Error: Template parse errors:
Can't bind to 'ngSwitch' since it isn't a known property of 'div'.

import { CommonModule } from '@angular/common';
@NgModule(
 {
  declarations: [ ],
  imports: [
   CommonModule
  ],
  exports: [ ],
  providers: [ ]
 }
)
export class MainModule { }

//login.service.ts
// 这个是登录服务
import { Injectable } from '@angular/core';

@Injectable()
export class LoginService {
 isLoggedIn: boolean = false;
 login(){
  this.isLoggedIn=true;
 }
}

// login.component.ts
//登录界面，只有一个登录按钮，点击后登录会把LoginService中的isLoggedIn变为true

import { Component, OnInit } from '@angular/core';
import { Router } from '@angular/router';
import { LoginService } from '../login/login.service';
@Component({
 selector: 'app-login',
 template:`Login`,
 providers: [LoginService]
})
export class LoginComponent implements OnInit {

 constructor(private router: Router, private loginService: LoginService) { }

 login() {
 this.loginService.login();
 console.log(this.loginService.isLoggedIn); //结果为true
 this.router.navigate(['/main']);
 }
}

// main.component.ts
// 这个是登陆后的主界面

import { Component} from '@angular/core';
import { LoginService } from '../login/login.service';

@Component({
 selector: 'app-main',
 template: `
HOME
`,
 providers: [LoginService]
})
export class MainComponent implements OnInit {

 private userType: string ;
 constructor(private loginService: LoginService) {
 console.log(this.loginService.isLoginIn); //结果为false
 }
}