如何让Timepicker出现在Angular的下拉列表中？

npm install ngx-bootstrap --save

import { TimepickerModule } from 'ngx-bootstrap/timepicker';

@NgModule({
  imports: [
    // 其他模块
    TimepickerModule.forRoot()
  ],
  // 其他配置
})
export class AppModule { }

<div class="dropdown">
  <button class="btn btn-secondary dropdown-toggle" type="button" id="timepickerDropdown" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
    选择时间
  </button>
  <div class="dropdown-menu" aria-labelledby="timepickerDropdown">
    <timepicker [(ngModel)]="selectedTime"></timepicker>
  </div>
</div>