角度从组件中的服务获取字符串值

Question

我正在尝试从QuizService中获取字符串变量的值，以显示在di-quiz组件的模板中，以使用数据绑定进行显示。

在我的quiz.service.ts文件中，我有：

@Injectable({providedIn: 'root'}) {
  export class QuizService {
  explanationText: string;
  ...

  setExplanationAndCorrectAnswerMessages() {
    this.question = this.getQuestion;
    if (this.question) {
      if (this.correctAnswers.length === 1) {
        this.explanation = ' is correct because ' + this.question.explanation + '.';
      }
      if (this.correctAnswers.length > 1) {
        this.explanation = ' are correct because ' + this.question.explanation + '.';
      }
    }

    if (this.correctAnswers && this.correctAnswers.length === 1) {
      const correctAnswersText = this.correctAnswers[0];
      this.explanationText = 'Option ' + correctAnswersText + this.explanation;
      console.log(this.explanationText);
      this.correctAnswerMessage = 'The correct answer is Option ' + this.correctAnswers[0] + '.';
      console.log(this.correctAnswerMessage);
    }
    if (this.correctAnswers && this.correctAnswers.length > 1) {
      if (this.correctAnswers[0] && this.correctAnswers[1]) {
        const correctAnswersText = this.correctAnswers[0] + ' and ' + this.correctAnswers[1];
        this.explanationText = 'Options ' + correctAnswersText + this.explanation;
        console.log(this.explanationText);
        this.correctAnswerMessage = 'The correct answers are Options ' + correctAnswersText + '.';
        console.log(this.correctAnswerMessage);
      }
      ...
    }
  }

在我的[[di-quiz.component.ts中，我有一个getter / setter和构造函数，如下所示：

get explanation(): string { return this.quizService.explanationText; };
set explanation(value: string) { this.quizService.explanationText = value; };

constructor(private quizService: QuizService,
            private timerService: TimerService,
            private route: ActivatedRoute) {
  this.explanationText = this.explanation;
  console.log("ExpTxt: " + this.quizService.explanationText);
}

并且在我的
di-quiz.component.html

中，我有

<section id="question" [class.answered]="answer">
  <span *ngIf="!answer">{{ question?.questionText }}</span>
  <span *ngIf="answer">{{ explanationText }}</span>
</section>

console.log显示的是undefinedText的未定义，并且选择答案后，与模板的数据绑定不显示任何的explorationText的内容。关于为什么这不起作用的任何想法吗？

Answer 1

更改上面的构造函数，

constructor(
  private quizService: QuizService,
  private timerService: TimerService,
  private route: ActivatedRoute
  ) {
     this.explanation = 'Text you want';
     this.explanationText = this.explanation;
     console.log("ExpTxt: " + this.quizService.explanationText);
}