[英]angular 2 rxjs subscribe to observable code not executing
我有一个 angular 应用程序使用 rxjs 订阅从主题实例化的可观察对象。
下面是我的 app.service.ts
private subjectGreeting: Subject<Greeting>; //Subject declared
resGreeting: Observable<Greeting>; //Observable declared
authenticate(credentials, callback) {
const headers = new HttpHeaders({ Authorization : 'Basic ' + btoa(credentials.username + ':' + credentials.password)
});
return this.http.get<Greeting>('http://localhost:8080/user', {headers},).subscribe(response => {
console.log('Inside app service authenticate');
if (response) {
this.subjectGreeting = new Subject(); //subjectGreeting being instantiated
this.resGreeting = this.subjectGreeting.asObservable(); //resGreeting being assigned asObservable()
this.subjectGreeting.next(response); //next response being assigned to subjectGreeting
}
callback();
});
在组件方面,我有一个登录组件,它从上述服务调用验证 function:
以下是组件代码:
login() {
console.log('inside login');
this.app.authenticate(this.credentials, () => {
this.app.authenticated = true;
this.childComponent.refreshFromParent(); //refresh child component (do a subscription after authentication)
// Redirect the user
this.router.navigate(['../home']);
} );
return false;
}
login() function 也调用 refreshFromParent() 如下:
refreshFromParent(): void{
console.log('home component refresh from parent');
if(this.app.resGreeting){
this.subscriptionGreeting = this.app.resGreeting.subscribe(r => { ***//This subscription code is not executing despite the fact that it is being called after authentication***
console.log('inside greeting subscription');
if(r){
this.greeting = r;
this.authenticated = true;
}
});
}
}
最后,组件的 html 如下:
<a routerLink="./" routerLinkActive="active"
[routerLinkActiveOptions]="{ exact: true }">Welcome Home!</a>
<div [hidden]="(authenticated)">
<p *ngIf="greeting">The ID is {{greeting.id}}</p>
<p *ngIf="greeting">The content is {{greeting.content}}</p>
</div>
<div [hidden]="!(authenticated)">
<p>Login to see your greeting</p>
</div>
<router-outlet></router-outlet>
出于某种原因,我没有得到任何 output {{greeting.id}} 和 {{greeding.content}}
使用BehaviorSubject
而不是Subject
。
private subjectGreeting: BehaviorSubject<Greeting> = new BehaviorSubject<Greeting>(null);
resGreeting: Observable<Greeting> = this.subjectGreeting.asObservable();
订阅Subject
将在订阅后收到下一个值。 因此,如果您在this.subjectGreeting.next(..)
之后订阅Subject
,则订阅不会运行到next
将再次调用,因为您订阅之后。
通过切换到BehaviorSubject
,您在订阅时总能获得最新信息。
https://devsuhas.com/2019/12/09/difference-between-subject-and-behaviour-subject-in-rxjs/
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