当better-scroll遇上vue,不一样的坑

前言

不久前，遇到这样的一个APP需求，头部一个tab,下面是一个列表，要实现上拉加载更多，下拉刷新。在度娘里找到了better-scroll，参照better-scroll的demo,实现了一个scroll组件

scroll组件

html

 <div class="mux-scroll-wrapper" :style="scrollStyle">
<div class="mux-scroll-container">
  <slot></slot>
  <slot name="pullup" :is-pullup="isPullup" :is-no-more="isNoMore" :is-pullup-loading="isPullupLoading">
    <div class="mux-pullup-container" v-if="isPullup">
      <div class="mux-pullup-nodata" v-if="isNoMore">
        <span>{{noMoreTxt}}</span>
      </div>
      <div class="mux-pullup-more" v-else>
        <div class="mux-pullup-loading" v-if="isPullupLoading">
          <inline-loading></inline-loading>
        </div>
        <div class="mux-pullup-tips" v-else>
          <span>{{pullupTxt}}</span>
        </div>
      </div>
    </div>
  </slot>
</div>
<slot name="pulldown" :is-pulldowm="isPulldown" :pulldown-style="pulldownStyle" :is-prior-pulldown="isPriorPulldown" :is-pulldown-loading="isPulldownLoading" :dir-y="dirY">
  <div class="mux-pulldown-container" :style="pulldownStyle" v-if="isPulldown">
    <div class="mux-before-pulldown" v-if="isPriorPulldown">
      <spinner :y="dirY"></spinner>
    </div>
    <div class="mux-after-pulldown" v-else>
      <div class="mux-pulldown-loading" v-if="isPulldownLoading">
        <inline-loading></inline-loading>
      </div>
      <div class="mux-pulldown-fresh" v-else>{{pulldowmTxt}}</div>
    </div>
  </div>
</slot>
</div>

