angular - How to inject service into class (not component)

Question

I want to inject a service into a class that is not a component.

For example:

Myservice

import {Injectable} from '@angular/core';
@Injectable()
export class myService {
  dosomething() {
    // implementation
  }
}

MyClass

import { myService } from './myService'
export class MyClass {
  constructor(private myservice:myService) {

  }
  test() {
     this.myservice.dosomething();
  }
}

This solution doesn't work (I think because MyClass hasn't been instantiated yet).

Is there another way to use a service in a class (not component)? Or would you consider my code design as inappropriate (to use a service in a class which is not a component)?

Thank you.

Answer 1

Injections only works with classes that are instantiated by Angulars dependency injection (DI).

1. You need to
   • add @Injectable() to MyClass and
   • provide MyClass like providers: [MyClass] in a component or NgModule.

When you then inject MyClass somewhere, a MyService instance gets passed to MyClass when it is instantiated by DI (before it is injected the first time).

2. An alternative approach is to configure a custom injector like

constructor(private injector:Injector) { 
  let resolvedProviders = ReflectiveInjector.resolve([MyClass]);
  let childInjector = ReflectiveInjector.fromResolvedProviders(resolvedProviders, this.injector);

  let myClass : MyClass = childInjector.get(MyClass);
}

This way myClass will be a MyClass instance, instantiated by Angulars DI, and myService will be injected to MyClass when instantiated.
See also Getting dependency from Injector manually inside a directive

3. Yet another way is to create the instance yourself:

constructor(ms:myService)
let myClass = new MyClass(ms);