使用jQuery数据表中的列过滤器下拉列表修复标头

Question

我有一个带有固定标题和列过滤器下拉列表的数据表，这些数据表在悬停时会延伸。但是下拉菜单并没有按照他们的意愿延伸。我已经跟踪了表初始化中的scrollY和scrollX问题。如果我删除两个滚动命令，下拉列表工作正常，但标题不再修复，我需要修复它。我已经尝试使用sScrollXInner和sScrollYInner，它允许列过滤器下拉列表工作，但同样，标题不再修复。我还在CSS中尝试了一些带有'relative'的'z-index'选项，但似乎没什么用。有任何想法吗？

html：

<table id="example" class="display" cellspacing="0" width="100%">
      <thead>
        <tr>
          <th>Name</th>
          <th>Position</th>
          <th>Office</th>
          <th>Age</th>
        </tr>
      </thead>
      <tfoot>
        <tr>
          <th>Name</th>
          <th>Position</th>
          <th>Office</th>
          <th>Age</th>
        </tr>
      </tfoot>
      <tbody>
        <tr>
          <td>Tiger Nixon</td>
          <td>System Architect</td>
          <td>Edinburgh</td>
          <td>61</td>
        </tr>
        <tr>
          <td>Garrett Winters</td>
          <td>Accountant</td>
          <td>Tokyo</td>
          <td>63</td>
        </tr>
        <tr>
          <td>Ashton Cox</td>
          <td>Junior Technical Author</td>
          <td>San Francisco</td>
          <td>66</td>
        </tr>
        <tr>
          <td>Cedric Kelly</td>
          <td>Senior javascript Developer</td>
          <td>Edinburgh</td>
          <td>22</td>
        </tr>
        <tr>
          <td>Airi Satou</td>
          <td>Accountant</td>
          <td>Tokyo</td>
          <td>33</td>
        </tr>
        <tr>
          <td>Brielle Williamson</td>
          <td>Integration Specialist</td>
          <td>New York</td>
          <td>61</td>
        </tr>
        <tr>
          <td>Herrod Chandler</td>
          <td>Sales Assistant</td>
          <td>San Francisco</td>
          <td>59</td>
        </tr>
        <tr>
          <td>Rhona Davidson</td>
          <td>Integration Specialist</td>
          <td>Tokyo</td>
          <td>55</td>
        </tr>
        <tr>
          <td>Colleen Hurst</td>
          <td>Javascript Developer</td>
          <td>San Francisco</td>
          <td>39</td>
        </tr>

      </tbody>
 </table>

脚本：

  $(document).ready(function() {
  function cbDropdown(column) {
    return $('<ul>', {
      'class': 'cb-dropdown'
    }).appendTo($('<div>', {
      'class': 'cb-dropdown-wrap'
    }).appendTo(column));
  }

  $('#example').DataTable({

   scrollY: 'calc(100vh - 270px)', //  dictates height of container!
   scrollX: '100%',

    initComplete: function() {
      this.api().columns([0, 2]).every(function() {
        var TotChkbxs = 0;
        var TikdChkbxs = 0;
        var column = this;
        var ddmenu = cbDropdown($(column.header()))

          .on('change', ':checkbox', function() {

            var active;
            var vals = $(':checked', ddmenu).map(function(index, element) {
              active = true;
              return $.fn.dataTable.util.escapeRegex($(element).val());
            }).toArray().join('|');

            column
              .search(vals.length > 0 ? '^(' + vals + ')$' : '', true, false)
              .draw();
          });

        column.data().unique().sort().each(function(d, j) {

          var $label = $('<label>'),
            $text = $('<span>', {
              text: d
            }),

            $cb = $('<input>', {
              type: 'checkbox',
              value: d
            });

          $text.appendTo($label);
          $cb.appendTo($label);

          ddmenu.append($('<li>').append($label));

        });

      });

    }
  });

});

CSS：

.cb-dropdown-wrap {
  max-height: 80px;
  position: relative;
  height: 19px;
}

.cb-dropdown,
.cb-dropdown li {
  margin: 0;
  padding: 0;
  list-style: none;
  transition: 0.2s 0.23s height ease-in-out;
}

.cb-dropdown {
  position: absolute;
  z-index: 1;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: white;
  border: 1px solid blue;
}

.active .cb-dropdown {
  background: transparent;
}

.cb-dropdown-wrap:hover .cb-dropdown {
  /* Expand container */
  height: 200px;
  overflow: auto;
  transition: 0.15s 0.18s height ease-in-out;
}

.cb-dropdown li.active {
  background: white;
}

.cb-dropdown li label {
  display: block;
  position: relative;
  cursor: pointer;
  line-height: 20px;
  margin-bottom: 2px;
  border-style: solid;
  border-width: 1px 0px 1px 0px;
  border-color: #dedede;
}

.cb-dropdown li:last-child {
  padding-bottom: 12px;
}

.cb-dropdown li label>input {
  position: absolute;
  left: 0;
  top: 1px;
  width: 16px;
}

.cb-dropdown li label>span {
  display: block;
  margin-left: 25px;
  font-family: sans-serif;
  font-size: 12px;
  font-weight: normal;
  text-align: left;
}

.cb-dropdown li:nth-child(n+2):hover {
  background: #dedede;
}

table.dataTable thead .sorting,
table.dataTable thead .sorting_asc,
table.dataTable thead .sorting_desc,
table.dataTable thead .sorting_asc_disabled,
table.dataTable thead .sorting_desc_disabled {
  background-position: 100% 10px;
}

小提琴：https://jsfiddle.net/5djcocuL/