Tips for enhancing functionality with dependencies in Angular 2

Question

Tips for enhancing functionality with dependencies in Angular 2

I am working with a ParentService that has dependencies like:

@Injectable()
export class ParentService{
  constructor(private http:Http, private customService:CustomService){}
}

Now, I want to create a ChildService that extends the ParentService:

@Injectable()
export class ChildService extends ParentService{
  constructor (){
    super(??) <= typescript is now prompting me to enter two parameters as per ParentService's constructor
  }
}

Edit-----------------

@Injectable()
export class ParentService{
  constructor(private http:Http, private customService:CustomService){
       get(){this.http.get(...)}
  }
}

@Injectable()
export class ChildService extends ParentService{
  constructor (private http:Http, private customService:CustomService){
    super(http, customService)
  }
}

After setting this up, the components can use it like so:

export class Cmp {
  constructor(private childService:ChildService){
    this.childService.get()
  }
}

angular typescript extends angular2-services

Answer 1

Answer №1

To properly initialize the super class, it is necessary to pass and repeat the parameters in the super call:

@Injectable()
export class ChildService extends ParentService{
  constructor (http:Http, customService:CustomService){
    super(http, customService);
  }
}

There are a few clever techniques to navigate issues like Inheritance and dependency injection

Answer 2

To properly initialize the super class, it is necessary to pass and repeat the parameters in the super call:

@Injectable()
export class ChildService extends ParentService{
  constructor (http:Http, customService:CustomService){
    super(http, customService);
  }
}

There are a few clever techniques to navigate issues like Inheritance and dependency injection

Answer 3

Answer №2

One way to create a base service without using the @Injectable() decorator is by declaring a parent class that contains all the necessary methods and dependencies. This approach allows for flexibility in how the methods are implemented in child classes.

// Define a simple base class without @Injectable()
export abstract class BaseLoginService {
  constructor(
    private http: HttpClient, // Private dependency
    private profileGetter: () => Observable<UserDetails>, // Method to retrieve user profile
    private router: Router
  ) {
    this.profileGetter().subscribe(); // Utilize the method
  }

Child classes can then extend the base class to inherit its functionality:

// Child class annotated with @Injectable() if further extension is needed
@Injectable() 
export class LoginService extends BaseLoginService {

  constructor(
    http: HttpClient, // Argument passed instead of private field
    private profileService: ProfileService,
    router: Router,
    private someOtherService: SomeOtherService // Additional services
  ) {
    super(
      http,
      () => profileService.getUserDetailsMethod(), // Lambda function for method retrieval
      router
    );
    this.someOtherService.doSomething(); // Perform custom initialization
  }

To specify the use of LoginService rather than BaseLoginService in the module's providers section:

providers: [
  LoginService,

You can then inject the LoginService into your component classes:

export class LoginComponent implements OnInit {
  constructor(
    private loginService: LoginService
  ) {
  }

If there is a need to utilize the parent service in certain components, you can provide BaseLoginService using the existing LoginService:

providers: [
  {provide: BaseLoginService, useExisting: LoginService}, // For shared components
  LoginService, // For components needing features from the child class

Answer 4

One way to create a base service without using the @Injectable() decorator is by declaring a parent class that contains all the necessary methods and dependencies. This approach allows for flexibility in how the methods are implemented in child classes.

// Define a simple base class without @Injectable()
export abstract class BaseLoginService {
  constructor(
    private http: HttpClient, // Private dependency
    private profileGetter: () => Observable<UserDetails>, // Method to retrieve user profile
    private router: Router
  ) {
    this.profileGetter().subscribe(); // Utilize the method
  }

Child classes can then extend the base class to inherit its functionality:

// Child class annotated with @Injectable() if further extension is needed
@Injectable() 
export class LoginService extends BaseLoginService {

  constructor(
    http: HttpClient, // Argument passed instead of private field
    private profileService: ProfileService,
    router: Router,
    private someOtherService: SomeOtherService // Additional services
  ) {
    super(
      http,
      () => profileService.getUserDetailsMethod(), // Lambda function for method retrieval
      router
    );
    this.someOtherService.doSomething(); // Perform custom initialization
  }

To specify the use of LoginService rather than BaseLoginService in the module's providers section:

providers: [
  LoginService,

You can then inject the LoginService into your component classes:

export class LoginComponent implements OnInit {
  constructor(
    private loginService: LoginService
  ) {
  }

If there is a need to utilize the parent service in certain components, you can provide BaseLoginService using the existing LoginService:

providers: [
  {provide: BaseLoginService, useExisting: LoginService}, // For shared components
  LoginService, // For components needing features from the child class

Answer 5

Answer №3

By setting the DI services as protected within the abstract class and leaving out the constructor in the subclass, you allow the services to be accessible in the subclass.

Answer 6

By setting the DI services as protected within the abstract class and leaving out the constructor in the subclass, you allow the services to be accessible in the subclass.

Tips for enhancing functionality with dependencies in Angular 2

Answer №1

Answer №2

Answer №3

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