如何从订阅的RACSignal获取错误值?

你使用的语法让我觉得你在使用Swift,在这种情况下,你不应该使用RACSignal,你应该用 .toSignalProducer()

func sendSuccessOrNot() -> RACSignal {
    return RACSignal.createSignal { (subscriber) -> RACDisposable! in
        let test = true
        if (test) {
            subscriber.sendNext("Value")
            subscriber.sendCompleted()
        } else {
            subscriber.sendError(NSError(domain: "", code: 0, userInfo: nil))
        }
        return RACDisposable(block: {})
    }
}

controller.sendSuccessOrNot().toSignalProducer().on(next: { value in
    print("next: \(value)")
}, 
failed: { error in
    print("failed: \(error)")
}).start()

如果您仍在使用RAC 2,那么应该是

controller.sendSuccessOrNot().subscribeNext({ value in
    print("next: \(value)")
}, error: { error in
    print("failed: \(error)")
})