RxSwift/RxCocoa: prevent UITextField from having more than ... characters

Question

I would like to have a UITextField configured with RxSwift/RxCocoa so that it only contains up to ... characters. I do not want to use the UITextFieldDelegate for this but would love to achieve this with RxSwift/RxCocoa. Is there a way to do this?

Answer 1

Sure:

textField.rx.controlEvent(.editingChanged).subscribe(onNext: { [unowned self] in
    if let text = self.textField.text {
        self.textField.text = String(text.prefix(40))
    }
}).disposed(by: disposeBag)

In this example, the textfield is limited to 40 characters.

Edit:

Keeping the previous value when the limit is reached.

textField.rx.text.orEmpty
.scan("") { (previous, new) -> String in
    if new.count > 40 {
        return previous ?? String(new.prefix(40))
    } else {
        return new
    }
}
.subscribe(textField.rx.text)
.disposed(by: disposeBag)

This can probably be adapted to respect other rules...

Please note however that when reaching the character limit, your cursor will jump to the end of the textField.