如何检查Subject是否不为null？

Question

我有以下代码：

@Injectable()
export class FilterRegister {
  public registerFilter: Subject<any> = new Subject();
  public registerFilterParameters: Subject<any> = new Subject();

  getFilter(): Observable<any> {
    return this.registerFilter.asObservable();
  }

  getParameters(): Observable<any> {
    return this.registerFilterParameters.asObservable();
  }
}

如果registerFilter不为null，如何检入模板？喜欢：

<div *ngIf="!!registerFilter"></div>

Answer 1

由于可以观察到registerFilter，因此您需要使用async管道或使用subscribe

两个

registerFilter$: Observable<any>

this.registerFilter$ = service.getFilter();

<div *ngIf="(registerFilter$ | async)"></div>  

或

registerFilter : any;

service.getFilter().Subscribe((value) => this.registerFilter = value);

<div *ngIf="registerFilter"></div>  

建议

请注意，这将是更清洁的服务实现。

export class FilterRegister {
  registerFilter$ : Observable<any> = this.registerFilter.asObservable();
  registerFilterParameters$ : Observable<any> = this.registerFilterParameters.asObservable();
  private registerFilter: Subject<any> = new Subject();
  private registerFilterParameters: Subject<any> = new Subject();

  foo() {
    this.registerFilter.next('value');
  }
}