JavaScript实现无穷滚动加载数据

2019-11-19 16:39:23

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来源：转载

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首先实现滚动要借助onscroll事件处理程序。

无穷滚动就是滑动滚动条，实现数据块的无穷加载。

我们以瀑布流的布局来实现无穷加载。瀑布流就是一些等宽不等高的数据块布局。在滚动条下拉时，它会进行加载。那么问题就是在判断什么时候应该加载。

我们首先应该明白瀑布流布局的特点。它将下一个图片总是放在当前列数最低的那一列。所以当加载最后一个蓝色的图片时，也就无疑是最后一个图片了。所以要判断该图片加载到什么程度来触发滚动事件。
图上灰色的表示页面的大小，后面蓝色边框表示窗口的大小。当拖动滚动条时，灰色部分上移。我们希望页面最后一个图片（蓝色图片）加载一半时触发滚动事件。那么就要形成参照。

下来写代码：

//检测是否具备滚动条加载数据块的条件function checkScrollSlide(){ var oparent = document.getElementById('main'); var oBoxs = getByClass(oparent,'box'); var scrollH = document.body.scrollTop || document.documentElement.scrollTop + document.body.clientHeight || document.documentElement.clientHeight; var lastBoxH = oBoxs[oBoxs.length - 1].offsetTop + Math.floor(oBoxs[oBoxs.length - 1].offsetHeight/2); return (lastBoxH < scrollH )? true : false;}

getClass是根据类名查找元素集合的自己写的函数，待会儿会附上源码

我们要进行加载的数据块的格式是这样的.每个图片被一个class= pic的div包裹。最后整体属于父元素main

<div id = "main"> <div class = "box">  <div class = "pic">   <img src = "images/0.jpg">  </div> </div> <div class = "box">  <div class = "pic">   <img src = "images/1.jpg">  </div> </div> <div class = "box">  <div class = "pic">   <img src = "images/2.jpg">  </div> </div><div>

首先我们要加载的数据块应该是从后台传过来的，在这里我们用json模拟一下就可以：

var DataIn = {"data":[{"src":'0.jpg'},{"src":'1.jpg'},{"src":'2.jpg'},{"src":'3.jpg'},{"src":'4.jpg'},{"src":'5.jpg'}]};

比如这个就是后台传过来的数据。

上面的函数返回一个布尔值，当为true时，触发滚动事件。

 window.onscroll = function(){ var oparent = document.getElementById('main'); //当满足加载条件时，就要向页面中加载数据块 if(checkScrollSlide){  for(var i = 0; i< DataIn.data.length; i++){    var oBox = document.createElement('div');    oBox.className = 'box';    oparent.appendChild(oBox);    var opic = document.createElement('div');    opic.className = 'pic';    oBox.appendChild(opic);    var oImg = document.createElement('img');    oImg.src = './images/'+DataIn.data[i].src;    opic.appendChild(oImg);   }   waterFull('main','box');  } }}

附上源码：

css和html

<!DOCTYPE html><html><head><meta charset = "utf-8" /><script src = "./jswaterfll.js"></script> <title>瀑布流布局</title> <style type="text/css"> *{ padding: 0px; margin: 0px; } #main{ position: relative; } .box{/* display: inline-block;*/ padding: 15px 0px 0px 15px; float: left; } .pic{ padding: 10px; border-radius: 5px; border:1px solid #ccc; box-shadow: 0 0 5px #ccc; } .pic img{ width: 165px; height: auto; } </style></head><body><div id = 'main'> <div class = "box"> <div class = "pic">  <img src = "images/3.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/4.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/20.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/21.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/2.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/3.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/4.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/5.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/6.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/7.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/8.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/9.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/10.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/11.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/17.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/18.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/19.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/4.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/5.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/6.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/7.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/8.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/11.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/12.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/13.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/14.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/15.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/16.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/17.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/18.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/19.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/20.jpg"> </div> </div> <div class = "box"> <div class = "pic">  <img src = "images/21.jpg"> </div> </div></div></body></html>

js代码：

window.onload = function(){ waterFull('main','box'); var DataIn = {"data":[{"src":'0.jpg'},{"src":'1.jpg'},{"src":'2.jpg'},{"src":'3.jpg'},{"src":'4.jpg'},{"src":'5.jpg'}]}; window.onscroll = function(){  var oparent = document.getElementById('main');  if(checkScrollSlide){   for(var i = 0; i< DataIn.data.length; i++){    var oBox = document.createElement('div');    oBox.className = 'box';    oparent.appendChild(oBox);    var opic = document.createElement('div');    opic.className = 'pic';    oBox.appendChild(opic);    var oImg = document.createElement('img');    oImg.src = './images/'+DataIn.data[i].src;    opic.appendChild(oImg);   }   waterFull('main','box');  } }}function waterFull(parent,children){ var oParent = document.getElementById(parent); //var oBoxs = parent.querySelectorAll(".box");  var oBoxs = getByClass(oParent,children); //计算整个页面显示的列数 var oBoxW = oBoxs[0].offsetWidth; var cols = Math.floor(document.documentElement.clientWidth/oBoxW); //设置main的宽度，并且居中 oParent.style.cssText = 'width:'+oBoxW * cols +'px; margin: 0 auto'; //找出高度最小的图片，将下一个图片放在下面 //定义一个数组，存放每一列的高度，初始化存的是第一行的所有列的高度 var arrH = []; for(var i = 0; i< oBoxs.length ; i++){  if(i < cols){   arrH.push(oBoxs[i].offsetHeight);  }  else{   var minH = Math.min.apply(null,arrH);   var minIndex = getMinhIndex(arrH,minH);   oBoxs[i].style.position = 'absolute';   oBoxs[i].style.top= minH + 'px';   //oBoxs[i].style.left = minIndex * oBoxW + 'px';    oBoxs[i].style.left = oBoxs[minIndex].offsetLeft+'px';   arrH[minIndex] += oBoxs[i].offsetHeight;   } }}function getByClass(parent,className){ var boxArr = new Array();//用来获取所有class为box的元素 oElement = parent.getElementsByTagName('*'); for (var i = 0; i <oElement.length; i++) {  if(oElement[i].className == className){   boxArr.push(oElement[i]);  } }; return boxArr;}//获取当前最小值得下标function getMinhIndex(array,min){ for(var i in array){  if(array[i] == min)   return i; }}//检测是否具备滚动条加载数据块的条件function checkScrollSlide(){ var oparent = document.getElementById('main'); var oBoxs = getByClass(oparent,'box'); var scrollH = document.body.scrollTop || document.documentElement.scrollTop + document.body.clientHeight || document.documentElement.clientHeight; var lastBoxH = oBoxs[oBoxs.length - 1].offsetTop + Math.floor(oBoxs[oBoxs.length - 1].offsetHeight/2); return (lastBoxH < scrollH )? true : false;}

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