angular – 如何在Reactive Form上使用ng-bootstrap Typeahead组件

我正在尝试在带有Angular 2的Reactive Form上使用Ng-bootstrap Typeahead组件,在查看 Typeahead’s documentation上的示例代码后,我无法使其工作.

目前,我有类似的东西：

<input type="text" aria-describedby="cityValid" class="form-control" id="inputCity" [formControl]="userForm.controls.city" [ngbTypeahead]="search">

使用与示例代码几乎相同的搜索功能,但它会因以下堆栈跟踪而失败

error_handler.js:53 TypeError: CAnnot read property 'subscribe' of undefined
at NgbTypeahead._subscribeToUserInput (typeahead.js:158)
at NgbTypeahead.ngOnInit (typeahead.js:52)
at DebugAppView._View_UserFormComponent0.detectChangesInternal (UserFormComponent.ngfactory.js:1093)
at DebugAppView.AppView.detectChanges (view.js:271)
at DebugAppView.detectChanges (view.js:376)
at DebugAppView.AppView.detectViewChildrenChanges (view.js:297)
at DebugAppView._View_ExecutionFormComponent3.detectChangesInternal (ExecutionFormComponent.ngfactory.js:551)
at DebugAppView.AppView.detectChanges (view.js:271)
at DebugAppView.detectChanges (view.js:376)
at DebugAppView.AppView.detectContentChildrenChanges (view.js:289)

我究竟做错了什么？如果有一个关于如何在Reactive Forms上使用Ng-bootstrap组件的一般指南会很棒,因为该示例基于基于模板的示例.

谢谢！

searchCity (text$: Observable<String>) {
  text$
  .debounCETime(200)
  .disTinctUntilChanged()
  .map(term => term.length < 2 ? []
    : cities.filter(v => new RegExp(term,'gi').test(v)).splice(0,10));
}