如何使用 angular 2 中的依赖项扩展服务

Question

我有一个父服务，它有一些依赖关系，比如

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

我想延长服务

@Injectable()
export class ChildService extends ParentService{
  constructor (){
    super(??) <= typescript now asking to enter two parameters according to ParentServie's constructor
  }
}

编辑----------------

@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)
  }
}

那我可以在组件中使用吗？

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

Answer 1

super的参数class需要重复传递给super调用：

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

有一些 "hacks" 可以解决，例如

Answer 2

干脆做基服……非@Injectable()！例如，您需要提供一种方法来检索 LoginService 中的用户配置文件。对于LoginService的不同实例，这个方法会有所不同，parent class一定不知道这个方法从哪里来的：它可以是lambda，可以是导出函数，它可以是另一个服务的方法。为此，您可以声明 parent 服务 Parent 服务：

// Don't annotate it with @Injectable() ! It's a simple class.
export abstract class BaseLoginService {
  constructor(
    // This won't be injected automatically, 
    // child class must call super() and provide value for this argument.
    // Note: it's private, can't be accessed outside of BaseLoginService class
    private http: HttpClient,
    // Method used to retrieve user profile
    private profileGetter: () => Observable<UserDetails>, 
    private router: Router
  ) {
    this.profileGetter().subscribe(); // Do something with this method
  }

然后在child中扩展它 class:

// Child class must be annotated with @Injectable(),
// if you don't need to extend it further
@Injectable() 
export class LoginService extends BaseLoginService {

  constructor(
    // Note: no public/private/protected here - "http"
    // will be just an argument
    http: HttpClient, 
    private profileService: ProfileService, // This is the private field of LoginService class
    router: Router,
    // Some service used by LoginService class, parent class BaseLoginService
    // doesn't need to know about SomeOtherService
    private someOtherService: SomeOtherService
  ) {
    super(
      http,
      // Need lambda here to capture profileService instance. If
      // profileService.getUserDetailsMethod doesn't use instance
      // fields or methods, then we can simply write 
      // "profileService.getUserDetailsMethod" (without quotes, obviously).
      () => profileService.getUserDetailsMethod(), 
      router
    );
    this.someOtherService.doSomething(); // Custom initialization code
  }

注意：在模块的 providers 部分指定 LoginService 而不是 parent BaseLoginService：

providers: [
  LoginService,

并在组件 classes:

中使用它

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

如果您需要使用 parent 服务（例如，在只需要 parent 服务 class 的功能的共享组件中），则以这种方式提供 BaseLoginService：

providers: [
  {provide: BaseLoginService, useExisting: LoginService}, // For those components which need functionality from base class only
  LoginService, // Still need this one for those components which need functionality from child class

Answer 3

如果在抽象classprotected中做DI服务，而在subclass中省略构造函数，那么subclass中的服务是可用的.

如何使用 angular 2 中的依赖项扩展服务

how to extend service with dependencies in angular 2

angular

typescript

extends

angular2-services