.scrollTop;
        this.updateVisibleData(scrollTop);
    }
  }
}
</script>

<style lang="scss" scoped>
.list-view {
    overflow: auto;
    position: relative;
    border: 1px solid #aaa;
    width: 200px;
}
.list-view-phantom {
    position: absolute;
    left: 0;
    top: 0;
    right: 0;
    z-index: -1;
}
.list-view-content {
    left: 0;
    right: 0;
    top: 0;
    position: absolute;
}
.list-view-item {
    padding: 5px;
    color: #666;
    line-height: 30px;
    box-sizing: border-box;
}
</style>