Angular 2 error throw "'router-outlet' is not a known element:". if I use submodule.Please guide

Question

I am learning angular 2. I am facing an error 'router-outlet' is not a known element'. I have one folder dashboard including dashboard.component.ts,dashboard.module.ts,dashboard.component.html. And codes of those files are followings.

    dashboard.module.ts
------------------------------
    import { NgModule }      from '@angular/core';
    import { CommonModule } from '@angular/common';
    import { DashboardComponent }  from './dashboard.component';
    import { AllBookListComponent }  from './allbooklist.component';
    @NgModule({
    imports: [CommonModule],
    declarations: [AllBookListComponent,DashboardComponent],
    exports: [AllBookListComponent,DashboardComponent],
    providers: [],
    })
    export class DashboardModule {
    }

    dashboard.component.ts
-----------------------------
    import { Component } from '@angular/core';
    @Component({
    templateUrl: './dashboard.component.html',
    })
    export class DashboardComponent  
    { 
    }
    dashboard.component.html
------------------------------------
    <a routerLink="aaa" routerLinkActive="active">Home</a>
    <router-outlet ></router-outlet>

    app.module.ts
----------------------------
    import { NgModule }      from '@angular/core';
    import { BrowserModule } from '@angular/platform-browser';
    import { LoginModule }  from './login/login.module';
    import { DashboardModule }  from './dashboard/dashboard.module';
    import { routing } from './app.routing';
    import { AppComponent }  from './app.component';
    @NgModule({
    imports:[ BrowserModule,routing,LoginModule,DashboardModule],
    declarations: [ AppComponent],
    providers: [],
    bootstrap:    [ AppComponent ]
    })
    export class AppModule { }

    app.routing.ts
-----------------------
    import { NgModule } from '@angular/core';
    import { Routes, RouterModule } from '@angular/router';
    import { LoginComponent }  from './login/login.component';
    import { DashboardComponent }  from './dashboard/dashboard.component';
    import { AllBookListComponent }  from './dashboard
    export const routing = RouterModule.forRoot([
    {path: '', component: LoginComponent},
    { path: 'dashboard', component: DashboardComponent,
    children: [
    { path: 'aaa', component: AllBookListComponent }
    ]
    }
    ]);


app.component.ts
-------------------
import { Component } from '@angular/core';
@Component({
  selector: 'my-app',
  template: `<router-outlet></router-outlet>`,
})
export class AppComponent  { name = 'Angular'; }

But if I import the DashboardComponent (import { DashboardComponent } from './dashboard.component';) in app.module.ts instead of dashboard.module.ts then its working fine. My question is why should I import DashboardComponent in app.module.ts instead of dashboard.module.ts?as at last dashboard.module.ts is imported in app.module.ts.Please help

Answer 1

Import RouterModule in DashBoardMoule

explanation

<router-outlet> is a part of RouterModule and your component is trying to access router-outlet and module that contains DashBoardComponent is not importing RouterModule