JavaScript implements waterfall flow loading image principle

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JavaScript implements waterfall flow loading image principle_javascript skills

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May 16, 2016 pm 03:16 PM

Let’s talk about the general principle, let’s take the picture first:

Function description:

Load different data according to the attribute values of different menus
Pull down the scroll bar to a certain position to preload the image, and render the html when the scroll bar is pulled to the bottom;
Move the mouse to the menu to switch between various picture lists;
Move the mouse over the picture list to display detailed information;

Technical implementation plan:

Let’s first sort out the process from loading to display:
1. Load data
2. Splice HTML and write it to the page
3. Check whether all the img in the HTML just written have been loaded. If so, go to 5, otherwise go to 4
4. Wait for the image to load
5. Calculate the position of each element

The biggest headache at the beginning was how to position it. Later, after a friend’s guidance, I finally solved it: calculate how many columns of pictures there are in total and put the height of each column into an array. Whenever an image is loaded, search for the smallest value in the array, and set the top of the current image to this value. After completion, add the height of the image to the smallest value in the array and return it to the array, in sequence. analogy.
PS: Because there are too many codes for this function, we can only do basic simple decomposition of the code:

// 创建用于记录每列高度的数组
_getLowestCol: function() {
  t._cols = new Array(5),min = 0;
  // 初始化为0
  for (var i = 0; i < t._cols.length; i++) {
    if (cols[i] < cols[min]) {
      min = i;
    }
    return min;
  }
},
_reposition: function() {
  t._grids.each(function(i, grid) {
    //先显示出来
    grid = $(grid).show();
    
    var height = grid.outerHeight(), min = t._getLowestCol();

    // 定位
    grid.animate({
      left: (t._colWidth + t._colSpacing) * min,
      top: t._cols[min],
      opacity: 1
    },1000);
    // 记录高度
    t._cols[min] += height;
  });

}

The second difficulty encountered during the development process is: as shown in the picture above, moving the mouse to the menu bar requires switching the image list, and waterfall flow is required to load different types of data. Therefore, we have to deal with how to execute the code request interface only once for each page when switching pages, instead of re-requesting the data interface every time the page is switched, and only perform the operation of switching the display list of pictures.
Considering that each menu has a custom attribute, this problem is easily solved: create an object to record whether the current menu has executed code, and if not, execute the request data.

var isLoad = {};//是否载入过
labelType.mouseover(function() {
  var i = $(this).index();
  var api = _this.attr('api');//接口标识
  
  if(! isLoad[ api ]){
    isLoad[ api ] = i;
    loadData(wrapper, api);
  }
  
});

The following is the full code:
html:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title></title>
<style type="text/css">
*{margin:0;padding:0;}
ul,li{  list-style-type:none;}
li img{width:100%;list-style:none;}
</style>
</head>
<body>
  <div class="photo_box">
    <ul id="container" style="border:1px solid #000;width:80%;height:600px;overflow:hidden;margin:0 auto;position: relative;">
    </ul>
    <div id="loading" class="loading" style="text-align: center;margin-top: 20px;font-size: 1.2em;">加载中...</div>
    <div id="more" class="more"style="text-align: center;margin-top: 20px;font-size: 1.2em;"><input type="button" value="更 多" id="clear" /></div>
  </div>
<script type="text/javascript" src="../../lib/seajs/sea.js"></script>
<script type="text/javascript" src="../../lib/base/1.0.x/base.js"></script>
<script type="text/javascript">
seajs.use(['lib/jquery/1.11.x/index.js', '_example/waterFall_1.1/waterfall.js'], function($, waterFall) {
  waterFall.init({
    container: $('#container'),
    dataURL: 'http://www.woxiu.com/index.php&#63;action=Index/Main&do=ApiZhuboGrade',
    dataType: 'jsonp',
    template: '<% for (var i = 0; i < data.length; i++) { %>' +
            '<li style="display: none;">' +
              '<img  src=" <%-data[i].room_img% alt="JavaScript implements waterfall flow loading image principle_javascript skills" > ">' +
            '</li>' + 
          '<% } %>',
    colWidth: 200,
    colSpacing: 10,
    rowSpacing: 15,
    page: 1,
    pageEnd: 8,
  });

  // 限制同时展示的页数
  var loadCounter = 1;
  function pageNum(){
    if (loadCounter >= 3) {
      $('#more').show();
      $('#loading').hide();
      return true;
    } else {
      loadCounter++;
      $('#more').hide();
      $('#loading').show();
    }
    return false;
  }
  $('#clear').click(function() {
    loadCounter = 1;
    waterFall._loadNext();
  });
});

</script>
</body>

js:

/**
 * 瀑布流布局组件类
 * @param {Object} options 组件设置
 *    @param {NodeList} options.container 瀑布流容器
 *    @param {String} options.dataURL 数据地址
 *    @param {String} [options.dataType='jsonp'] 数据类型，json或jsonp
 *    @param {String}  options.template 模板编辑
 *    @param {Number} [options.colWidth] 图片大小。
 *    @param {Number} [options.colSpacing] 列间隔。
 *    @param {Number} [options.rowSpacing] 行间隔。
 *    @param {Number} [options.page=1] 数据开始页码
 *    @param {Number} [options.pageEnd] 数据末尾页码

