Angular 4: Inject service having @angular/http as dependency in non-component class

Question

Hi I'm newbie for Angular 4. I'm having one service named 'httpService' which is having @angular/http as one of dependency, there are others as well, which does error handling.

Now i'm having normal class (other than component) say 'Child.ts' which extends base class 'Base.ts' with constructor which sets some properties on class and uses above mentioned httpService to fetch data from server via rest apis.

My Overall structure looks like below.

Base.ts
============================================================
export class Base {
  public url: string;
  public httpSvc: HttpService;

  constructor(url) {
    this.url = url;
  }

  public getUrl(): string {
    return this.url;
  }

  public query(reqParams: URLSearchParams): Observable<any> {
    return this.httpSvc.get(this.getUrl(), reqParams);
  }
}

And having class which extends base class.

Child.ts
============================================================
export class Child extends Base {
  first_name: string;
  last_name: string;
  email: string;

  constructor(url: string) {
    super(url);
  }

  getCurrentUser(): Observable<User> {
    return this.httpSvc.get(this.url + 'get-user-profile');
  }
}

This way i'm having each model with its own method to fetch data from server.

Now in such situation how can i use httpService as its not initialized yet.

Please suggest me the way or better solution.

Thanks

Satish Lakhani

Well, add the http service to the constructor arguments, and construct those obects from an angular component or service where httpSvc is injected. — JB Nizet, Sep 19 '17 at 11:16

score 0 · Answer 1 · answered Sep 19 '17 at 11:17

0

You need to inject it like this:

constructor(private http: HttpService)

remember to provide at a top level, like you app.module:

providers:[
 HttpService
],

answered Sep 19 '17 at 11:17

kodeaben

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Thanks for the reply, but while instantiating child class with url, i don't want to pass httpService instance, so in this case how it will work? – Satish Lakhani Sep 19 '17 at 11:21
@SatishLakhani it won't. An object can't use another object without having a reference to that other object. – JB Nizet Sep 19 '17 at 11:25
@SatishLakhani do you mean like calling a static method? – eko Sep 19 '17 at 11:27
@JBNizet, so is there any other way to achieve the same behaviour i'm asking? – Satish Lakhani Sep 19 '17 at 11:33
I answered in the comment on your question. – JB Nizet Sep 19 '17 at 11:34
you can find your answer here: https://stackoverflow.com/questions/37482460/getting-instance-of-service-without-constructor-injection and here : https://stackoverflow.com/questions/39101865/angular-2-inject-dependency-outside-constructor – MohammadJavad Seyyedi Sep 19 '17 at 11:34

Angular 4: Inject service having @angular/http as dependency in non-component class

1 Answers1