Question

说我有这个：

  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是这样的：

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

随着价值观的变化，这些Observable会触发整数。无论何时从任何一个值触发一个值，我想比较两者中最近的两个值，我该怎么做？

我想要做的是从方法

返回一个布尔值

所以我可以在HTML中显示：

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

我认为Observable.zip可以解决这个问题：

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
    });
  }

Answer 1

您可以轻松使用.map()函数转换所需的数据：

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

Answer 2

虽然我们可以使用Observable.zip之外的其他东西，但是这样可行。

 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)');
        }
      });
    });
  }

实际上有一种更简单的方法可以使用所谓的“投影函数”：

  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()与Observable.zip()类似，但会触发第一个新值，它不会等待来自所有可观察对象的新值。

比较来自多个BehaviorSubjects

2 个答案: