Reactivecocoa: Very basic TextField/TextView two way binding to viewModel

[tunidev]

I have a textfield and a textView in my UIViewController and in my ViewModel I have two String variable, I want to bind the textField to variabletitle and the textView to variable textBody. In RAC2 it's straight forward with RAC but what about RAC4 and Swift2 ?

I found this in StackOverFlow :

        let producer = textField.rac_textSignal().toSignalProducer()
            .flatMapError { error in
                return SignalProducer<AnyObject?, NoError>.empty
            }
            .map { text in Int(text as! String) }

        self.viewModel.title <~ producer

but I get Use of undeclared type 'NoError' so I changed it to NSError but now I get : Binary operator '<~' cannot be applied to operands of type 'String' and 'SignalProducer<Int?, NSError>' (aka 'SignalProducer<Optional<Int>, NSError>')

self.viewModel.title is a simple var title = ""

I know that I can do that :

        textField.rac_textSignal()
            .toSignalProducer()
            .map { text in text as! String } // AnyObject -> String
            .filter { string in string.characters.count > 0 } // String -> Bool
            .startWithNext { [weak self] (text) in
                self?.viewModel.title = text
        }

but why all that code to just bind and the use of startWithNext and [weak self] :(

[andersio]

Swift does not have macro or KVC in objects, so there is no binding magic like RAC(). Bindings in Swift are intended to target Property types.

P.S. You may need import enum Result.NoError for the NoError type.

[andersio]

In ReactiveCocoa 5.0, primitives like reactive.text and reactive.textValues are provided in various UIKit/AppKit controls and views.

textField.text <~ viewModel.title.producer
viewModel.title <~ textField.textValues

Although we do not have a bidirectional binding system in ReactiveCocoa yet, the above snippet would work without an infinite feedback loop.

This only works for bindings with controls though. Bidirectional bindings between properties, if you ever need it, are impossible without a mediator in between.

[lukaskubanek]

@andersio I’ve seen that you started the work on support for bidirectional bindings on MutableProperty in ReactiveCocoa/ReactiveSwift#181 and ReactiveCocoa/ReactiveSwift#182 a couple of years ago. Are there any plans to continue at some point, or is this kind of binding out of scope for ReactiveCocoa/ReactiveSwift? I’m just curious to hear an update on that since I run into this problem quite often, and it always brings me to this GitHub issue. 😉