可观察 - 多个订阅者

Question

我对 RxJS 和 Observables 非常陌生。我按照本教程进行操作->

https://coryrylan.com/blog/angular-2-observable-data-services

我的问题是，

有：

OnePage：操作并显示答案

服务：保持相同的答案

SecondPage：操作并显示答案

在该链接中，他将数据订阅到组件数据，如下所示

ngOnInit() { todosService.todos$.subscribe(updatedTodos => this.componentTodos = updatedTodos); todosService.loadTodos(); }

这是我的

onPageWillEnter(){
    this.service.answers$.subscribe(updatedAnswers => {
        this.answers = updatedAnswers;
        console.log("we subscribed from questions");
    });
    this.service.load().then((rootobject:RootObject) =>{
        this.rootobject = rootobject;
        this.questions = rootobject.Item.questions;
        this.current_question = this.service.current_question;
        this.pushNextImage(0);
        console.log(this.answers, " Questions page loaded => then");
    });
    console.log(this.answers, " Questions page loaded");
}

一切都很酷。我可以按如下方式更新全局“答案”和本地“答案”。

markQuestion(event){
   this.current_question = this.questions[event.q_number];
   this.current_question_number = event.q_number;
   //Mark the answer in answers
   this.answers[event.q_number-1] = event.val;
   this.service._answersObserver.next(this.answers);
}

在此之后，当我控制台记录“service.answers”时，它也会更新，但是。

在第二页：

onPageWillEnter(){
      this.service.answers$.subscribe(updatedAnswers => {
          this.answers = updatedAnswers;
          console.log("we subscribed from questions");
      });
      //this.service._answersObserver.next(this.service.answers);
      console.log(this.service.answers$);
      console.log(this.service.answers," Page loaded AnswerSheet" , this.answers ," => answer_list");
  }

它甚至没有进入订阅事件。控制台中没有任何内容..除非我这样做：

this.service._answersObserver.next(this.service.answers);

这是为什么呢？

这里是笨蛋https://plnkr.co/edit/c3fu5hsPZXslLegdeD0p?p=info

Answer 1

如果在AnswerSheetPage类的构造函数中添加this.service.answers$.subscribe，而不是在onPageWillEnter方法中，是否有效？