Two way binding in RxSwift

Question

I read the two way binding operator in sample code of RxSwift.

func <-> <T>(property: ControlProperty<T>, variable: Variable<T>) -> Disposable {
    let bindToUIDisposable = variable.asObservable()
        .bindTo(property)
    let bindToVariable = property
        .subscribe(onNext: { n in
            variable.value = n
        }, onCompleted:  {
            bindToUIDisposable.dispose()
        })

    return StableCompositeDisposable.create(bindToUIDisposable, bindToVariable)
}

When property changed, it will notify variable, and set the variable's value, while the variable's value is set, it will notify the property. I think it will lead to endless loop...

Answer 1

I believe you can just use bindTo 🙂. Here are implementations for ControlProperty <-> Variable and Variable <-> Variable:

infix operator <-> { precedence 130 associativity left }

func <-><T: Comparable>(property: ControlProperty<T>, variable: Variable<T>) -> Disposable {
    let variableToProperty = variable.asObservable()
        .distinctUntilChanged()
        .bindTo(property)

    let propertyToVariable = property
        .distinctUntilChanged()
        .bindTo(variable)

    return StableCompositeDisposable.create(variableToProperty, propertyToVariable)
}

func <-><T: Comparable>(left: Variable<T>, right: Variable<T>) -> Disposable {
    let leftToRight = left.asObservable()
        .distinctUntilChanged()
        .bindTo(right)

    let rightToLeft = right.asObservable()
        .distinctUntilChanged()
        .bindTo(left)

    return StableCompositeDisposable.create(leftToRight, rightToLeft)
}

Examples of ControlProperty <-> Variable (such as UITextField and UITextView) are in the RxSwiftPlayer project

// Example of Variable <-> Variable

let disposeBag = DisposeBag()
let var1 = Variable(1)
let var2 = Variable(2)

(var1 <-> var2).addDisposableTo(disposeBag)

var1.value = 10
print(var2.value) // 10

var2.value = 20
print(var1.value) // 20