Angular ngIf表达式更改TerrithasbeenscheckedError
我试图在Angular 6应用程序的导航栏菜单中隐藏登录项。我有一个Angular ngIf表达式更改TerrithasbeenscheckedError,angular,angular-ng-if,angular-changedetection,Angular,Angular Ng If,Angular Changedetection,我试图在Angular 6应用程序的导航栏菜单中隐藏登录项。我有一个AuthService,如下所示: import { Injectable, Inject } from '@angular/core'; import { BehaviorSubject } from 'rxjs'; import { map } from 'rxjs/operators'; import { HttpClient, HttpHeaders } from '@angular/common/http'; impo
AuthService
,如下所示:
import { Injectable, Inject } from '@angular/core';
import { BehaviorSubject } from 'rxjs';
import { map } from 'rxjs/operators';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { JwtHelperService } from '@auth0/angular-jwt';
@Injectable({
providedIn: 'root'
})
export class AuthService {
private url: string;
private loggedIn = new BehaviorSubject<boolean>(false);
isLoggedIn$ = this.loggedIn.asObservable();
constructor(private http: HttpClient, private jwtHelper: JwtHelperService, @Inject('BASE_URL') baseUrl: string) {
this.url = baseUrl + 'api/auth';
this.loggedIn.next(this.isLoggedIn());
}
login(credentials) {
const headers = new HttpHeaders({ 'Content-Type': 'application/json' });
return this.http.post<any>(`${this.url}/login`, JSON.stringify(credentials), { headers: headers }).pipe(
map(response => {
if (response && response.token) {
localStorage.setItem('token', response.token);
this.loggedIn.next(true);
return true;
}
return false;
})
);
}
logout() {
localStorage.removeItem('token');
this.loggedIn.next(false);
}
isLoggedIn() {
return !this.jwtHelper.isTokenExpired();
}
}
下面是html:
<li *ngIf="!isLoggedIn" class="nav-item" [routerLinkActive]="['link-active']">
<a class="nav-link" [routerLink]="['/login']">Login</a>
</li>
但是,当我运行此命令时,会出现以下错误:
错误:ExpressionChangedTerrithasBeenCheckedError:表达式已更改
检查后更改。上一个值:“ngIf:true”。现在的
值:“ngIf:false”
我确实读过这个错误,但我不明白如何解决它。有什么帮助吗?我猜这与您在服务构造函数中设置
loggedIn
初始值的方式有关:this.loggedIn.next(this.isLoggedIn())代码>
尽量只在类中声明变量,并且只在构造函数中使其成为新行为主题()
比如:
private url: string;
private loggedIn: BehaviorSubject<boolean>;
isLoggedIn$: Observable<boolean>;
constructor(private http: HttpClient, private jwtHelper: JwtHelperService, @Inject('BASE_URL') baseUrl: string) {
this.url = baseUrl + 'api/auth';
this.loggedIn = new BehaviourSubject<boolean>(this.isLoggedIn());
this.isLoggedIn$ = this.loggedIn.asObservable()
}
私有url:string;
私人loggedIn:行为主体;
isLoggedIn$:可观察;
构造函数(私有http:HttpClient,私有jwtHelper:JwtHelperService,@Inject('BASE_URL')baseUrl:string){
this.url=baseUrl+'api/auth';
this.loggedIn=新行为主体(this.isLoggedIn());
this.isLoggedIn$=this.loggedIn.asObservable()
}
如果这改变了什么,请告诉我。如果您尝试使用方法而不是属性来返回AuthService上的可观察对象,请告诉我
isLoggedIn: BehaviorSubject<boolean> = new BehaviorSubject(false);
isLoggedIn$() {
return this.isLoggedIn.asObservable();
}
isLoggedIn:BehaviorSubject=newbehaviorsubject(false);
isLoggedIn$(){
返回这个.isLoggedIn.asObservable();
}
您可以使用setTimeout解决此错误
export class NavMenuComponent implements OnInit, OnDestroy {
isExpanded = false;
isLoggedIn: boolean;
authSubscription: Subscription;
constructor(private router: Router, private authService: AuthService) {}
ngOnInit() {
setTimeout(() => {
this.authSubscription = this.authService.isLoggedIn$
.subscribe(loggedIn => this.isLoggedIn = loggedIn);
});
}
ngOnDestroy() {
this.authSubscription.unsubscribe();
}
onLogout() {
this.authService.logout();
this.router.navigate(['/login']);
}
collapse() {
this.isExpanded = false;
}
toggle() {
this.isExpanded = !this.isExpanded;
}
}
不幸的是,html没有发布到帖子中,请更新它。@AlexanderLeonov抱歉!已更新。此错误将仅出现在您的开发环境中。如果在部署代码时启用prod模式,它就会消失。另一方面,如果直接使用异步管道,则不必管理isLoggedIn等状态,angular也将负责取消订阅。因此,您不需要执行此操作。authSubscription.unsubscribe();也没有。这没有帮助。@ataravati有可能在stackblitz中制造此问题吗?
export class NavMenuComponent implements OnInit, OnDestroy {
isExpanded = false;
isLoggedIn: boolean;
authSubscription: Subscription;
constructor(private router: Router, private authService: AuthService) {}
ngOnInit() {
setTimeout(() => {
this.authSubscription = this.authService.isLoggedIn$
.subscribe(loggedIn => this.isLoggedIn = loggedIn);
});
}
ngOnDestroy() {
this.authSubscription.unsubscribe();
}
onLogout() {
this.authService.logout();
this.router.navigate(['/login']);
}
collapse() {
this.isExpanded = false;
}
toggle() {
this.isExpanded = !this.isExpanded;
}
}