根据 ngIf 条件更改 Angular 中 NavBar 的内容

Question

我是 Angular 和 Node JS 的初学者。我正在尝试根据 ngIf 条件更改简单的导航栏。但是，它似乎不起作用。

我已经尝试过使用静态成员变量。

另外，尝试创建一个方法来更改navbar.component 中isUserAuthenticated 的值，并调用homepage.component 和dashboard.component 中的方法。

我也完成了console.log() 并检查了isUserAuthenticated 变量的值。它正在homepage.component 和dashboard.component 上进行更新。但是，NavBar 始终保持不变。

我已经直接在 navbar.component 中更改了值，然后它就可以工作了。所以，我想知道为什么如果我更改其他组件的值它不起作用。

navbar.component.html

       <div *ngIf="!isUserAuthenticated">
          <li class="nav-item">
            <a class="nav-link" href="/"> EX FALSE </a>
          </li>
        </div>

        <div *ngIf="isUserAuthenticated">
          <li class="nav-item">
            <a class="nav-link" href="/"> EX TRUE </a>
          </li>
        </div>

navbar.component.ts

import { Component, OnInit } from '@angular/core';

@Component({
  selector: 'app-navbar',
  templateUrl: './navbar.component.html',
  styleUrls: ['./navbar.component.css']
})
export class NavbarComponent implements OnInit {

  isUserAuthenticated = true;

  constructor() { }

  ngOnInit() { }

  public authenticate() {
    this.isUserAuthenticated = false;
    return  this.isUserAuthenticated;
  }
  public deauthenticate() {
    this.isUserAuthenticated = true;
    return  this.isUserAuthenticated;
  }
}

homepage.component.ts

import { Component, OnInit } from '@angular/core';
import { NavbarComponent } from '../navbar/navbar.component';


@Component({
  selector: 'app-homepage',
  templateUrl: './homepage.component.html',
  styleUrls: ['./homepage.component.css']
})
export class HomepageComponent implements OnInit {

  constructor( ) {

  }

  ngOnInit() {

    console.log("here");
    this.deauthenticate();


  }

  public deauthenticate()
  {
    const comp2 = new NavbarComponent();
    comp2.deauthenticate();
    console.log(comp2.deauthenticate());
  }
}

dashboard.component.ts

import { Component, OnInit } from '@angular/core';
import { NavbarComponent } from '../navbar/navbar.component';



@Component({
  selector: 'app-dashboard',
  templateUrl: './dashboard.component.html',
  styleUrls: ['./dashboard.component.css']
})
export class DashboardComponent implements OnInit {

  constructor( ) {
  }

  ngOnInit() {

    this.authenticate();
  }

  public authenticate()
  {
    const comp2 = new NavbarComponent();
    comp2.authenticate();
    console.log(comp2.authenticate());
  }

}

我希望dashboard 组件在导航栏中显示“EX TRUE”，而homepage 组件在导航栏中显示“EX FALSE”。

Answer 1

正如评论中提到的，您需要创建身份验证服务check this for full example

@Injectable()
export class AuthenticationService {
  authenticated$: BehaviorSubject<boolean> = new BehaviorSubject(false);

  public authenticate() {
    this.authenticated$.next(true);
  }

  public deauthenticate() {
    this.authenticated$.next(false);
  }
}

您以这种方式注入它以便能够在模板中使用它

import { Component } from '@angular/core';

import { AuthenticationService } from '../authentication/authentication.service';

@Component({
  selector: 'my-navbar',
  templateUrl: './navbar.component.html',
  styleUrls: [ './navbar.component.css' ]
})
export class NavbarComponent {
  constructor(
    public authenticationService: AuthenticationService,
  ) {
  }
}

然后在模板中你可以这样做

Authenticated {{ authenticationService.authenticated$ | async }}

<div *ngIf="(authenticationService.authenticated$ | async) === true">
  <li class="nav-item">
    <a class="nav-link" href="/">EX TRUE</a>
  </li>
</div>

<div *ngIf="(authenticationService.authenticated$ | async) === false">
  <li class="nav-item">
    <a class="nav-link" href="/">EX FALSE</a>
  </li>
</div>

<button (click)="authenticationService.authenticate()">Authenticate</button>
<button (click)="authenticationService.deauthenticate()">Deauthenticate</button>

虽然我建议在这种情况下使用 ngSwitch：

<div>
  <li class="nav-item" [ngSwitch]="authenticationService.authenticated$ | async">
    <a class="nav-link" href="/" *ngSwitchCase="true">EX TRUE</a>
    <a class="nav-link" href="/" *ngSwitchDefault>EX FALSE</a>
  </li>
</div>

此外，如果您想为网站的某些部分设置单独的状态，您可以这样做：

@Component({
  selector: 'my-homepage',
  templateUrl: './homepage.component.html',
  styleUrls: [ './homepage.component.css' ],
  // this way you have a separate instance of AuthenticationService here anything that will use this service and is rendered under this component will use a localized version of this service
  providers: [AuthenticationService],
})
export class HomepageComponent {
  constructor(
    public authenticationService: AuthenticationService,
  ) {
  }
}

Answer 2

事情不是这样设计的。对于这种情况，您需要创建一个Service，例如AuthService，它将在两个组件之间共享。

AuthEventSvc

export class AuthEventSvc{

   private authEvent = new BehaviorSubject<boolean>(true);
   constructor(){}

   emitAuthStatus(state: boolean){
     this.authEvent.next(state);
   }

   authListener(){
     return this.authEvent.asObservable();
   }

}

然后从 HomeComponent

发出

export class HomepageComponent implements OnInit {

  constructor(private authEvent: AuthEventSvc ) {

  }

  ngOnInit() {
    this.authEvent.emitAuthStatus(false);
  }
}

并在 NavBarComponent

中订阅它

export class NavbarComponent implements OnInit {

  isUserAuthenticated = true;
  authSubscription : Subscription;

  constructor(private authEvent: AuthEventSvc) { }

  ngOnInit() { 
    this.authSubscription = this.authEvent.authListener().subscribe(state => {
      this.isUserAuthenticated = state;
    })
  }

  ngOnDestroy(){
    this.authSubscription.unsubscribe(); // make sure to unsubscribe
  }

}

您还应该阅读有关 how change detection works 以及如何在 Angular 中使用 NgZone 以获得更清晰的信息，因为这些主题需要长篇文章来解释。我只是给你一些面包屑来帮助你更好地理解:)