How to "subscribe" to variables instead of just use them?

[Audrey84]

I have a HomePage the app starts on. It starts loading some stuff in the background via a service and puts the data into a property in the service when done. The homepage also displays a list of stuff that is already available from the beginning. The ItemPage you get to when clicking on an item in the list displays the information it has, but also tries to load additional data from the service.

When the user is quick enough to be on the ItemPage while the background loading in the service finishes, the data is not updated with the incoming data as the ItemPage constructor only took out of the service what was there when it loaded.

How do I get this to automatically get the data from the service when it finished loading?
(And of course how should I handle the UI before this happens?)

(I have the feeling the answer is already in the question - “subscribe” - but I have no idea where to start and what to google for.)

[AaronSterling]

Injecting services best practises

private _example: BehaviorSubject<number> = new BehaviorSubject<number>(5); // update example this._example.next(6); // method exposed in provider for pages to use exampleStream(): Observable<number> { return this._example.asObservable(); } // in a page exampleLocalCopy: number; this.exampleProvider.exampleStream().subscribe(ex => this.exampleLocalCopy = ex);

[Audrey84]

@AaronSterling

subscribe

At least I was right with my intuition

Thanks.