微信小程序实现页面下拉刷新和上拉加载功能详解

<!--pages/WaterFall/WaterFall.wxml-->
<view style="display:none">
 <image wx:for="{{images}}" wx:key="id" id="{{item.id}}" src="{{item.pic}}" bindload="onImageLoad"></image>
</view>
<scroll-view scroll-y="true" style="height:{{scrollH}}px" bindscrolltolower="loadImages" bindscrolltoupper="PullDownRefresh">
 <view style="width:100%">
  <view class="img_item">
   <view wx:for="{{col1}}" wx:key="id">
    <image src="{{item.pic}}" style="width:100%;height:{{item.height}}px"></image>
   </view>
  </view>
  <view class="img_item">
   <view wx:for="{{col2}}" wx:key="id">
    <image src="{{item.pic}}" style="width:100%;height:{{item.height}}px"></image>
   </view>
  </view>
 </view>
</scroll-view>

let col1H = 0;
let col2H = 0;
Page({
 data: {
  scrollH: 0,
  imgWidth: 0,
  loadingCount: 0,
  images: [],
  col1: [],
  col2: []
 },
 onLoad: function () {
  wx.getSystemInfo({
   success: (res) => {
    let ww = res.windowWidth;
    let wh = res.windowHeight;
    let imgWidth = ww * 0.48;
    let scrollH = wh;
    this.setData({
     scrollH: scrollH,
     imgWidth: imgWidth
    });
    //加载首组图片
    this.loadImages();
   }
  })
 },
 PullDownRefresh:function(){
  console.log("页面下拉2");
 },
  onShow: function () {
   console.log("页面显示");
 },
 /**
  * 生命周期函数--监听页面隐藏
  */
 onHide: function () {
  console.log("页面隐藏");
 },
 /**
  * 用户点击右上角分享
  */
 onShareAppMessage: function () {
  console.log("点击分享");
 },
 onImageLoad: function (e) {
  let imageId = e.currentTarget.id;
  let oImgW = e.detail.width;     //图片原始宽度
  let oImgH = e.detail.height;    //图片原始高度
  let imgWidth = this.data.imgWidth; //图片设置的宽度
  let scale = imgWidth / oImgW;    //比例计算
  let imgHeight = oImgH * scale;   //自适应高度
  let images = this.data.images;
  let imageObj = null;
  for (let i = 0; i < images.length; i++) {
   let img = images[i];
   if (img.id === imageId) {
    imageObj = img;
    break;
   }
  }
  imageObj.height = imgHeight;
  let loadingCount = this.data.loadingCount - 1;
  let col1 = this.data.col1;
  let col2 = this.data.col2;
  //判断当前图片添加到左列还是右列
  if (col1H <= col2H) {
   col1H += imgHeight;
   col1.push(imageObj);
  } else {
   col2H += imgHeight;
   col2.push(imageObj);
  }
  let data = {
   loadingCount: loadingCount,
   col1: col1,
   col2: col2
  };
  //当前这组图片已加载完毕，则清空图片临时加载区域的内容
  if (!loadingCount) {
   data.images = [];
  }
  this.setData(data);
 },
 loadImages: function () {
  let images = [
   { pic: "../../images/1.png", height: 0 },
   { pic: "../../images/2.png", height: 0 },
   { pic: "../../images/3.png", height: 0 },
   { pic: "../../images/4.png", height: 0 },
   { pic: "../../images/5.png", height: 0 },
   { pic: "../../images/6.png", height: 0 },
   { pic: "../../images/7.png", height: 0 },
   { pic: "../../images/8.png", height: 0 },
   { pic: "../../images/9.png", height: 0 },
   { pic: "../../images/10.png", height: 0 },
   { pic: "../../images/11.png", height: 0 },
   { pic: "../../images/12.png", height: 0 },
   { pic: "../../images/13.png", height: 0 },
   { pic: "../../images/14.png", height: 0 }
  ];
  console.log("dasddasd" + images);
  let baseId = "img-" + (+new Date());
  for (let i = 0; i < images.length; i++) {
   images[i].id = baseId + "-" + i;
  }
  this.setData({
   loadingCount: images.length,
   images: images
  });
 }
})