微信小程序 懒加载

今天给大家带来小程序懒加载的办法，来提高页面的体验性。

理念：加入滚动，当页面滚动的时候计算列表数据的高度来判断该区域数据图片是否加载显示

1.首先我们要在wxml要显示的列表里加入滚动条

<scroll-view  bindscroll="scroll" style="height:{{clientHeight}}px;" scroll-y="true"></scroll-view>

然后。。。

wxml:

<view class="row"><scroll-view  bindscroll="scroll" style="height:{{clientHeight}}px;" scroll-y="true"><swiper indicator-dots="{{indicatorDots}}"  autoplay="{{autoplay}}" interval="{{interval}}" duration="{{duration}}" class="newCourse_bann">  <block wx:for="{{imgUrls}}">    <swiper-item>      <image src="{{item}}" class="newCourse_bann_img"/>    </swiper-item>  </block></swiper>  <form bindsubmit="formSubmit" bindreset="formReset"><input type="text" class="search" name='search' placeholder="请输入关键字..."  placeholder-style="color:#979797"/><button formType="submit" class="search_sub">搜索</button>  </form><view class="mu_item_title"><view class="item_title_line"></view><view class="item_title_ctn"><view class="item_title_ctn_center"><image src="/we7_wxappdemo/resource/images/fire.png" alt="" class="mu_item_title_img"></image><text class="mu_item_title_txt">店铺推荐</text></view></view></view><view class="list_flex"><view class="list_flex_son" wx:for="{{list}}"><navigator url="../detail/detail?id={{item.id}}" hover-class="navigator-hover"><image class="list_flex_son_img product_image {{arr[index]? 'loaded':''}}" src="https://wechat.ixunluo.com/weishopcs/attachment/{{arr[index]?item.thumb:'images/default.jpg'}}"></image><view class="list_flex_son_title">{{item.title}}</view></navigator><view class="list_flex_son_row"><text class="sfsr_price">￥{{item.marketprice}}</text><text class="sfsr_tbprice">淘宝价：{{item.productprice}}元</text></view></view></view><!-- footer end--></scroll-view></view>

核心js代码：

//计算窗口高度    wx.getSystemInfo({      success: function(res) {        self.setData({          clientHeight: res.windowHeight        });      }    })

//高度算法 var arr = [];          var length = Array.from(res.data.data).length;          var isD = length % 2 == 0 ? true : false ;          var arrHight = [];          for(var i = 0; i < length ; i++){            arr[i] = false;            arrHight[i] = Math.floor(i/2)*(320/750)*520;

for (var i = 0; i < this.data.list.length; i++) {      if (arrHight[i] < scrollTop) {          if (arr[i] == false) {              arr[i] = true;          }      }    }

scroll: function(e){      var seeHeight = this.data.clientHeight; //可见区域高度      var arrHight = this.data.arrHight;      var event = e;      var scrollTop = event.detail.scrollTop;      var arr = this.data.arr;      // console.log(scrollTop)      for (var i = 0; i < this.data.list.length; i++) {          if (arrHight[i] < scrollTop) {              if (arr[i] == false) {                  arr[i] = true;                  // arr[i*2]   arr[i*2+1]               }              //n = i + 1;          }          //arr[i] = true;      }      this.setData({          arr : arr      })  }

完整js：

var app = getApp();Page({  data: {    GZtate: true,    // 轮播    imgUrls: [      '/we7_wxappdemo/resource/images/lunbo1.jpg',      '/we7_wxappdemo/resource/images/lunbo2.jpg',      '/we7_wxappdemo/resource/images/lunbo3.jpg'    ],    indicatorDots: false,    interval: 5000,    duration: 1000,    autoplay: true,    // over    list:[],  clientHeight:0, arr:[], arrHight:[] },onLoad: function (options) {    // 页面初始化 options为页面跳转所带来的参数    const self = this;    wx.getSystemInfo({      success: function (res) {        self.setData({          clientHeight: res.windowHeight        });      }    })    // console.log(options)    var tarrHight = [];    app.util.request({      'url': 'entry/wxapp/list',      data: {        category: options.category ? options.category : '',      },      'cachetime': '30',      success(res) {        //console.log(res);        self.setData({          list: res.data.data        })        //         var arr = [];        var length = Array.from(res.data.data).length;        var isD = length % 2 == 0 ? true : false;                for (var i = 0; i < length; i++) {          arr[i] = false;          tarrHight[i] = Math.floor(i / 2) * (320 / 750) * 520;        }        self.setData({          arr: arr,          list: Array.from(res.data.data),          arrHight: tarrHight        })        //  console.log(self.data.arr)        //       },    })    for (var i = 0; i < self.data.list.length; i++) {      if (tarrHight[i] < self.data.scrollTop) {        if (arr[i] == false) {          arr[i] = true;        }      }    }    // 上拉加载    //点击搜索按钮，触发事件     self.setData({      listPageNum: 1, //第一次加载，设置1       List: [], //放置返回数据的数组,设为空       isFromlist: true, //第一次加载，设置true       listLoading: true, //把"上拉加载"的变量设为true，显示       listLoadingComplete: false //把“没有数据”设为false，隐藏     })    self.fetchlist();  },scroll: function (e) {    //console.log(this.data);    var seeHeight = this.data.clientHeight; //可见区域高度    var arrHight = this.data.arrHight;    var event = e;    var scrollTop = event.detail.scrollTop;    var arr = this.data.arr;    // console.log(scrollTop)    for (var i = 0; i < this.data.list.length; i++) {      if (arrHight[i] < scrollTop) {        if (arr[i] == false) {          arr[i] = true;          // arr[i*2]   arr[i*2+1]         }        //n = i + 1;      }      //arr[i] = true;    }    this.setData({      arr: arr,      scrollTop:scrollTop    })  },

效果图：