老师，我这里为什么打印this.$refs[this.letter]是undefined

Question

<template>
  <div class='list' ref='wrapper'>
    <div>
      <div class='area'>
        <div class='title border-topbottom'>当前城市</div>
        <div class="button-list">
          <div class="button-wrapper">
            <div class='button'> 北京</div>
          </div>
        </div>
      </div>
      <div class='area'>
       <div class='title border-topbottom'>热门城市</div>
        <div class="button-list">
          <div class="button-wrapper" v-for='item of hot' :key='item.id'>
            <div class='button'> {{item.name}} </div>
          </div>
        </div>
    </div>
    <div class='area' v-for='(item,key) of cities' :key='key' :ref='key'>
      <div class='title border-topbottom'>{{key}}</div>
      <div class="item-list">
        <div class='item border-bottom' v-for='innerItem of item' :key='innerItem.id'>
          {{innerItem.name}}
        </div>
      </div>
      </div>
    </div>
  </div>
</template>

<script>
import Bscroll from 'better-scroll'
export default {
  name: 'List',
  props: {
    hot: Array,
    cities: Object,
    letter: String
  },
  watch: {
    letter () {
      if (this.letter) {
        const element = this.$refs[this.letter]
        // undefined  why?
        console.log(element)
        // 点击字母列表能打印出对应的字母
        console.log(this.letter)
      }
    }
  },
  mounted () {
    this.scroll = new Bscroll(this.$refs.wrapper)
  }
}
</script>

<style lang='stylus' scoped>
  @import '~styles/varibles.styl'
  .border-topbottom
    &:before
      border-color: #777
    &:after
      border-color: #777
  .border-bottom
    &:before
      border-color: #000
  .list
    overflow: hidden
    position: absolute
    top: 1.58rem
    right: 0
    left: 0
    bottom: 0
    .title
      line-height: .54rem
      background: #eee
      padding-left: .2rem
      color: #666
      font-size: .26rem
    .button-list
      overflow: hidden
      padding: .1rem .6rem .1rem .1rem
      .button-wrapper
        float: left
        width: 33.33%
        .button
          margin: .1rem
          padding: .1rem 0
          text-align: center
          border: .02rem solid #ccc
          border-radius: .06rem
    .item-list
      .item
        line-height: .62rem
        padding-left: .2rem
</style>

Answer 1

hei客 2019-07-12 10:51:14

我也是

Answer 2

Dell 2019-06-05 14:49:25

分别打印 this.$refs 和 this.letter， 看一下哪一个东西有问题。

• 小芙a #1

  老师，我打印this.$refs能打印出来对象，this.letter能打印出来字母，但是this.$refs[this.letter]就变成undefined，是怎么回事啊？

• Dell 回复 小芙a #2

  一开始没有渲染的时候，有可能是undefined，所以建议做个判断，如果存在再做下一步操作