How to inject service into class (not component)

Question

I'd like 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();   } } 

I tried and it doesn't work. It seems like service need to be used in only component or service.

Is there a way to use a service in a normal class? or it's a bad practice to use a service in a normal class.

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);