可观察的-将2个诺言转换为可观察的 [英] Observable - converting 2 promises into an observable

问题描述

我有一个流行的场景，我需要创建一个承诺，该承诺返回返回到第二个承诺的数据. 如果第一个承诺失败，我需要取消第二个承诺. 在承诺"土地上，它看起来像这样:

I have a popular scenario where I need to create one promise that returns data which is fed to a second promise. If the first promise fails, I need to cancel the second promise. In 'Promise' land it would look something like this:

Fn1.doPromise( initialData )
  .then(info => {
        Fn2.doPromise( info )
              .then(result => {
                  //success - return result
              })
              .catch(error => {
                //error
              });
  })
.catch(error => {
  //cancel 2nd promise and show error
});

现在，我正在尝试使用Observables和RxJS之类的方法来学习最佳方法.谁能给我一个好的解决方案? 预先感谢！

Now I am trying to learn the best way to do this using Observables with something like RxJS. Can anyone give me a good solution ? Thank in advance !

推荐答案

RxJS处理错误的一般问题由

The general issue of error handling with RxJS is dealt with here. Main points are :

• 捕获错误(使用catch运算符，无论是在实例级别还是在类级别)
• 使用onErrorResumeNext
忽略错误
• 重试序列(使用retry)
• 确保清理(使用finally)
• 确保资源处置(使用finally或using)
• 延迟错误(使用mergeDelayError)

• Catching Errors (with catch operator, either at instance level or at class level)
• Ignoring Errors with onErrorResumeNext
• Retrying Sequences (with retry)
• Ensuring Cleanup (with finally)
• Ensuring Resource Disposal (with finally or using)
• Delaying Errors (with mergeDelayError)

关于您的特定问题，您可以使用 Rx.Observable.fromPromise 将诺言转换为可观察的； Rx.Observable.prototype.catch 在发生错误时及时捕获.

About your specific question you can use Rx.Observable.fromPromise to convert a promise into an observable; Rx.Observable.prototype.catch to catch errors as they occur.

Rx.Observable.fromPromise(Fn1.doPromise( initialData ))
  .flatMap(info => {
        return Rx.Observable.fromPromise(Fn2.doPromise( info ))
              .flatMap(result => {
                  //success - return result
                  // !! You must return an observable or a promise here !!
              })
              .catch(error => {
                //error
                // !! You must return an observable here !!
              });
  })
.catch(error => {
  //cancel 2nd promise and show error
  // !! You must return an observable here !!
});

示例:

• 第一个错误处理程序已激活
• 没有错误
• 内部错误处理程序已激活

• first error handler activated
• no error
• inner error handler activated

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