You can use a BehaviorSubject for communicating between different components throughout the app. You can define a data sharing service containing the BehaviorSubject to which you can subscribe and emit changes.
Define a data sharing service
import { Injectable } from '@angular/core';
import { BehaviorSubject } from 'rxjs';
@Injectable()
export class DataSharingService {
public isUserLoggedIn: BehaviorSubject<boolean> = new BehaviorSubject<boolean>(false);
}
Add the DataSharingService in your AppModule providers entry.
Next, import the DataSharingService in your <app-header> and in the component where you perform the sign-in operation. In <app-header> subscribe to the changes to isUserLoggedIn subject:
import { DataSharingService } from './data-sharing.service';
export class AppHeaderComponent {
// Define a variable to use for showing/hiding the Login button
isUserLoggedIn: boolean;
constructor(private dataSharingService: DataSharingService) {
// Subscribe here, this will automatically update
// "isUserLoggedIn" whenever a change to the subject is made.
this.dataSharingService.isUserLoggedIn.subscribe( value => {
this.isUserLoggedIn = value;
});
}
}
In your <app-header> html template, you need to add the *ngIf condition e.g.:
<button *ngIf="!isUserLoggedIn">Login</button>
<button *ngIf="isUserLoggedIn">Sign Out</button>
Finally, you just need to emit the event once the user has logged in e.g:
someMethodThatPerformsUserLogin() {
// Some code
// .....
// After the user has logged in, emit the behavior subject changes.
this.dataSharingService.isUserLoggedIn.next(true);
}