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比较多个行为子对象的最新值

behaviorsubject angular2-observables rxjs5 rxjs

Alexander Mills · 技术社区 · 7 年前

假设我有这个:

  isMatchedCountLessThanTotalCountMessage(){
       // I want to implement this
       // "returns" a string asynchronously
  }

  getMatchedEventsCount() {
    return this.dcs.matchCount.asObservable();
  }

  getTotalEventsCount() {
    return this.dcs.totalCount.asObservable();
  }

matchedCount和totalCount如下:

  public matchCount = new BehaviorSubject<number>(0);
  public totalCount = new BehaviorSubject<number>(0);

当值发生变化时,这些可观察到的值会触发整数。无论何时从其中一个触发一个值,我都想比较两个最近的值,我该怎么做?

我要做的是从方法中返回一个布尔值

因此我可以在HTML中显示:

 <div>{{(isMatchedCountLessThanTotalCountMessage() | async)}}</div>

我认为可以观察到。zip可能会做到:

isMatchedCountLessThanTotalCountMessage(){
    return Observable.zip(
      this.getMatchedEventsCount(),
      this.getTotalEventsCount()
    )
    .subscribe(function(v){
      const intA = v[0];
      const intB = v[1];

        if(intA > intB)
         // but I don't know how to send a message the HTML from here
    });
  }

2 回复 | 直到 6 年前

CozyAzure 7 年前

您可以轻松使用 .map() 用于转换所需数据的函数:

isMatchedCountLessThanTotalCountMessage() {
    return Observable.combineLatest(
        this.getMatchedEventsCount(),
        this.getTotalEventsCount(),
    )
        .map(([intA, intB]) => {
            return intA > intB ? '(results ARE filtered)' : '(results are not filtered)'
        })
}

Alexander Mills 7 年前

这是可行的,尽管我们可能会使用一些不可观察的东西。拉链

 isMatchedCountLessThanTotalCount() {
    return Observable.create(obs => {
      return Observable.zip(
        this.getMatchedEventsCount(),
        this.getTotalEventsCount()
      )
      .subscribe(v => {
        if ((v[1] - v[0]) > 0) {
          obs.next('(results ARE filtered)')
        }
        else {
          obs.next('(results are not filtered)');
        }
      });
    });
  }

实际上,使用所谓的“投影函数”有一种更简单的方法:

  isMatchedCountLessThanTotalCount() {
    return Observable.combineLatest(
      this.getMatchedEventsCount(),
      this.getTotalEventsCount(),
      function (one, two) {
        if ((two - one) > 0) {
          return '(results ARE filtered)'
        }
        return '(results are not filtered)';
      }
    )
  }

Observable.combineLatest() 类似于 Observable.zip() 但它不会等待来自所有可观察对象的新值,而是会激发第一个新值。