Angular2-带有下拉菜单NGbDropDown或简单选择下拉菜单的虚拟滚动条

有没有简单的选择下拉列表或ngbDropdown的工作方式。这就是代码的外观。

<virtual-scroll [items]="items" (update)="scrollItems = $event" (end)="fetchMoreRecords($event)">
              <div class="dropdown-menu" ngbDropdownMenu>
                <h5 class="dropdown-header">Heading</h5>
                <div class="dropdown-item" *ngFor="let item of scrollItems">
                    item.itemValue
                </div>
              </div>
            </virtual-scroll>

<virtual-scroll [items]="items" (update)="scrollItems = $event" (end)="fetchMoreRecords($event)">
          <select id="selectId" [formControlName]="virtualDropdown" class="custom-select"
            required>
            <option *ngFor="let item of scrollItems" [ngValue]="item.itemValue">
              item.itemValue
            </option>
          </select>
        </virtual-scroll>

但它似乎不起作用。有什么想法吗?提前谢谢。