How to detect changes in Angular 2 using a separate service

Question

How to detect changes in Angular 2 using a separate service

Within my AuthService, I store real-time user data and a method for logging in. When the 'Login' button is clicked, the AuthService is called to retrieve updated user data from the server and update the value of 'this.user'.

As a result, the username is displayed in the header.

Now, the question arises: how can my HeaderComponent be notified when the 'this.user' value in the AuthService has been modified?

javascript angular typescript rxjs

Answer 1

Answer №1

If you want to incorporate an Observable in your AuthService, you can do so by exposing it as a stream that can be subscribed to in your HeaderComponent. A useful approach is to utilize the EventEmitter class, which is an extension of the RxJS Subject class. Additionally, employing a TypeScript setter can automatically trigger events for any changes made. Your implementation may resemble the following:

@Injectable()
export class AuthService {
    private _user: any;
    userStream: EventEmitter<any>;

    constructor() {
      this.userStream = new EventEmitter();
    }

    //code ...

    getUserData() {
        //invoke our setter function
        this.user = newData;
    }

    set user(newValue) {
        this._user = newValue;
        //update user data and emit a value through the userStream
        this.userStream.emit(newValue);
    }
}

You can then integrate your service into your component like so:

@Component({...})
export class HeaderComponent {
    currentUser: any;

    constructor(private authService: AuthService) {
        //subscribe to the stream to receive notifications when user data changes
        authService.userStream.subscribe((newUser) => { this.currentUser = newUser; });
    }
}

This setup allows you to monitor changes within your user data effectively.

Answer 2

If you want to incorporate an Observable in your AuthService, you can do so by exposing it as a stream that can be subscribed to in your HeaderComponent. A useful approach is to utilize the EventEmitter class, which is an extension of the RxJS Subject class. Additionally, employing a TypeScript setter can automatically trigger events for any changes made. Your implementation may resemble the following:

@Injectable()
export class AuthService {
    private _user: any;
    userStream: EventEmitter<any>;

    constructor() {
      this.userStream = new EventEmitter();
    }

    //code ...

    getUserData() {
        //invoke our setter function
        this.user = newData;
    }

    set user(newValue) {
        this._user = newValue;
        //update user data and emit a value through the userStream
        this.userStream.emit(newValue);
    }
}

You can then integrate your service into your component like so:

@Component({...})
export class HeaderComponent {
    currentUser: any;

    constructor(private authService: AuthService) {
        //subscribe to the stream to receive notifications when user data changes
        authService.userStream.subscribe((newUser) => { this.currentUser = newUser; });
    }
}

This setup allows you to monitor changes within your user data effectively.

How to detect changes in Angular 2 using a separate service

Answer №1

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