Angular 错误类型错误：无法读取属性'；id'；未定义的

我遇到一个错误TypeError：当我导航到我的组件时，无法读取未定义的属性“id”。调试完代码后，我发现错误在哪里，但我没有找到合适的方法来解决它。也许你能帮我

下面是my.ts文件：

@Component({
  selector: 'app-forum-thread',
  templateUrl: './forum-thread.component.html',
  styleUrls: ['./forum-thread.component.css']
})
export class ForumThreadComponent implements OnInit {
  @Input() theme: Theme;
  threads: Observable<Thread[]>;

constructor(
  private route: ActivatedRoute,
  private location: Location,
  private themeService: ThemeService,
  private threadService: ThreadService
) { }

ngOnInit() {
  this.getTheme();
  this.getThreads();
}

getTheme(): void {
  this.themeService.getTheme(this.route.snapshot.paramMap.get('theme'))
    .subscribe(theme => this.theme = theme);
}

// Error caused by this method..
getThreads(): void {
  this.threads = this.threadService.getThreads(this.theme.id);
}

---

提前感谢您的帮助

在

ngOnInit

块中，您正在异步运行两个函数，因此

getThreads

中的

theme

查找将是未定义的。您需要等待主题设置完成

getTheme(): void {
  this.themeService.getTheme(this.route.snapshot.paramMap.get('theme'))
    .subscribe(theme => {
      this.theme = theme;
      this.getThreads(theme.id);
    });
}

并将

getThreads

更改为：

getThreads(themeId): void {
  this.threads = this.threadService.getThreads(themeId);
}

---

我终于改变了我的代码，把

这个.route.snapshot.paramMap.get（'theme'）常量中的code>，如下所示：

ngOnInit() {
  const id = this.route.snapshot.paramMap.get('theme');

  this.themeService.getTheme(id)
    .subscribe(theme => {
      this.theme = theme,
      this.getThreadsTheme(theme._id)
    });
}

我更改了
gethreads（）
以获取subscribe-in参数的主题，并且没有得到错误类型ERROR：无法再读取未定义消息的属性“id”，但我得到了这个get 500（内部服务器错误）。似乎在调用函数之前没有完成定义。我更新了答案，将线程id作为param接受，而不是在类上查找。
getThreads(themeId): void {
  this.threads = this.threadService.getThreads(themeId);
}

ngOnInit() {
  const id = this.route.snapshot.paramMap.get('theme');

  this.themeService.getTheme(id)
    .subscribe(theme => {
      this.theme = theme,
      this.getThreadsTheme(theme._id)
    });
}