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In ReactiveCocoa, what's the difference between the subscribeError: method vs. catch:? Why would you want to return a signal in catch:?
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Example 1: Throw error on subscriptionconst source = throwError('This is an error! '); //output: 'Error: This is an error!
Angular CatchError is an RxJs Operator. We can use it to handle the errors thrown by the Angular Observable. Like all other RxJs operators, the CatchError also takes an observable as input and returns an observable (or throws an error).
Good Error Handling Always put the “catchError” operator inside a switchMap (or similar) so that it only ends the API call stream and then returns the stream to the switchMap, which continues the Observable.
-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."
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:.
Examples of what you could do in -catch::
[RACSignal empty] if you want to fail silently and not throw an error.[RACSignal error:err] if you want to rethrow the error after doing something, or perhaps you want to transform the error.
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