TypeError: Cannot read property 'UserName' of undefined with Angular 2

Question

我想在我的 angular 2 应用程序中显示当前用户的用户名。后台使用.net core web开发 api.

我写了这段代码，但在控制台中得到了这个错误：

TypeError: Cannot read property 'UserName' of undefined

class 授权服务

import {Injectable, EventEmitter} from "@angular/core";
import {Http, Headers, Response, RequestOptions} from "@angular/http";
import {Observable} from "rxjs/Observable";
import {AuthHttp} from "./auth.http";
import {User} from "./user";

@Injectable()

export class AuthService {
    authKey = "auth";

    constructor(private http: AuthHttp) {
    }

    // Persist auth into localStorage or removes it if a NULL argument is given
    setAuth(auth: any): boolean {
        if (auth) {
            localStorage.setItem(this.authKey, JSON.stringify(auth));
        }
        else {
            localStorage.removeItem(this.authKey);
        }
        return true;
    }

    // Retrieves the auth JSON object (or NULL if none)
    getAuth(): any {
        var i = localStorage.getItem(this.authKey);
        if (i) {
            return JSON.parse(i);
        }
        else {
            return null;
        }
    }

    // Returns TRUE if the user is logged in, FALSE otherwise.

    isLoggedIn(): boolean {
        return localStorage.getItem(this.authKey) != null;
    }

    **get() {
        return this.http.get("api/Accounts")
            .map(response => <User>response.json());
    }**

}

我确定用户已登录，因为我可以读取他的令牌。

网络api方法

 /// <summary>
        /// GET: api/accounts
        /// </summary>
        /// <returns>A Json-serialized object representing the current account.</returns>
        [HttpGet()]
        public IActionResult Get()
        {
            var id = GetCurrentUserId(); 
            //var id = User.FindFirst(ClaimTypes.NameIdentifier).Value;
            var user = DbContext.Users.Where(i => i.Id == id).FirstOrDefault();
            if (user != null) return new JsonResult(new UserViewModel()
            {
                Type = user.Type,
                UserName = user.UserName,
                Email = user.Email,
                DisplayName = user.DisplayName,
                PhoneNumber = user.PhoneNumber,
                DisplayPhoneNumber = user.DisplayPhoneNumber,
                Description = user.Description

            }, DefaultJsonSettings);
            else return NotFound(new { error = String.Format("User ID {0} has not been found", id) });
        }

class 打字稿中的用户

export class User {
    constructor(
        public Type: number,
        public UserName: string,
        public DisplayName: string,
        public PhoneNumber: string,
        public DisplayPhoneNumber: boolean,
        public Description: string,
        public Password: string,
        public PasswordNew: string,
        public Email: string
    ) {
    }
}

angular2

中的组件代码

import {Component, OnInit} from "@angular/core";
import {Router, ActivatedRoute} from "@angular/router";
import {AuthService} from "./auth.service";
import {AuthHttp} from "./auth.http";
import {User} from "./user";

@Component({
    selector: "home",
    templateUrl: "templates/home.component.html",
    //template: `<h1>Home Component</h1>`
})

export class HomeComponent {

    isRegister: boolean;
    currentUser: User;
    constructor(
        public router: Router,
        public authService: AuthService,
        private activatedRoute: ActivatedRoute
    ) {

        //this.isRegister = this.authService.isLoggedIn();
        //console.log(this.isRegister);
    }
    ngOnInit() {
        if (this.authService.isLoggedIn()) {
            this.authService.get().subscribe(
                User => this.currentUser = User
            );           
            console.log(this.isRegister);
            console.log(this.currentUser.UserName);               
        }
    }
}

代码模板html

 <div *ngIf="currentUser"><h1>{{currentUser.UserName}}</h1></div>

我不明白为什么这不起作用。

Answer 1

您正在尝试在 this.authService.get() 解析 User 值之前访问 this.currentUser.UserName，因为 this.authService.get 是异步的，所以这样做：

     ngOnInit() {
        if (this.authService.isLoggedIn()) {
            this.authService.get().subscribe(
                User => {
                  this.currentUser = User
                  console.log(this.isRegister);
                  console.log(this.currentUser.UserName);
            });           

        }
    }

Answer 2

尝试替换：

currentUser: User;

作为

currentUser = new User();

控制台中未定义的错误消失了。

TypeError: Cannot read property 'UserName' of undefined with Angular 2

TypeError: Cannot read property 'UserName' of undefined with Angular 2

.net-core

webapi2

angular