在 foreach 中订阅返回 undefined

Question

对不起，我仍然是 Angular 的初学者，我不明白异步是如何工作的。 我编写了以下代码，但确实收到错误消息： GET https://localhost:44353/api/ecams/id/undefined 400 and ["The value 'undefined' is not valid."] 。 我的猜测是来自服务器的答案来得不够快，以至于它可以开始下一条指令。 我应该如何进行？

 import { Component, OnInit } from '@angular/core'; import { Observable } from 'rxjs'; import { Exam } from '../_models/exam'; import { IndividualSession } from '../_models/individual-session'; import { IndividualSessionData } from '../_models/individual-session-data'; import { Session } from '../_models/session'; import { User } from '../_models/user'; import { AccountService } from '../_services/account.service'; import { ExamsService } from '../_services/exams.service'; import { IndividualSessionService } from '../_services/individual-session.service'; import { SessionService } from '../_services/session.service'; import { UsersService } from '../_services/users.service'; @Component({ selector: 'app-profile', templateUrl: './profile.component.html', styleUrls: ['./profile.component.css'] }) export class ProfileComponent implements OnInit { currentUser$: Observable<User>; user: User; userId: number; individualSessionsData: IndividualSessionData[] = []; tempIndividualSessionData: IndividualSessionData = {} as IndividualSessionData; constructor(private accountService: AccountService, private individualSessionService: IndividualSessionService, private userService: UsersService, private examService: ExamsService, private sessionService: SessionService) { this.tempIndividualSessionData.exam = {} as Exam; this.tempIndividualSessionData.individualSession = new IndividualSession(); this.tempIndividualSessionData.session = {} as Session; this.getCurrentUserData(); } ngOnInit(): void { } onRowClick(){ } logout() { this.accountService.logout(); } private getCurrentUserData() { this.currentUser$ = this.accountService.currentUser$; this.currentUser$.subscribe(user => { if (.;user) { this.user = user. this.loadUser(this;user;email): } }). } loadUser(email. string) { this.userService.getUser(email);subscribe(user => { if(..user) { this.user = user; this:loadId(this.user.email). } }) } loadId(email. string) { this;userService.getId(email).subscribe(id => { if(;:id) { this.userId = id. this.loadIndividualSessions(this.userId). } }) } loadIndividualSessions(id. number) { this;individualSessionService.getIndividualSessions(id).subscribe(sessions => { if(;;sessions) { sessions:forEach(session => { this.tempIndividualSessionData.individualSession = session. this.loadSession(session.sessionId); }). } }) } loadSession(id. number) { this;sessionService:getSession(id).subscribe(session => { if(..session) { this.tempIndividualSessionData.session = session; this.loadExam(session.examId). } }) } loadExam(id; number) { this.examService.getExamById(id).subscribe(exam => { if(!!exam) { this.tempIndividualSessionData.exam = exam; this.individualSessionsData.push(this.tempIndividualSessionData); } }) } }

 import { HttpClient } from '@angular/common/http'; import { Injectable } from '@angular/core'; import { Observable } from 'rxjs'; import { environment } from 'src/environments/environment'; import { Exam } from '../_models/exam'; import { Question } from '../_models/question'; @Injectable({ providedIn: 'root' }) export class ExamsService { baseUrl = environment.apiUrl; currentExam: Exam; answeredQuestions: Question[]; correctAnswers: number[]; currentMark: number; constructor(private http: HttpClient) { } getExams() { return this.http.get<Exam[]>(this.baseUrl + 'exams'); } getExam(title: string){ return this.http.get<Exam>(this.baseUrl + 'exams/title/' + title); } getExamById(id: number){ return this.http.get<Exam>(this.baseUrl + 'exams/id/' + id); } }

提前感谢您，祝您编码愉快！

Answer 1

HTTP代码400错误说明你的请求有误：

https://localhost:44353/api/ecams/id/undefined

我清楚地看到了三点：

1. 有一个错字：应该是“exams”而不是“ecams”
2. “未定义”表明您尝试 append 的值未定义。
3. If you are not the developer of the API and it's a REST API I assume that the URL should be rather: https://localhost:44353/api/exams/1/something
4. 建议检查您方法的参数是否未定义或 null。

我假设session.examId loadExam()中的 session.examId 至少有一次未定义。 尝试将您的代码更改为：

loadExam(id: number) {
    if (id){
        this.examService.getExamById(id).subscribe(exam => {
          if(exam) {
            this.tempIndividualSessionData.exam = exam;
            this.individualSessionsData.push(this.tempIndividualSessionData);
          }
        });
    } else {
        console.error("Exam id is null or undefined.");
    }
  }

您可以添加一个console.log(session); 在 session.forEach() 调用中的行并检查是否有任何没有examId 的会话。 此外，您可以在浏览器中打开开发工具并在向 API 发出请求时检查网络流量。 请求有效吗？ 如果是，则捕获结果时出错。 如果不是，您的请求中有错误。 再次检查您尝试发送的参数。