RxJS:Observable.never()保持订阅状态 [英] RxJS: Observable.never() keeps like subscription

问题描述

我正在使用rxjs 5.5.6.

I'm using rxjs 5.5.6.

我已创建此代码以显示其行为:

I've created this code in order to show the behavior:

Observable.of(1, 2)
    .do(a => {
        console.log(a);
        let d:string = null;
        let r = d.length;  // it raises an null exception
    })
    .catch(() => {
        console.log("error catched");  //exception is capture here
        return Observable.never();
    })
    .subscribe();

我期望输出为:

1
error catched
2
error catched

但是，输出为:

1
error catched

这意味着，尽管在.catch(...)方法链上返回了Observable.never()，预订仍会终止.

It means, the subscription terminates despite of an Observable.never() is returned on .catch(...) method chain.

有什么想法吗?

真实案例

this.subs = Observable
    .merge(this.$searchQuery, this.$lazyQuery)
    .do(() => this.loadingPage())
    .map(filter => this.buildURL(user, app, filter))
    .switchMap(url => this.service.getItemsFromService(url))
    .map(response => this.buildPage(response))
    .do(page => this.loadedPage(page))
    .catch(() => {
        this.loadedPage(pojo.Page.EMPTY);
        return Observable.never();
    })
    .takeUntil(this.$unsubscribe)
    .subscribe();

推荐答案

@frido的所有解释都是正确的.有了这个答案，我想补充:

Yes all the explanation by @frido is correct. With that answer I would like to add:

如果您想捕获任何特定的Observable本身发生的任何错误(例如HTTP请求)，则需要在该特定的错误Observable中对其进行处理.

If you want to capture any error occuring in any particular Observable itself(say an HTTP request) then you need to handle it in that particular erroring Observable.

  let correct = Observable.of("correct")
  let inCorrect = Observable.throw('inCorect')

  let obs = [inCorrect, correct];
  let handledObs = obs.map(eachObs => {
    return eachObs.catch((e) => {
      console.log("Individual handler, Good Catch!");
      return Observable.of("I am tampered");
    })
  })

  forkJoin(...handledObs)
  .do(a => {
      console.log(a);
  })
  .catch(() => {
      console.log("error catched");
      return Observable.never();
  })
  .subscribe(data => {
    console.log(`data`, data)
  },(e) => {
      console.log(`error`, e)
  });

}

在此处查看示例: https://stackblitz.com/edit/angular-7mmhn7?file=src/app/app.component.ts

编辑

但是，当我查看您的代码时，在我看来您正在尝试记录某些内容，并且返回的数据可能没有length属性，即使在这种情况下，您也想继续进行流操作.如果是这样，则可以在do()

However when I look at your code, it looks to me that you are trying to log something and the returned data may not have a length property, even in that case you want to proceed with the stream. If this is true then you can add a simple try catch under do()

  from([1, 2])
  .do(a => {
      try {
        console.log(a);
        let d:string = null;
        let r = d.length;
      } catch(e) {
        console.log(`catched under do`, e)
      }
  })
  .catch(() => {
      console.log("error catched");
      return Observable.of('catched');
  })
  .subscribe(data => {
    console.log(`data`, data)
  },(e) => {
      console.log(`error`, e)
  });

这里是一个示例: https://stackblitz.com/edit/angular-bcrava?file=src/app/app.component.ts

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