我如何从另一个模块导入服务

Question

In my application, I have different modules. I want them to have one common navigation service. But when I call a service in a component of module I get an error.

Can't resolve all parameters for PersonalPage: (?).

What could be the problem?

app.module.ts

import { NavService } from "../shared/nav-service/nav.service";
import { PersonalPageModule } from '../pages/personal/personal.module';

@NgModule({
     ...
     imports: [
         ...
         PersonalPageModule,
         ...
     ],
     providers: [
         ...
         NavService,
         ...
     ]
     ...
});

personal.ts

import { NavService } from "../../shared/nav-service/nav.service";

@IonicPage({
  name: 'page-personal',
  segment: 'personal/:hash' 
})

@Component({
  selector: 'page-personal',
  templateUrl: 'personal.html' 
})

export class PersonalPage implements OnDestroy{
  constructor(private navService: NavService) {
  }
}

nav.service.ts

import { Injectable } from '@angular/core';
import { PersonalPage } from '../../pages/personal/personal';

@Injectable()
export class NavService {}

Answer 1

a service is disponible to all the components that was in a module defined in the module where the service is

@NgModule({
    declarations: [
        AppComponent,  //<--this can access to the service
        MyHeaderComponent    ],  //<--this one too
    imports: [
        ...
        Module2Module,  //<--all the components defined in this module too
        Module3Module,   //<--all the components defined in this module too
        AppRoutingModule,
        DndModule.forRoot()
    ],
    providers: [MyService]
})

if Module2Module import Submodule3, all the component defined in Submodule 3 too. And Module2Module or Module3Module NOT include the service. That's the service are declared as provider in a unique module

You service needn't import any module or component what want to be use it, is the component that want to use the service who must import then and use in the constructor