catch: 和 subscribeError 之间的区别:

问题描述

在 ReactiveCocoa 中，subscribeError: 方法与 catch 有什么区别:?为什么要在 catch: 中返回信号?

In ReactiveCocoa, what's the difference between the subscribeError: method vs. catch:? Why would you want to return a signal in catch:?

推荐答案

-subscribeError: 实际订阅:这是行尾.而 -catch: 只是将信号转换为新信号(实际上并不订阅).把信号想象成一个程序.当您 -subscribeError: 时，您是在告诉计算机我想运行这个程序，但我只想在它出错时收到您的回复."当您 -catch: 时，您是在说我的这个程序可能会抛出错误，我想根据旧程序创建一个新程序，以不同方式处理该错误."

-subscribeError: actually subscribes: this is the end of the line. Whereas -catch: simply transforms a signal into a new signal (and doesn't actually subscribe). Think of the signal like a program. When you -subscribeError:, you are telling the computer "I want to run this program, but I only want to hear back from you if it errors out." When you -catch:, you are saying "I've got this program that may throw an error, and I want to make a new one based on the old one that handles that error differently."

必须在 -catch: 中返回信号的原因是它不仅仅是为了抑制错误:它实际上是为了响应错误.一旦原始信号出错，它就像消失一样好:如果你想让结果信号在失败后继续运行，你必须在 -catch: 中给出一个新信号.

The reason you have to return a signal in -catch: is that it is not simply for squelching errors: it is actually for responding to errors. Once the original signal has errored out, it's as good as gone: if you want the resultant signal to keep going after a failure, you have to do give a new signal in -catch:.

您可以在 -catch: 中执行的操作示例:

Examples of what you could do in -catch::

1. 如果您想静默失败而不抛出错误，请返回 [RACSignal empty].
2. 返回 [RACSignal error:err] 如果你想在做某事后重新抛出错误，或者你想转换错误.
3. 返回一些您想要订阅的其他信号，以防第一个信号出错.

1. Return [RACSignal empty] if you want to fail silently and not throw an error.
2. Return [RACSignal error:err] if you want to rethrow the error after doing something, or perhaps you want to transform the error.
3. Return some other signal that you want to subscribe to in case the first one errors out.

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