Question

我的行为主体状态低于标准，并且已存储为studentNo来自其他组件的值，

const initialState: any = {
   studentNo: '',
}
private _state$: BehaviorSubject<any> = new BehaviorSubject<any>(initialState);
get state$(): Observable<any> { return this._state$; }

private _requestStudent$: Subject<void> = new Subject<void>();

然后我在服务文件构造器块中监听this.requestStudent$主题，

constructor(): void {
   this._requestStudent$.pipe(
      tap(this.state$),//Is this correct way to pass state$ value to below switchMap?,
      switchMap(this.requestStudentDetail.bind(this)),
   ).subscribe(this._studentList$);
}

requestStudentDetail(state: any): Observable<any> {
   return this.http....// I got the undefined value, If i print state.studentNo value here
}

public getStundentDetail(): void {// i called this function from component A
   this._requestStudent$.next();
}

如何在没有订阅this.state$的情况下将状态值（studentNo）传递给http api服务功能。

Answer 1

好吧，您可能想先switchMap声明状态？

this._requestStudent$.pipe(
  switchMap(this.state$),
  switchMap((studentNumber) => this.requestStudentDetail(studentNumber)),
).subscribe(this._studentList$);

Answer 2

我们可以使用'withLatestFrom'rxjs运算符从主题中获取值，因此我可以重新编写如下代码，

this._requestStudent$.pipe(
  withLatestFrom(this.state$),
  switchMap(this.requestStudentDetail.bind(this)),
).subscribe(this._studentList$);

A.withLatestFrom（B）用于在可观察到的A发出时从可观察到的B获取值，例如数组[a，b]格式。

如何将主题值传递到管道内的switchMap？

2 个答案: