Angular subject subscription is not working

Question

I have a service ->

subject = new Subject<any>();

  constructor (){
    this.subject.next('hello');
  }

  getsubject():Observable<any>{
    return this.subject.asObservable();
  }

and component ->

name:string;
  subscription : Subscription;
  constructor(private serv:SService) {
    this.subscription=this.serv.getsubject().subscribe(message=>{console.log('hello');});
  }

as you can see, i'm passing hello message from service to subscribers, but in component subscriber is not getting that value, even it's not logging any word.

plunker example

@N1gthm4r3 See this answer about question ook like your question https://stackoverflow.com/a/43374509 may solve this issue — ahmed hamdy, May 27 '20 at 15:47

score 15 · Accepted Answer · answered Sep 20 '17 at 13:44

The observable probably fires from the constructor before the component subscribes to it. So the component misses the message.

Instead of putting this.subject.next('hello') in the constructor, make a method.

  sendMessage (){
    this.subject.next('hello');
  }

You can then call the this.serv.sendMessage() from the component, and it will already be subscribed.

Alternatively you can look into BehaviorSubject which will hold onto the most recent value, and give it right away when something subscribes to it.

score 3 · Answer 2 · answered Sep 20 '17 at 13:43

Its working. plunker you need to add this code. So subject will emit value if nobody subscribed to it at that time nobody will know that it emitted value. and when somebody subscribe it will not emit last value(BehaviorSubject will) .

 passToServ() {
   this.subject.next(2);
 }

score 1 · Answer 3 · answered Sep 18 '19 at 18:36

1

If your subscriber is component file, one of the reason can be disremembering of adding selector of your component somewhere in your application. You must register component for example in app.component.html.

answered Sep 18 '19 at 18:36

enyoucky

103
1
9

score 0 · Answer 4 · answered Jul 24 '23 at 05:25

In my case the issue was this:

let mySubject = new Subject<number>();
mySubject.next(1);
mySubject.subscribe(x => console.log("First Subscription : " + x));

which is wrong, as Subject does not keep history of values, the 1 value was getting lost as I was subscribing at last.

So I changed it to this to make it work.

let mySubject = new Subject<number>();
mySubject.subscribe(x => console.log("First Subscription : " + x));
mySubject.next(1);

Debug tip, add break points on next and subscribe and make sure the subscribe breaks at the last.

If this is not possible, just replace Subject with BehaviourSubject which can help to emit value at point you subscribe to it

Angular subject subscription is not working

4 Answers4