Angular 2 - What is a DI error?

Question

I'm having an error when I import a service, but I have no idea why

import { CDService } from "../../services/definition";

constructor(
    private toastyCommunicationService: ToastyCommunicationService,
    private CDService : CDService,
    private SharedService: SharedService,
    private DatePipe: DatePipe
) { }

I have made my service litteraly empty because I was so frustrated with the error and not knowing what was causing it.

export class CDService {

}

Now I receive the error

EXCEPTION: Uncaught (in promise): Error: DI Error
Error: DI Error

I have 2 questions:

1) What the hell is a DI error?

2) How can I solve this error?

Answer 1

It is dependency injection error. I think you are missing @Injectable() decorator:

@Injectable() // this line
export class CDService {

} 

Edit:

Have you added CDService into NgModule?

Answer 2

确保将此服务添加到模块的providers

Answer 3

Make sure your service is injectable by using @Injectable() . This way angular understands its not only a typesscript class but its a angular service.