import BScroll from 'better-scroll'
import Spinner from '@/components/spinner'
import InlineLoading from '@/components/inline-loading'
export default {
  props: {
    value: {
      type: Boolean,
      default: false
    },
    interval: {
      type: Number,
      default: 0
    },
    isNoMore: {
      type: Boolean,
      default: false
    },
    probeType: {
      type: Number,
      default: 2
    },
    lockClick: {
      type: Boolean,
      default: true
    },
    lockScroll: {
      type: Boolean,
      default: false
    },
    lockBeforeScroll: {
      type: Boolean,
      default: false
    },
    lockScrollEnd: {
      type: Boolean,
      default: false
    },
    direction: {
      type: String,
      default: 'vertical',
      validator (v) {
        return ['vertical', 'horizontal'].indexOf(v) > -1
      }
    },
    scrollbar: {
      type: [Object, Boolean],
      default: false
    },
    pullDownRefresh: {
      type: [Object, Boolean],
      default: false
    },
    pullUpLoad: {
      type: [Object, Boolean],
      default: false
    },
    startY: {
      type: Number,
      default: 0
    },
    refreshDelay: {
      type: Number,
      default: 20
    },
    freeScroll: {
      type: Boolean,
      default: false
    },
    mouseWheel: {
      type: Boolean,
      default: false
    },
    bounce: {
      default: true
    },
    zoom: {
      default: false
    }
  },
  components: {
    InlineLoading,
    Spinner
  },
  data () {
    return {
      isPullup: false,
      isPulldown: false,
      isPriorPulldown: false,
      isFinishPulldown: false,
      isPulldownLoading: false,
      isPulldownRefresh: false,
      isPulldownRebound: false,
      isPullupMore: false,
      isPullupLoading: false,
      isFinishPullup: false,
      pulldownStyle: { top: '-56px' },
      dirY: 0,
      initThreshold: -56,
      scroll: null
    }
  },
  computed: {
    pullupTxt () {
      return (this.pullUpLoad && this.pullUpLoad.moreTxt) || '上拉加载更多'
    },
    noMoreTxt () {
      return (this.pullUpLoad && this.pullUpLoad.noMoreTxt) || '没有更多数据'
    },
    pulldowmTxt () {
      return (this.pullDownRefresh && this.pullDownRefresh.txt) || '刷新成功'
    },
    scrollStyle () {
      let maxheight = document.documentElement.clientHeight || document.body.clientHeight
      return { height: (maxheight - this.interval) + 'px' }
    }
  },
  watch: {
    value (nv, ov) {
      if (nv === ov) { return }
      this.fetchCompleted(nv)
    },
    isFinishPulldown (nv, ov) {
      if (nv === ov) { return }
      this.pulldownUpdate(nv)
    },
    isFinishPullup (nv, ov) {
      if (nv === ov) { return }
      this.pullupUpdate(nv)
    }
  },
  mounted () {
    this.$nextTick(() => {
      if (!this.scroll) {
        this.initScroll()
      }
    })
  },
  destroyed () {
    this.scroll && this.scroll.destroy()
  },
  methods: {
    initScroll () {
      let options = {
        probeType: this.probeType,
        click: this.lockClick,
        scrollY: this.freeScroll || this.direction === 'vertical',
        scrollX: this.freeScroll || this.direction === 'horizontal',
        scrollbar: this.scrollbar,
        pullDownRefresh: this.pullDownRefresh,
        pullUpLoad: this.pullUpLoad,
        startY: this.startY,
        freeScroll: this.freeScroll,
        mouseWheel: this.mouseWheel,
        bounce: this.bounce,
        zoom: this.zoom
      }
      this.scroll = new BScroll(this.$el, options)
      if (this.lockScroll) {
        this.scroll.on('scroll', (pos) => {
          this.$emit('scroll', pos)
        })
      }
      if (this.lockScrollEnd) {
        this.scroll.on('scrollEnd', (pos) => {
          this.$emit('scroll-end', pos)
        })
      }
      if (this.lockBeforeScroll) {
        this.scroll.on('beforeScrollStart', () => {
          this.$emit('before-scroll-start')
        })
        this.scroll.on('scrollStart', () => {
          this.$emit('scroll-start')
        })
      }
      if (this.pullDownRefresh) {
        this.isPulldown = true
        this.initPullDown()
      }
      if (this.pullUpLoad) {
        this.isPullup = true
        this.initPullUp()
      }
    },
    initPullDown () {
      this.scroll.on('scrollStart', () => {
        this.isPriorPulldown = true
      })
      this.scroll.on('pullingDown', () => {
        this.isPriorPulldown = false
        this.isPulldownRefresh = true
        this.isPulldownLoading = true
        this.$emit('pulling-down')
      })
      this.scroll.on('scroll', (pos) => {
        if (!this.pullDownRefresh) {
          return
        }
        if (this.isPriorPulldown) {
          this.dirY = Math.max(0, pos.y + this.initThreshold)
          this.pulldownStyle = `top:${Math.min(pos.y + this.initThreshold, 10)}px`
        } else {
          this.dirY = 0
        }
        if (this.isPulldownRebound) {
          this.pulldownStyle = `top:${10 - (this.pullDownRefresh.stop - pos.y)}px`
        }
      })
    },
    initPullUp () {
      this.scroll.on('pullingUp', () => {
        if (this.isNoMore) { return }
        this.isPullupMore = true
        this.isPullupLoading = true
        this.$emit('pulling-up')
      })
    },
    fetchCompleted (isComplete) {
      if (isComplete) {
        if (this.isPulldownRefresh) {
          this.isPulldownLoading = false
          this.isFinishPulldown = true
        }
        if (this.isPullupMore) {
          this.isPullupLoading = false
          this.isFinishPullup = true
        }
      } else {
        this.isFinishPulldown = false
        this.isFinishPullup = false
      }
    },
    pulldownUpdate (isComplete) {
      if (isComplete) {
        const { delay = 600 } = this.pullDownRefresh
        setTimeout(() => {
          this.isPulldownRebound = true
          this.scroll.finishPullDown()
          this.pulldownComplete()
        }, delay)
      } else {
        this.refresh()
      }
    },
    pulldownComplete () {
      setTimeout(() => {
        this.pulldownStyle = `top:${this.initThreshold}px`
        this.isPulldownRebound = false
        this.isPulldownRefresh = false
        this.$emit('input', false)
      }, this.scroll.options.bounceTime)
    },
    pullupUpdate (isComplete) {
      if (isComplete) {
        this.$nextTick(() => {
          this.isPullupMore = false
          this.scroll.finishPullUp()
          this.$emit('input', false)
        })
      } else {
        this.refresh()
      }
    },
    disable () {
      this.scroll && this.scroll.disable()
    },
    enable () {
      this.scroll && this.scroll.enable()
    },
    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)
    },
    destroy () {
      this.scroll.destroy()
    }
  }
}

