我目前正在尝试将Observable
转换为Promise。但是当我调用该方法时,什么也没有发生。我正在使用Angular 6。
public create(form: StoryForm): Promise<void | string> {
const key: string = this.afStore.createId();
return this.auth.authState.pipe(map(res =>
<Story>{
title: form.title, content: form.content, createdAt: new Date(), sid: key,
uid: res.uid, username: res.displayName
}
)).toPromise().then((story: Story) =>
this.afStore.doc(`stories/${key}`).set(story).catch(err => err.message));
}
public save() {
this.triedToSave = true;
if (this.storyForm.valid) {
this.storyService.create(this.storyForm.value)
.then(() => this.router.navigate(['/stories']))
.catch((err: string) => this.notify.danger(err));
}
}
保存应该做的是浏览或至少显示错误。
如何实现authstate:它返回可观察到的一些用户信息。它是在其他服务中实现的,如下所示:
public get authState(): Observable<firebase.User> {
return this.afAuth.authState;
}
让我感到困惑的是,如果我使用模拟对象却突然无法工作:
public create(form: StoryForm) {
const key: string = this.afStore.createId();
return of({uid: 'blubb', displayName: 'kdsjf', photoUrl: 'kjdfkjfd'}).pipe(map(user => {
return {
title: form.title, content: form.content, createdAt: new Date(), sid: key,
uid: user.uid, username: user.displayName, photoUrl: user.photoURL
} as Story;
})).toPromise();
}
但是我想知道为什么toPromise在上面的示例中不起作用...
答案 0 :(得分:1)
我猜测什么也没发生,因为当您触发save方法时,authState不会发出任何结果。显然,您希望authState observable或Subject总是会触发一些输出,只有在特定情况下才如此。
下面的代码创建一个-new- observable来侦听authState。
return this.auth.authState.pipe(map(res =>
<Story>{
title: form.title, content: form.content, createdAt: new Date(), sid: key,
uid: res.uid, username: res.displayName
}
)).toPromise().then((story: Story) =>
this.afStore.doc(`stories/${key}`).set(story).catch(err => err.message));
该代码仅由save方法触发。我的猜测是authState是可观察的或主题。您的代码仅在authState传递新值后才起作用-触发save方法之后。
使用模拟对象的代码可以工作,因为您创建了一个可观察的对象,该对象立即发出该值。
如果authState是主题,则将其替换为ReplaySubject(1)
如果它是可观察的,则需要像这样将其作为ReplaySubject发布:
authState.pipe(
publishReplay(1),
refCount()
);
要完全了解发生了什么,请阅读此文章: https://blog.mindorks.com/understanding-rxjava-subject-publish-replay-behavior-and-async-subject-224d663d452f
这是一篇Java文章,但适用相同的原理。
但是说实话,当我看到人们使用toPromise方法时,我感到畏缩:) 如果按预期使用rxjs,您会学得更快!
如果我要编写这段代码,它将看起来像这样:
public save$: Subject<StoryForm> = Subject<StoryForm>();
private destroy$: Subject<any> = new Subject();
ngOnDestroy(): void {
this.destroy$.next();
}
onInit() {
// the (click) eventhandler in your GUI should call save$.next(storyForm)
// this will trigger this statement
this.save$.pipe(
// withLatestFrom will fetch the last value from an observable,
// it still needs to be a ReplaySubject or ReplaySubject for this to work though!
// it will pass an array down the pipe with the storyForm value, and the last value from authState
withLatestFrom(this.auth.authState),
// switchMap does the actual work: note that we do not return a value,
// but an observable that should that return a value soon, that is why we need switchMap!
switchMap(([storyForm, authInfo]) => {
// i am assuming the "set" method returns an observable
// if it returns a Promise, convert it using fromPromise
return this.afStore.doc(`stories/${key}`).set(story).pipe(
// catchError needs to be on your api call
catchError(err => console.log(err))
);
}),
// this will kill your subscriptino when the screen dies
takeUntil(this.destroy$)
).subscribe(value => {
// "value" will be the return value from the "set" call
this.router.navigate(['/stories']);
}
}