Getting instance of service without constructor injection

Question

I have a @Injectable service defined in bootstrap. I want to get the instance of the service without using constructor injection. I tried using Reflective

Answer 1

Another approach would consist of defining a custom decorator (a CustomInjectable to set the metadata for dependency injection:

export function CustomComponent(annotation: any) {
  return function (target: Function) {

    // DI configuration
    var parentTarget = Object.getPrototypeOf(target.prototype).constructor;
    var parentAnnotations = Reflect.getMetadata('design:paramtypes', parentTarget);

    Reflect.defineMetadata('design:paramtypes', parentAnnotations, target);

    // Component annotations / metadata
    var annotations = Reflect.getOwnMetadata('annotations', target);
    annotations = annotations || [];
    annotations.push(annotation);
    Reflect.defineMetadata('annotations', annotations, target);
  }
}

It will leverage the metadata from the parent constructor instead of its own ones. You can use it on the child class:

@Injectable()
export class SomeService {
  constructor(protected http:Http) {
  }
}

@Component()
export class BaseComponent {
  constructor(private service:SomeService) {
  }
}

@CustomComponent({
  (...)
})
export class TestComponent extends BaseComponent {
  constructor() {
    super(arguments);
  }

  test() {
    console.log('http = '+this.http);
  }
}

See this question for more details:

• Angular2 use imported libs from base class

Answer 2

Yes, ReflectiveInjector.resolveAndCreate() creates a new and unconnected injector instance.

You can inject Angulars Injector instance and get the desired instance from it using

constructor(private injector:Injector) {
  injector.get(MyService);
}

You also can store the Injector in some global variable and than use this injector instance to acquire provided instances for example like explained in https://github.com/angular/angular/issues/4112#issuecomment-153811572

Answer 3

In the updated Angular where ngModules are used, you can create a variable available anywhere in the code:

export let AppInjector: Injector;

export class AppModule {
  constructor(private injector: Injector) {
    AppInjector = this.injector;
  }
}

Now, you can use the AppInjector to find any service in anywhere of your code.

import {AppInjector} from '../app.module';

const myService = AppInjector.get(MyService);

Answer 4

StoreService .ts

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

    @Injectable()
    export class StoreService {
      static isCreating: boolean = false;
      static instance: StoreService ;

      static getInstance() {
        if (StoreService.instance == null) {
          StoreService.isCreating = true;
          StoreService.instance = new StoreService ();
          StoreService.isCreating = false;
        }
        return StoreService.instance;
      }
      constructor() {
        if (!StoreService.isCreating) {
          throw new Error('You can\'t call new in Singleton instances! Call StoreService.getInstance() instead.');
        }
     }

  MyAlertMethod(){
    alert('hi);
    }
  }

component.ts

//call this service directly in component.ts as below:-

 StoreService.getInstance().MyAlertMethod();