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小程序-云开发 bindscroll滚动事件执行setData()方法,导致scroll-view视图抖动

风随心动* 人气:3

需求描述

想做一个类似京东小程序首页功能列表左右滑动的效果,效果图如下

 

遇到的问题

1. 如何让scroll-view显示两行

做过小程序开发的都知道,scroll-view要么显示一行,可以左右滚动,如果显示两行的话就会适应屏幕宽度,达不到左右滚动的效果,所以我们需要改变一下我们的数据结构


        [{
          item: [{
            "_id": "2",
            "id": 7,
            "name": "javaScript",
            "style": "#fef2ce",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/java-script.png?sign=bc895f0a0344a1415b9b829713bf111c&t=1563077572"
          }, {
            "_id": "3",
            "id": 2,
            "name": "vue",
            "style": "#EB7347",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/Vue.png?sign=37ba4970e938cb3419b3209d572a8013&t=1563077541"
          }]
        }, {
          item: [{
            "_id": "4",
            "id": 1,
            "name": "小程序",
            "style": "#fc9",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/%E5%B0%8F%E7%A8%8B%E5%BA%8F.png?sign=1513baa85fdce9f0f5ee0a2d496c1613&t=1563077605"
          }, {
            "_id": "5",
            "id": 4,
            "name": "浏览器",
            "style": "#00CCFF",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/%E6%B5%8F%E8%A7%88%E5%99%A8.png?sign=a315bc182fc89b7adb65a07c4da96eac&t=1565352298"
          }]
        }, {
          item: [{
            "_id": "6",
            "id": 5,
            "name": "android",
            "style": "#AEDD81",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/Android.png?sign=3411681e3b4d3eba93566a19f8c5a297&t=1563077457"
          }, {
            "_id": "7",
            "id": 3,
            "name": "react",
            "style": "#13227a",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/React.png?sign=b6466f2dbea9d0d83da78e0fa04e3b40&t=1563077529"
          }]
        }, {
          item: [{
            "_id": "8",
            "id": 8,
            "name": "css3",
            "style": "#e1d7f0",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/CSS.png?sign=4661566c2350d00d3cd1ddd66967f96a&t=1563077493"
          }, {
            "_id": "9",
            "id": 6,
            "name": "nodeJS",
            "style": "#fadbd9",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/Nodejs.png?sign=084f064382cdd700c5586a7e6ea65f30&t=1563077507"
          }]
        }, {
          item: [{
            "_id": "10",
            "id": 9,
            "name": "html5",
            "style": "#D24D57",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/html5.png?sign=65a8c526612ceb1edc217767c3e19a2f&t=1563077559"
          }, {
            "_id": "1",
            "id": 10,
            "name": "旅拍",
            "style": "#e8f4d9",
            "url": "https://6366-cfxy-mall-pxwnv-1256640731.tcb.qcloud.la/classfication_images/%E6%97%85%E6%8B%8D%E7%85%A7.png?sign=3b3311d664f368e6525a7fb5e13d76b1&t=1565856664"
          }]
        }]

我们再来看看wxml如何渲染这些数据

<scroll-view class="classfication-scroll" scroll-with-animation='true' scroll-anchoring='true' scroll-x enable-flex bindscroll='bindscroll'>
 <view class="scroll-view-item">
    <view wx:for="{{classficationList}}" class="child">
       <view class='classfication-view' wx:for="{{item.item}}" wx:for-item='child' wx:key="_id" wx:if="{{child._id<50}}" data-id='{{child.id}}' data-name='{{child.name}}' bindtap='click'>
          <view class='image' style='background:{{child.style}}'>
                <image src="{{child.url}}" />
            </view>
             <view class='name'>{{child.name}}</view>
          </view>
    </view>
  </view>
</scroll-view>

 

2. 如何让底部的scroll-bar跟随着上面的功能列表进行滑动

首先需要获取scroll-view滑动的距离,这里用到scroll-view的bindscroll='bindscroll'方法,


  bindscroll(event) {
    const {scrollLeft,scrollWidth} = event.detail;
    var sc = this.data.scrollWidth; // 屏幕宽度
    var canScroll = scrollWidth - sc; // 能滚动的宽度
    var move = scrollLeft / canScroll / 2 * 100;
    this.setData({
      scrollBar: move
    })
  }

关键代码:

var move = scrollLeft / canScroll / 2 * 100;

3. 如何解决左右滑动视图抖动的问题

解决方案:当滑动到最左或者左右的时候直接return,不执行setData方式,减少性能消耗

  bindscroll(event) {
    const {
      scrollLeft,
      scrollWidth
    } = event.detail;
    if (scrollLeft < 0) { // 向右滑动时超出屏幕就return
      return
    }
    var sc = this.data.scrollWidth; // 屏幕宽度
    var canScroll = scrollWidth - sc; // 能滚动的宽度
    if (scrollLeft > canScroll) { // 向左滑动时超出屏幕就return
      return
    }
    var move = scrollLeft / canScroll / 2 * 100;
    this.setData({
        scrollBar: move
      })
  },

 

4. 使用防抖的思想再次优化快速滑动时的性能消耗

  bindscroll(event) {
    const {
      scrollLeft,
      scrollWidth
    } = event.detail;
    if (scrollLeft < 0) { // 向右滑动时超出屏幕就return
      return
    }
    var sc = this.data.scrollWidth; // 屏幕宽度
    var canScroll = scrollWidth - sc; // 能滚动的宽度
    if (scrollLeft > canScroll) { // 向左滑动时超出屏幕就return
      return
    }
    var timer = null;
    var _this = this
    timer = setTimeout(() => {
      clearTimeout(timer)
      var move = scrollLeft / canScroll / 2 * 100;
      _this.setData({
        scrollBar: move
      })
    }, 300);
  },

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