实现功能

点击左侧,右侧滚动到相应位置,
滚动右侧, 左侧滚动到相应位置

布局结构

开源滚动库

better-scroll.js

技术要点

1.<scroll>是对紧邻的元素生效
如:

<scroll class='foods-wrapper'>
    <ul class=content>
      <li></li>
    </ul>
  </scroll>

初始化在<ul>元素上

2.foods-wrapper的高度小于content高度时才会发生滚动

3.点击左侧菜单列表时,只需要计算右侧对应的偏移距离 或是 计算对应的移动到的元素即可
方法一: 计算移动距离, 用scrollTo()方法

  for (let i = 0; i < index; i++) {
    height += this.$refs.item[i].offsetHeight
  }
  this.$refs.foodsWrapper.scrollTo(0, -height)
  

方法二: 计算移动到的元素,用scrollToElement()方法

  let foodsEle = this.$refs.foodsUl.getElementsByClassName('item')[index]
  this.$refs.foodsWrapper.scrollToElement(foodsEle, 400)

4.滚动右侧列表时,会稍复杂一些.

4.1. 因为需要知道滚动的元素在哪个item列表区间, 因此需要计算右侧五组item距离顶部的距离

_heightArr () {
  let h = 0
  let list = this.$refs.item
  list.forEach((item, i) => {
    h += list[i].clientHeight
    this.itemHeight.push(h)
  })
   console.log(this.itemHeight)  //[0, 481, 850, 2227, 2820, 3189]
}

4.2 时时监听滚动距离

需要在<scroll>中加以下参数
<scroll class='foods-wrapper' :listenScroll=listenScroll :probeType = 'probeType' @scroll=scroll>
其中 listenScroll probeType参数 在created中定义:

  created () {
    this.listenScroll = true
    this.probeType = 3
  }

而@scroll=scroll是在scroll.vue中代理过来的方法:

  //scroll.vue
  if (this.listenScroll) {
    let me = this
    this.scroll.on('scroll', (position) => {
      me.$emit('scroll', position) //参数position:  position:{x:-10, y:24}
    })
  }

posiiton.y就是需要实时监听的参数,即:

scroll (position) {
  this.scrolly = position.y
}

其中 scrolly 需要在data中提前定义:

  data () {
    return {
      scrolly: -1
    }
  }

然后在watch中监听scrolly变化即可:

  watch: {
    scrolly (newy) {
      if (newy >= 0) this.currentIndex = 0
      let itemHeight = this.itemHeight
      for (let i = 0; i < itemHeight.length - 1; i++) {
        let h1 = itemHeight[i]
        let h2 = itemHeight[i + 1]
        if (-newy >= h1 && -newy < h2) {
          this.currentIndex = i
          return
        }
      }
    }
  }

附:代码部分

//左侧结构
  <scroll class='menu-wrapper'>
    <ul>
      <li 
        v-for='(item,index) in foodsList' 
        :key=index 
         class=item 
        :class="{active:currentIndex === index}" 
        @click=selectMenu(index)
      >
        <span>{{item.name}}</span>
      </li>
    </ul>
  </scroll>


//右侧结构
  <scroll class='foods-wrapper' ref=foodsWrapper :listenScroll=listenScroll  :probeType = 'probeType' @scroll=scroll>
    <ul ref=foodsUl> 
      <li v-for='(item,index) in foodsList' :key=index class=item ref=item :data-index=index>
        <div class=title><span class='title-name'>{{item.name}}</span><span>{{item.description}}</span></div>
        <ul>
          <li v-for='(food,i) in item.foods' :key=i class=food>
          //.........
          //略去右侧详情代码
          </li>
        </ul>
      </li>
    </ul>
  </scroll>

//js部分
<script>
import Scroll from "base/scroll"
const H = 112
export default {
  data () {
    return {
      currentIndex: 0,
      offset: 0,
      scrolly: -1
    }
  },
  created () {
    this.listenScroll = true
    this.probeType = 3
    this.itemHeight = [0]
  },
  mounted () {
    this.$nextTick(() => {
      this._heightArr()
    }, 20);
  },
  methods: {
    selectMenu (index) {
      let height = 0
      this.currentIndex = index

      for (let i = 0; i < index; i++) {
        height += this.$refs.item[i].offsetHeight
      }

      let foodsEle = this.$refs.foodsUl.getElementsByClassName('item')[index]
      this.$refs.foodsWrapper.scrollToElement(foodsEle, 400)
      // this.$refs.foodsWrapper.scrollTo(0, -height)
      this.offset = height
    },
    scroll (position) {
      this.scrolly = position.y
    },
    _heightArr () {
      let h = 0
      let list = this.$refs.item
      list.forEach((item, i) => {
        h += list[i].clientHeight
        this.itemHeight.push(h)
      })
    }
  },
  watch: {
    scrolly (newy) {
      if (newy >= 0) this.currentIndex = 0
      let itemHeight = this.itemHeight
      for (let i = 0; i < itemHeight.length - 1; i++) {
        let h1 = itemHeight[i]
        let h2 = itemHeight[i + 1]
        if (-newy >= h1 && -newy < h2) {
          this.currentIndex = i
          return
        }
      }
    }

  },
  components: {
    Scroll
  }


}
</script>

//scroll.vue
<template>
  <div ref=wrapper>
    <slot></slot>  
  </div>
</template>

<script>
import BScroll from 'better-scroll'
export default {
  props: {
    probeType: {
      type: Number,
      default: 1//* 1 滚动的时候会派发scroll事件，会截流。 * 2 滚动的时候实时派发scroll事件，不会截流。 * 3 除了实时派发scroll事件，在swipe的情况下仍然能实时派发scroll事件
    },
    click: {
      type: Boolean,
      default: true
    },
    scrollX: {
      type: Boolean,
      default: false
    },
    data: {
      type: Array,
      default: null
    },
    listenScroll: {
      type: Boolean,
      default: false
    },

  },
  mounted () {
    this.$nextTick(() => {
      this.initScroll()
    }, 20)
  },
  methods: {
    initScroll () {
      if (!this.$refs.wrapper) return
      this.scroll = new BScroll(this.$refs.wrapper, {
        probeType: this.probeType,
        click: this.click,
        scrollX: this.scrollX
      })

      if (this.listenScroll) {
        let me = this
        this.scroll.on('scroll', (position) => {
          me.$emit('scroll', position)

        })
      }
    },
    enable () {
      this.scroll && this.scroll.enable()
    },
    disable () {
      this.scroll && this.scroll.disable()
    },
    refresh () {
      this.scroll && this.scroll.refresh()
    },
    scrollTo () {
      this.scroll && this.scroll.scrollTo.apply(this.scroll, arguments)
    },

    scrollToElement () {
      this.scroll && this.scroll.scrollToElement.apply(this.scroll, arguments)
    }

  },
  watch: {
    data () {
      setTimeout(() => {
        this.scroll.refresh()
      }, 20)
    }
  }

}
</script>