Top method for transferring information from a service to a dynamic format in Angular5

Question

Top method for transferring information from a service to a dynamic format in Angular5

Looking for the most efficient method to populate a form with data from a service in Angular 5. My goal is to keep component code to a minimum and have the variable-data stored within services rather than components.

The content is loaded through a secondary service by the main service.

Sample Service:

@Injectable()
    export class UserService {
    
    private user: User;
    
    private url: string = 'v1/user';
    
    constructor(
        private restService: RestService
    
    ) {
        this.restService.get(this.url).subscribe(
            res => {
                this.user = res;
            }
        );
    
    }
    
    public getUser(): User {
        return this.user;
    }

Sample Component:

export class UserComponent implements OnInit {
    
    private form: FormGroup;
    
    constructor(
        private userService: UserService
    ) {}
    
    ngOnInit(): void {
        // Initialize an empty form
        this.form = new FormGroup({
                email: new FormControl()
            })
        );
    
        // Populate the form with values from the service
        this.form.patchValue(this.userService.getUser());
    }

If I introduce a delay (like 10 seconds using setTimeout) before executing patchValue(), everything works fine, but that's clearly not ideal.

Is there a way to determine when the service code has been fully loaded, without resorting to using Observables?

I appreciate any suggestions or insights!

angular typescript angular-reactive-forms

Answer 1

Answer №1

To handle subscriptions in a more efficient way, you have two options. You can either subscribe inside the component directly or create a subject that emits values once processing is complete.

Subscription within the component:

@Injectable()
export class UserService {

private user: User;
private url: string = 'v1/user';

constructor(private restService: RestService) {}

public getUser() {
    return this.restService.get(this.url);
}

In your component.ts file:

export class UserComponent implements OnInit {

private form: FormGroup;
userSub: Subscription;
user: string;

constructor(
private userService: UserService
) {}

ngOnInit(): void {
    this.userSub = this.userService.getUser()
     .subscribe((res) => { 
         this.user = res;
         // Initialize the empty form
         this.form = new FormGroup({
            'email': new FormControl(this.user, [])
        });
     });

}

Subscribing to a subject in the service:

@Injectable()
export class UserService {
userRetrieved: new Subject<User>();
private user: User;
private url: string = 'v1/user';

constructor(
private restService: RestService
) {
    this.restService.get(this.url).subscribe((res) => {
        this.user = res;
        this.userRetrieved.next(this.user);
    });

}

public getUser(): User {
    return this.user;
}

Then, in your component, subscribe to it:

export class UserComponent implements OnInit {
userSub: Subscription;
private form: FormGroup;

constructor(
private userService: UserService
) {}

ngOnInit(): void {
    // Initialize the empty form
    this.form = new FormGroup({
        email: new FormControl()
    });
    
    this.userSub = this.userService.userChanged
       .subscribe((res: User) => { 
        // Code to update and fill the form with values from the service
        // this.form.patchValue(res);
       });

}

Answer 2

To handle subscriptions in a more efficient way, you have two options. You can either subscribe inside the component directly or create a subject that emits values once processing is complete.

Subscription within the component:

@Injectable()
export class UserService {

private user: User;
private url: string = 'v1/user';

constructor(private restService: RestService) {}

public getUser() {
    return this.restService.get(this.url);
}

In your component.ts file:

export class UserComponent implements OnInit {

private form: FormGroup;
userSub: Subscription;
user: string;

constructor(
private userService: UserService
) {}

ngOnInit(): void {
    this.userSub = this.userService.getUser()
     .subscribe((res) => { 
         this.user = res;
         // Initialize the empty form
         this.form = new FormGroup({
            'email': new FormControl(this.user, [])
        });
     });

}

Subscribing to a subject in the service:

@Injectable()
export class UserService {
userRetrieved: new Subject<User>();
private user: User;
private url: string = 'v1/user';

constructor(
private restService: RestService
) {
    this.restService.get(this.url).subscribe((res) => {
        this.user = res;
        this.userRetrieved.next(this.user);
    });

}

public getUser(): User {
    return this.user;
}

Then, in your component, subscribe to it:

export class UserComponent implements OnInit {
userSub: Subscription;
private form: FormGroup;

constructor(
private userService: UserService
) {}

ngOnInit(): void {
    // Initialize the empty form
    this.form = new FormGroup({
        email: new FormControl()
    });
    
    this.userSub = this.userService.userChanged
       .subscribe((res: User) => { 
        // Code to update and fill the form with values from the service
        // this.form.patchValue(res);
       });

}

Answer 3

Answer №2

A creative solution is to configure your service as a resolver in order to achieve your desired outcome.

@Injectable()
export class UserService implements Resolve<any> {

    private user: User;

    private url: string = 'v1/user';

    constructor(
        private restService: RestService
    ) {}

    public resolve(route: ActivatedRouteSnapshot): Observable<any> {
        return this.restService.get(this.url).map(
            user => {
                this.user = user;    
            },
            error => {}
        ).first();
    }

}

Then, simply add the service to your router similar to how you would for a typical resolver.

const routes: Routes = [
    {
        path: 'user',
        component: UserComponent,
        resolve: {
            user: UserService
        }
    }
]

@NgModule({ 
  imports: [ RouterModule.forRoot(routes)],
    exports: [RouterModule],
    providers: [UserService] 
})

This approach ensures that the service data is refreshed seamlessly whenever you navigate within your application.

I trust this information proves beneficial to you.

Answer 4

A creative solution is to configure your service as a resolver in order to achieve your desired outcome.

@Injectable()
export class UserService implements Resolve<any> {

    private user: User;

    private url: string = 'v1/user';

    constructor(
        private restService: RestService
    ) {}

    public resolve(route: ActivatedRouteSnapshot): Observable<any> {
        return this.restService.get(this.url).map(
            user => {
                this.user = user;    
            },
            error => {}
        ).first();
    }

}

Then, simply add the service to your router similar to how you would for a typical resolver.

const routes: Routes = [
    {
        path: 'user',
        component: UserComponent,
        resolve: {
            user: UserService
        }
    }
]

@NgModule({ 
  imports: [ RouterModule.forRoot(routes)],
    exports: [RouterModule],
    providers: [UserService] 
})

This approach ensures that the service data is refreshed seamlessly whenever you navigate within your application.

I trust this information proves beneficial to you.

Top method for transferring information from a service to a dynamic format in Angular5

Answer №1

Answer №2

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