@Component({
   selector: 'app-home',
   templateUrl: './home.component.html',
   styleUrls: ['./home.component.scss'],
   providers: [ QuestionService ]
 })
 export class HomeComponent implements OnInit {
   constructor(
     private questionService: QuestionService,
     private router: Router
   ) { }

  questions = []
  title = 'old'

  ngOnInit(): void {
    this.getQuestions();
  }

  getQuestions(): void {
    this.questionService.getQuestions()
      .then(questions => this.questions = questions)
      .catch((error) => {
        console.error(error);
    });
 }

对应的模板

{{ title }}

  

  ｛{ question.content }｝
 

理应在页面上显示question.content 但是没有显示。。这是为什么？

但是如果这样写

@Component({
   selector: 'app-home',
   templateUrl: './home.component.html',
   styleUrls: ['./home.component.scss'],
   providers: [ QuestionService ]
 })
 export class HomeComponent implements OnInit {
   constructor(
     private questionService: QuestionService,
     private router: Router
   ) { }

  questions = []
  title = 'old'

  ngOnInit(): void {
    this.getQuestions();
  }

  getQuestions(): void {
    this.questionService.getQuestions()
      .then(questions => this.questions = questions)
      .catch((error) => {
        console.error(error);
    });
    setTimeout(() => {
      this.title = 'new';
    }, 1000);
 }

又正常显示question.content了。这是为什么？