Simple textfield validator using Reactive Cocoa - swift

Question

I am testing ReactiveCocoa in a playground. I would like to test for the validity of a string before performing a network request.
I am not sure how to combine the textfield signal and the validation signal tho. The part of the code that is marked [??] => what is the right way to do that filter?
var textField = UITextField()
textField.text = "http://localhost:3000/users.json"
let searchStringsProducer = textField.rac_textSignal().toSignalProducer()
let searchStringValidProducer = searchStringsSignal.toSignalProducer().map{
text in
(text as! String).containsString("http")
}
// this produces a ReactiveCocoa.SignalProducer<(Optional<AnyObject>, Bool), NSError>.
let searchStringCombined = combineLatest(searchStringsProducer, searchStringValidProducer)
// turns the simple search results into a signal
let searchResults = searchStringCombined
// [??] i would like to ONLY execute on the rest of the actions if it is valid
.map{ // what do i do here before passing on to the network API }
.flatMap(FlattenStrategy.Latest) {
latestStr -> SignalProducer<[AnyObject], NSError> in
return requestJSON(latestStr, parameters: nil)
.flatMapError { error in
print("Network error occurred: \(error)")
return SignalProducer.empty
}
}.observeOn(uis)

Answer 1

let searchStringValidProducer = searchStringsSignal.toSignalProducer().map { text in
(text as! String).containsString("http")
}
let searchStringCombined = combineLatest(searchStringsProducer, searchStringValidProducer)
This pattern is troubling, because when searchStringsProducer sends a value, searchStringCombined will send two values -- one for the new string, and one for the new boolean. It would be neater to define this signal like this:
let searchStringCombined = searchStringsSignal.toSignalProducer().map { text in
(text, (text as! String).containsString("http"))
}
Which gives you the same result.
But you don't need to define searchStringCombined at all, unless you're using it elsewhere. You should be able to get by with a simple filter:
searchStringsSignal.toSignalProducer().filter({ text in
(text as! String).containsString("http")
}).map({
/* whatever goes here */
}).flatMap(FlattenStrategy.Latest) {
/* perform network request */
}
filter is kind of like map, in that it takes a function and returns a signal. But it only lets some values through, allowing you to only make network requests based on the valid inputs.