web手机端或App中经常会有下拉刷新，上拉加载这些功能。
微信小程序中如何实现下拉刷新，上拉加载的功能。
实现思路：
1.监听界面的下拉刷新事件和上拉加载事件
bindscrolltolower 监听上拉加载
bindscrolltoupper 监听下拉刷新
2.下拉刷新时清空数据列表，并重新请求数据进行界面展示。
3.上拉加载增量请求数据，增量增加数据列表，增量界面展示
效果图：
实现代码：
WaterFall.wxml:
<!--pages/WaterFall/WaterFall.wxml--> <view> <image wx:for="{{images}}" wx:key="id" src="https://www.jb51.net/{{item.pic}}" bindload="onImageLoad"></image> </view> <scroll-view scroll-y="true" bindscrolltolower="loadImages" bindscrolltoupper="PullDownRefresh"> <view> <view> <view wx:for="{{col1}}" wx:key="id"> <image src="https://www.jb51.net/{{item.pic}}"></image> </view> </view> <view> <view wx:for="{{col2}}" wx:key="id"> <image src="https://www.jb51.net/{{item.pic}}"></image> </view> </view> </view> </scroll-view>
WaterFall.js：
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 }); } })