Behaviour subject initial value null?
AngularTypescriptRxjsAngular Problem Overview
private customer: Subject<Object> = new BehaviorSubject<Object>(null);
setCustomer(id, accountClassCode) {
this.customer.next({'id': id, 'accountClassCode': accountClassCode});
}
getCustomer() {
return this.customer.asObservable();
}
I'm using this part of code but I'm getting an error that can not find id of null. Is there any solution to get initial value that is not null?
Angular Solutions
Solution 1 - Angular
The purpose of BehaviorSubject
is to provide initial value. It can be null
or anything else. If no valid initial value can be provided (when user id isn't known yet), it shouldn't be used.
ReplaySubject(1)
provides a similar behaviour (emits last value on subscription) but doesn't have initial value until it is set with next
.
It likely should be
private customer: Subject<Object> = new ReplaySubject<Object>(1);
Solution 2 - Angular
Try structuring this way your service:
Service:
@Injectable()
export class MyService {
customerUpdate$: Observable<any>;
private customerUpdateSubject = new Subject<any>();
constructor() {
this.customerUpdate$ = this.customerUpdateSubject.asObservable();
}
updatedCustomer(dataAsParams) {
this.customerUpdateSubject.next(dataAsParams);
}
}
Remember to add MyService
to providers.
Where you update your client (if this is the case), you do something like this:
Component (The one that triggers):
constructor(private myService: MyService) {
// I'll put this here, it could go anywhere in the component actually
// We make things happen, Client has been updated
// We store client's data in an object
this.updatedClient = this.myObjectWithUpdatedClientData; // Obj or whatever you want to pass as a parameter
this.myService.updatedCustomer(this.updatedClient);
}
Component (The one that is Subscribed):
this.myService.customerUpdate$.subscribe((updatedClientData) => {
// Wow! I received the updated client's data
// Do stuff with this data!
}
);
From what I understood, you are trying to pass data from 1 component to another. You get your Client's data and send it over your App to another component, right? That's why I posted this solution.
If you are interested in other types of subscriptions, read this:
Solution 3 - Angular
I have found many cases where I want the simplicity of ReplaySubject(1)
but also want the value
property of BehaviorSubject
, i.e. it stores your most recent value for retrieval without having to subscribe. And using BehaviorSubject
was always annoying given the need for an initial value that gets broadcast, a condition I rarely wanted. To that end I created my own CurrentSubject
.
import { ReplaySubject } from "rxjs";
export class CurrentSubject<T> extends ReplaySubject<T> {
value: T;
set(value?: T) {
this.value = value;
this.next(value);
}
}
I wanted to override the next
method but I couldn't get that to work for some reason, so I settled on a method called set
. My override attempt looked like this...
export class CurrentSubject<T> extends ReplaySubject<T> {
value: T;
next(value?: T) {
this.value = value;
super.next(value);
}
}
I don't know why overriding didn't work.
Solution 4 - Angular
Since the object can be null, a better choice is to infer the type like this
private customer = new BehaviorSubject<Customer|null>(null);
Solution 5 - Angular
Another way is to use pipe to filter until a non-null value is received. It can be done with takeWhile also.
.pipe(filter(val => !!val)).subscribe(x => {});