src / app / layouts / default / default.component.html：3：1-错误NG8001：“路由器出口”不是已知元素：

如何解决src / app / layouts / default / default.component.html：3：1-错误NG8001：“路由器出口”不是已知元素：

default.module.ts

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';

import { DefaultComponent } from './default.component';
import { DashboardComponent } from 'src/app/modules/dashboard/dashboard.component';
import { RouterModule } from '@angular/router';
import { PostsComponent } from 'src/app/modules/posts/posts.component';
import { SharedModule } from 'src/app/shared/shared.module';

@NgModule({
  declarations: [
    DefaultComponent,DashboardComponent,PostsComponent
  ],imports: [
    CommonModule,RouterModule,SharedModule
  ]
  
})
export class DefaultModule { }

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { LayoutModule } from '@angular/cdk/layout';
import { MatToolbarModule } from '@angular/material/toolbar';
import { MatButtonModule } from '@angular/material/button';
import { MatSidenavModule } from '@angular/material/sidenav';
import { MatIconModule } from '@angular/material/icon';
import { MatListModule } from '@angular/material/list';
import { RouterModule } from '@angular/router';



@NgModule({
  declarations: [
    AppComponent
  ],imports: [
    BrowserModule,AppRoutingModule,BrowserAnimationsModule,LayoutModule,MatToolbarModule,MatButtonModule,MatSidenavModule,MatIconModule,MatListModule,RouterModule
  ],exports: [RouterModule],providers: [],bootstrap: [AppComponent]
})
export class AppModule { }

app-routing.module.ts

import { NgModule,Component } from '@angular/core';
import { Routes,RouterModule } from '@angular/router';
import { DefaultComponent } from './layouts/default/default.component';
import { DashboardComponent } from './modules/dashboard/dashboard.component';
import { PostsComponent } from './modules/posts/posts.component';

const routes: Routes = [{
  path: '',component: DefaultComponent,children: [{
    path: '',component: DashboardComponent
  },{
    path: 'posts',component: PostsComponent
  }]
}];

@NgModule({
  imports: [RouterModule.forRoot(routes)],exports: [RouterModule]
})
export class AppRoutingModule { }

default.component.html

<app-header></app-header>
<app-sidebar></app-sidebar>
<router-outlet></router-outlet>
<app-footer></app-footer>

我遇到以下错误

src / app / layouts / default / default.component.ts：5：16 5 templateUrl：“ ./ default.component.html”， ~~~~~~~~~~~~~~~~~~~~~~~~~~ 组件DefaultComponent的模板中发生错误。 src / app / layouts / default / default.component.html：3：1-错误NG8001：“路由器出口”不是已知元素： 1.如果“ router-outlet”是Angular组件，则请验证它是否是此模块的一部分。 2.如果“路由器出口”是Web组件，则将“ CUSTOM_ELEMENTS_SCHEMA”添加到该组件的“ @ NgModule.schemas”以禁止显示此消息。

3 <router-outlet></router-outlet>
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  src/app/layouts/default/default.component.ts:5:16
    5   templateUrl: './default.component.html',~~~~~~~~~~~~~~~~~~~~~~~~~~
    Error occurs in the template of component DefaultComponent.
src/app/layouts/default/default.component.html:4:1 - error NG8001: 'app-footer' is not a known element:
1. If 'app-footer' is an Angular component,then verify that it is part of this module.
2. If 'app-footer' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

4 <app-footer></app-footer>