docs: function createThead(createFlag) {
      var oThis = this,
          visibleIndex = 0,
          gridCompColumnArr,
          trStyle = '',
          thLevelClass = '';
      if (this.options.maxHeaderLevel > 1) {
          trStyle = 'style="height:' + (this.headerHeight - 1) + 'px;"';
          thLevelClass = ' u-grid-header-level-th ';
      }
      var htmlStr = '<tr role="row" ' + trStyle + '>';
      if (createFlag == 'fixed') {
          gridCompColumnArr = this.gridCompColumnFixedArr;
      } else {
          gridCompColumnArr = this.gridCompColumnArr;
      }
      $.each(gridCompColumnArr, function (i) {
          var vi = visibleIndex,
              displayStyle = '';
          if (this.options.visible == false) {
              vi = -1;
              displayStyle = 'style="display:none;"';
          } else {
              visibleIndex++;
          }
  
          // 低版本浏览器不支持th position为relative，因此加入空div
          htmlStr += '<th role="columnheader" data-filed="' + this.options.field + '" rowspan="1" class="u-grid-header-th ' + thLevelClass + '" ' + displayStyle + 'field="' + this.options.field + '" index="' + i + '" visibleIndex="' + vi + '"><div style="position:relative;" class="u-grid-header-div">';
          var colorStype = '';
          if (this.options.headerColor || oThis.options.headerHeight) {
              var headerC = '';
              var headerH = '';
              if (this.options.headerColor) headerC = 'color:' + this.options.headerColor + ';';
              if (oThis.options.headerHeight) headerH = 'height:' + oThis.options.headerHeight + 'px;line-height:' + oThis.options.headerHeight + 'px;';
              colorStype = 'style="' + headerC + headerH + '"';
          }
          var requiredHtml = '';
          if (this.options.required) {
              requiredHtml = '<span style="color:red;">*</span>';
          }
          htmlStr += '<div class="u-grid-header-link" field="' + this.options.field + '"  style="text-align:' + this.options.textAlign + '" ' + colorStype + '>' + this.options.title + requiredHtml + '</div>';
          /*if(oThis.options.columnMenu && createFlag != 'fixed'){
              // 创建右侧按钮图标
              htmlStr += '<div class="u-grid-header-columnmenu uf uf-navmenu-light " field="' + this.options.field + '" style="display:none;"></div>';
          }*/
          htmlStr += '</div></th>';
      });
  
      htmlStr += '</tr>';
      return htmlStr;
  }