 * @pageNum() 函数，如果不需要现在加载也是，需要把函数里面的判断去掉。


 从加载到显示的流程

1. 加载数据
2. 拼接HTML写入到页面
3. 检查刚刚写入的HTML中的img是否全部加载完成，如果是，进入5、否则进入4
4. 等待图片加载完成
5. 计算每个元素的位置

 */
define(function(require, exports, module) {
  'use strict';
  
  var Tmpl = require('lib/tmpl/2.1.x/index.js'),
    $ = require('lib/jquery/1.11.x/index.js');

  var waterFall = {
    init: function(options) {
      var t = this;
      t._container = options.container;
      t._template = options.template;
      t._colWidth = options.colWidth;
      t._colSpacing = options.colSpacing;
      t._rowSpacing = options.rowSpacing;
      t.dataURL = options.dataURL;
      t.dataType = options.dataType;
      t.page = options.page;
      t.pageEnd = options.pageEnd;
      t._switch = false;

      //计算有几列 总宽度 / (列宽 + 列间隔)
      t._totalCols = parseInt(t._container.width() / (t._colWidth + t._colSpacing));

      // 创建用于记录每列高度的数组
      t._cols = new Array(t._totalCols);
      // 初始化为0
      for (var i = 0; i < t._cols.length; i++) {
        t._cols[i] = 0;
      }

      t._loadingPage = options.page || 0;
      t._loadNext(options);

      //下拉滚动条加载
      var lastTime = new Date().getTime();

      $(window).scroll(function() {

        if ( !t._switch ) {
          //判断是否滚动过快,在ie下
          var thisTime = new Date().getTime();

          if (thisTime - lastTime < 50) {
            console.log(thisTime - lastTime);
            lastTime = thisTime;
            return;
          }

          if ($(window).scrollTop() + $(window).height() >= document.documentElement.scrollHeight) {
            lastTime = thisTime;
            t._loadNext();
          }
        }
      });
    },
    //加载器
    _loadNext: function(t) {
      var t = this;

      t._switch = true;
      //请求数据
      if (!t.trigger) {
        $.ajax({
          url: t.dataURL,
          data: { page: ++t._loadingPage },
          dataType:t.dataType,
          success: function(response){
            
            t.trigger = t._completeLoading(response);

          },
          error:function(){console.log('Error! 请求有误');}
        });  
      }
      return false;
    },
    //加载完数据调用此函数
    _completeLoading: function(result) {
      var t = this;
      if (t._loadingPage >= t.pageEnd) {
        $('#more').hide();
        $('#loading').html('<p>已是最后一页了喔 ^_^ ^_^</p>');
        return true;
      }
      else {
        //if (!pageNum()) {
          t._add(result);
        //};
      }
      
      return false;
    },
    //添加格子
    _add: function(result) {
      var t = this, grids = '';
      //调用模板
      var content = Tmpl.render(t._template, {data:result.data});
      //原始定位
        t._grids = $(content).css({
          position: 'absolute',
          left: t._container.width(),
          top: t._container.height(), 
          width: t._colWidth,
          opacity: 0
        });

      //把Html添加到容器
      t._container.append(t._grids);

      // 执行一次_reposition，如果所有图片都加载完成，该方法返回true，否则返回false
      if ( !t._reposition() ) {
        // 有图片未加载完，监听onload和onerror
        t._grids.find('img').bind('load error', function() {
          this.loaded = true;
          // 有图片加载完成，再次执行_reposition
          if (t._grids) {
            t._reposition();
          }
        });
      }
    },
    // 此方法用于获取高度最低的列
    _getLowestCol: function() {
      var cols = this._cols, min = 0;
      for (var i = 1; i < cols.length; i++) {
        if (cols[i] < cols[min]) {
          min = i;
        }
      }
      return min;
    },
    //定位
    _reposition: function() {

      var t = this, allImgsLoaded = true;

      // 检测图片是否全部加载完成
      t._grids.find('img').each(function(i, img) {
        if (!img.loaded && !img.complete) {

          allImgsLoaded = false;
        }
        return allImgsLoaded;
      });

      if (allImgsLoaded) {
        t._grids.each(function(i, grid) {
          //先显示出来
          grid = $(grid).show();
          
          var height = grid.outerHeight(), min = t._getLowestCol();

          // 非第一行的时候，要加上行间隔
          if (t._cols[min]) { t._cols[min] += t._rowSpacing; }
          // 定位
          grid.animate({
            left: (t._colWidth + t._colSpacing) * min,
            top: t._cols[min],
            opacity: 1
          },1000);
          // 记录高度
          t._cols[min] += height;
        });
        // 重设外层容器高度为最高列高度
        t._container.css( 'height', Math.max.apply(Math, t._cols) );
        t._switch = false;
        delete t._grids;
      }

      return allImgsLoaded;
    },
  }

  return waterFall;
});

The above is the entire content of this article. I hope it will be helpful to everyone in learning javascript programming.

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