Dependency injection into abstract class typescript(Angular2)

Question

I have abstract class(without constructor) and I want to inject another class into it.

Abstract class:

import { ErrorHandler } from '../../shared/services/errorHandler.service'; import { Inject } from '@angular/core';   export abstract class BaseApiComponent<T> {     @Inject(ErrorHandler) errorHandler: ErrorHandler;      this.errorHandler.test(); } 

Injected class:

import { Injectable } from '@angular/core';  @Injectable() export class ErrorHandler  {   constructor() { }     public test() {     console.log('Test');   }  } 

And I have next error

ORIGINAL EXCEPTION: TypeError: Cannot read property 'test' of undefined 

How i can fix this?

Answer 1

As of Angular 2 RC5 the DI becomes simpler. You don't need to decorate the stuff with @Injectable(). Instead, you just declare it for DI in one place - NgModule.

export class ErrorHandler {     test() {         console.log('ErrorHandler.test()');     } }  export abstract class BaseApiComponent<T> {     // use protected property parameter in abstract class     // for accessibility from descendants.     constructor(protected errorHandler: ErrorHandler) {}      someMethod() {         this.errorHandler.test();     } }  export class ApiComponentImpl<T> extends BaseApiComponent<T> {     // use @Inject decorator     constructor(@Inject(ErrorHandler) errorHandler: ErrorHandler) {         super(errorHandler);     } } 

app.module.ts:

// class declarations @NgModule({     providers: [         ErrorHandler,         ApiComponentImpl     ] }) export class AppModule{ }  // bootstrap the app platformBrowserDynamic().bootstrapModule(AppModule); 

You can employ OpaqueToken to improve modularity and remove type dependency:

export const errorHandlerToken = new OpaqueToken('ErrorHandler'); 

in the module:

    providers: [         // using OpaqueTokens you can change the provided value         // to anything without changing consumer code          {provide: errorHandlerToken, useClass: ErrorHandler}, 

constructor:

    constructor(@Inject(errorHandlerToken) errorHandler: ErrorHandler) { 

Answer 2

Angular DI only supports constructor injection, which means you need a constructor.

You also can't inject into an abstract class directly because an abstract class is not supposed to be instantiatable.

Therefore it has to be like:

export abstract class BaseApiComponent<T> {     constructor(errorHandler: ErrorHandler) {}      someMethod() {      this.errorHandler.test();     } }  export class ApiComponentImpl<T> {     constructor(errorHandler: ErrorHandler) {       super(errorHandler);     }  }