less

        @scroll: ~"mux-scroll";
        @pullup: ~"mux-pullup";
        @pulldown: ~"mux-pulldown";
        .setClearfix() {
          position: absolute;
          display: table;
          content: "";
          box-sizing: border-box;
        }

        .@{scroll} {
          &-wrapper {
            position: relative;
            overflow: hidden;
            zoom: 1;
            height: 100%;
            transition: all .2s;
            &:before,
            &:after {
              .setClearfix()
            }
            &:after {
              clear: both;
            }
          }
          &-container {
            position: relative;
            display: block;
          }
        }

        .@{pullup} {
          &-container {
            position: relative;
            display: block;
            min-height: 40px;
            transform: translate3d(0, 0, 0) scale(1);
          }
          &-nodata {
            display: block;
            font-size: 16px;
            color: #5077aa;
            padding: 12px 0;
            text-align: center;
          }
          &-more {
            display: flex;
            justify-content: center;
            align-items: center;
            padding: 16px 0;
            width: 100%;
            margin: 0;
            padding: 0;
          }
          &-tips {
            font-size: 16px;
            color: #5077aa;
            padding: 12px 0;
            text-align: center;
          }
          &-loading {
            padding: 12px 0;
            text-align: center;
          }
        }

        .@{pulldown} {
          &-container {
            position: absolute;
            left: 0;
            width: 100%;
            display: flex;
            justify-content: center;
            align-items: center;
            transform: scale(1);
            transition: all .1s;
            & .mux-before-pulldown {
              text-align: center;
            }
            & .mux-after-pulldown {
              margin: 10px 0 0;
            }
          }
          &-loading {
            text-align: center;
          }
          &-fresh {
            font-size: 16px;
            color: #5077aa;
            text-align: center;
          }
        }

查看scrooll组件

问题

滚动元素
better-scroll创建实例：
```
 new BScroll(container, options)
```
滚动元素为container元素的第一个子元素。因此下拉刷新的提示信息必须放在滚动元素的后面。
显示不全或者不显示
容器的高度取决于网页的高度，因此webview的高度必须设置为手机屏幕的高度，否则会出现显示不全或者不现实
数据必须加载满一屏，否则无法滚动
better-scroll可是滚动的情况是它的wrapperHeight < scrollHeight，hasVerticalScroll为true；
当数据未占满一屏时：wrapperHeight >scrollHeight,因此无法滚动
数据未加载满一屏时，无法做下拉刷新
原因是不满足滚动条件，better-scroll的源码如下：
```
  if (this.directionY !== DIRECTION_DOWN || this.y < threshold) {
      return false
  }
```
因为无法滚动，y的值为0
当 tab1的数据加载完时，切换其他tab，滚动无效
better-scroll的pullingup事件在数据全部加载完时被解绑了，因此切换tab时无效。解决办法是判断数据是否加载完，如果加载完，则重新初始化pullingup事件

当better-scroll遇上vue,不一样的坑

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