jQuery：实现图片按需加载的方法，当要显示内容的高度超过了页面的高度，按需加载，根据滚动条的位置来判断页面显示的内容

Posted 2021-01-31 fuhuirong

实现图片按需加载的方法，当要显示内容的高度超过了页面的高度，按需加载，根据滚动条的位置来判断页面显示的内容

这个类似于京东或淘宝页面，根绝页面的滚动，显示下面的内容

如下图所示，一开始并不是所有的图片都显示，当滚动条移动到页面最下面的时候，再显示下面的内容

 

解决思路：通过判断滚动条是否滚动到了页面的最下面，如果滚动到了页面的最下面，则重新加载图片

知识点：1.offset() 方法返回或设置匹配元素相对于文档的偏移（位置）

返回第一个匹配元素的偏移坐标。

该方法返回的对象包含两个整型属性：top 和 left，以像素计。此方法只对可见元素有效。

2.scrollTop()：方法返回或设置匹配元素的滚动条的垂直位置。返回滚动条的垂直位置

innerHeight(): 返回滚动条的高度，当移动滚动条的位置，innerHeight()的值不变

scrollHeight: 其实不是“滚动条的高度"，而是表示滚动条需要滚动的高度，即内部div的高度

参考链接：https://blog.csdn.net/wu_dada/article/details/78094991

实现方法是判断是否到了页面的最底部：

$(‘#thumbnailcontainer, .scroll-table-wrap‘).on(‘scroll‘, function () {
          if (loadedImages >= maximumLoadedImages) {
            if ($(this)[0].scrollHeight - $(this).innerHeight() - $(this).scrollTop() < 5) {
              _messagebox.newNotify2(GlobalStringsForAssets.MAXIMUM_LOADED_ASSETS, "", -1);
            }
            return;
          }

          if ($(this).scrollTop() + $(this).innerHeight() >= $(this)[0].scrollHeight - 60) {
            if (inDelay) { return; }
            CallGetImages($(this), false);
          }
        })

function CallGetImages($ctl, delayed) {
        if (delayed) {
          if ($ctl.scrollTop() + $ctl.innerHeight() >= $ctl[0].scrollHeight - 60) {
            GetImages();
          }

          inDelay = false;
          return;
        }

        inDelay = true;
        setTimeout(function () {
          CallGetImages($ctl, true);
        }, 100);
      }

function GetImages() {
        var timer = null;
        if (getImagesXhr != null) {
          getImageQueued = true;
          return;
        }

        var columnQueryData = CollectQueryData();
        var sortdata;
        if (modelPageType === ‘brand‘) {
          sortdata = $(‘#brandSortFilter > button‘).attr(‘sortcolumn‘) + ‘,‘ + $(‘#brandsortdirection‘).attr(‘sortdirection‘);
        }
        else {
          sortdata = $(‘#sortFilter > button‘).attr(‘sortcolumn‘) + ‘,‘ + $(‘#sortdirection‘).attr(‘sortdirection‘);
        }

        var searchTerm = ‘‘;
        if (modelPageType == ‘brand‘)
          searchTerm = $(‘#brandsearchbox‘).val().trim();
        else
          searchTerm = $(‘#searchbox‘).val().trim();
        var searchTags = null;
        if (modelPageType !== ‘brand‘)
          searchTags = $(‘#additionalTags‘).autocomplete("getTags");
        var currentSearch = JSON.stringify({ Columns: columnQueryData, SearchTerm: searchTerm, Tags: searchTags, Sorting: sortdata, PageType: pageType });
        if (lastSearch == currentSearch && getImagesXhr !== null) {
          // Already running a query. Wait until it finishes.
          return;
        }

        var newSearch = false;
        if (lastSearch != currentSearch) {
          ClearSearch();

          newSearch = true;
          lastSearch = currentSearch;

          if (getImagesXhr !== null) {
            getImagesXhr.abort();
            getImagesXhr = null;
            if (modelPageType == ‘brand‘ && getCollectionsXhr !== null) {
              getCollectionsXhr.abort();
              getCollectionsXhr = null;
            }
          }

          lastClickedAssetId = ‘‘;
          selectedCnt = 0;
        }

        if (newSearch || cachedAssets == null) {

          clearTimeout(timer);
          $(‘.centered‘).show();
          imagesQueryData = { Skip: loadedImages, Batch: 50, Columns: columnQueryData, SearchTerm: searchTerm, Tags: searchTags, Sorting: sortdata, PageType: pageType };
          getImagesXhr = $.ajax({
            url: ‘/Assets/GetImages‘,
            type: ‘POST‘,
            dataType: ‘json‘,
            data: JSON.stringify(imagesQueryData),
            contentType: ‘application/json; charset=utf-8‘,
            success: function (result) {
              if (result.success) {
                imageData = result.data;
                ShowAssets(imageData);
                showMainSearchList(imageData, searchTerm,"#mainSearchBoxList");
              } else {
                console.log("error");
              }
              getImagesXhr = null;
            },
            error: function (XMLHttpRequest, textStatus, errorThrown) {
              getImagesXhr = null;
            },
            async: true,
            processData: true,
            complete: function () {
              timer=setTimeout("$(‘.centered‘).hide()", 400);
              getImagesXhr = null;
              if (getImageQueued) {
                getImageQueued = false;
                GetImages();
              }

              if (newSearch || parseInt($(‘.numberOfSearch‘).text()) < loadedImages) {
                GetAssetCount(JSON.stringify({ Columns: columnQueryData, SearchTerm: searchTerm, Tags: searchTags, Sorting: sortdata, PageType: pageType }));
              }

              CacheAssets(columnQueryData, searchTerm, searchTags, sortdata, pageType);
            }
          });
        } else {
          imageData = cachedAssets;
          cachedAssets = null;
          ShowAssets(imageData);

          if (parseInt($(‘.numberOfSearch‘).text()) < loadedImages) {
            GetAssetCount(JSON.stringify({ Columns: columnQueryData, SearchTerm: searchTerm, Tags: searchTags, Sorting: sortdata, PageType: pageType }));
          }

          CacheAssets(columnQueryData, searchTerm, searchTags, sortdata, pageType);
        }
      }

完整的代码为：