Passing parameters to constructor of a service using Dependency Injection?

Question

I have custom service class:

@Injectable()

export class CustomService {
  constructor(num: number) {
  }
}

This class is injected in constructor of component like this:

constructor(private cs: CustomService) {
}

But how to pass parameter num to service in constructor described above? Something like that:

constructor(private cs: CustomService(1)) {
}

I know as solution I can use Fabric pattern, but is there only one way to do that?

Off topic, but why do you want to create a stateful service? Services should be stateless and should know nothing about their clients — Trash Can, Jul 27 '17 at 17:06
Otherwise how to pass parameters(settings) to service? Service must work with some incoming data is not it? — Daniel, Jul 27 '17 at 17:11
You can't. Consider providing the example that explains what's your case. Yes, it will likely be a variation of factory. — Estus Flask, Jul 27 '17 at 17:21
Then how to use services right? Is it just set of functions? Does it mean that service can not have constructor? How to put any data in Service then? — Daniel, Jul 27 '17 at 17:23
@Daniel you would generally configure the service at the module level, with `useFactory`, not where it's injected. Read https://angular.io/guide/dependency-injection. — jonrsharpe, Jul 27 '17 at 17:25

score 1 · Accepted Answer · answered Jul 27 '17 at 18:48

1

If CustomService instances should not be injector singletons, it is:

providers: [{ provide: CustomService, useValue: CustomService }]

...

private cs;

constructor(@Inject(CustomService) private CustomService: typeof CustomService) {
  this.cs = new CustomService(1);
}

If CustomService is supposed be memoized to return singletons for respective parameter, instances should be retrieved through additional cache service:

class CustomServiceStorage {
  private storage = new Map();

  constructor(@Inject(CustomService) private CustomService: typeof CustomService) {}
  get(num) {
    if (!this.storage.has(num))
      this.storage.set(num, new this.CustomService(num));

    return this.storage.get(num);
  }
}

answered Jul 27 '17 at 18:48

Estus Flask

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Where to write this `providers: [{ provide: CustomService, useValue: CustomService }]`? What does it mean? – Daniel Jul 27 '17 at 18:55
It depends on your case. In NgModule or Component. See [the manual](https://angular.io/guide/dependency-injection#injector-providers). `useValue` means that CustomService will be injected as a class and won't be instantiated by injector. – Estus Flask Jul 27 '17 at 19:01
You can check [the answer](https://stackoverflow.com/a/44301253/3731501) that uses the same recipe for example. – Estus Flask Jul 27 '17 at 19:03

score 0 · Answer 2 · answered Jul 27 '17 at 17:29

A service can hold data. You could define a public property in your service and set that data.

Here is an example:

import { Injectable } from '@angular/core';

@Injectable() 
export class DataService {
  serviceData: string; 
}

But if you are configuring the service, Jon's comment to your question may be a better solution.

Passing parameters to constructor of a service using Dependency Injection?

2 Answers2

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