<template>
  <div id="app">
    <van-picker show-toolbar title="標(biāo)題" :columns="columns" @change="checkScroll" />
  </div>
</template>
<script>
export default {
  name: 'App',
  data () {
    return {
      columns: [{
        text: '浙江',
        children: [{
          text: '溫州溫州溫州溫州溫州溫州溫州-杭州',
          children: [{ text: '西湖區(qū)' }, { text: '余杭區(qū)' }],
        }, {
          text: '溫州溫州溫州溫州溫州溫州溫州-溫州',
          children: [{ text: '鹿城區(qū)' }, { text: '甌海區(qū)' }],
        }]
      }]
    }
  },
  methods: {
    checkScroll () {
      this.$nextTick(() => {
        // 獲取選中元素
        let selectedItems = [...document.querySelectorAll('.van-picker-column__item--selected')]
        selectedItems.forEach(item => {
          let child = item.querySelector('.van-ellipsis')
          if (child.offsetWidth > item.offsetWidth) { // 判斷child文字寬度
            item.classList.add('scroll')
          } else {
            item.classList.remove('scroll')
          }
        })
      })
    }
  }
}
</script>

<style lang="less" scoped>
/deep/ .van-picker-column__item--selected {
  /* 重寫選中后的效果 */
  .van-ellipsis {
    text-overflow: unset;
    overflow: visible;
  }
  /* 增加scroll類 */
  &.scroll > .van-ellipsis {
    animation: move 4s linear infinite;
  }
}
@keyframes move {
  0% { transform: translateX(100%); }
  100% { transform: translateX(-100%); }
}
</style>

<van-field
  readonly
  clickable
  label="城市"
  :value="value"
  placeholder="選擇城市"
  @click="showPicker = true"
/>
<van-popup v-model="showPicker" round position="bottom">
  <van-picker
    show-toolbar
    :columns="columns"
    value-key="name" 
    @cancel="showPicker = false"
    @confirm="onConfirm"
  />
</van-popup>
<!--
重點(diǎn)：自定義value-key屬性：默認(rèn)值是text
value-key這個(gè)屬性是自定義后臺(tái)返回字段作為選擇器顯示的內(nèi)容，這樣后臺(tái)返回的字段位未name時(shí)，也可以顯示了。
否則默認(rèn)的原始對(duì)象默認(rèn)是[{text:'選項(xiàng)一',value:'1'},{text:'選項(xiàng)二',value:'2'}]
-->