import RxSwift

// -- View Model
struct LoginViewModel {

    var username = Variable<String>("")
    var password = Variable<String>("")

    var isValid : Observable<Bool>{
        return Observable.combineLatest( self.username, self.password)
        { (username, password) in
            return username.characters.count > 0
                        && password.characters.count > 0
        }
    }
}

// ----- View Controller

import RxSwift
import RxCocoa

class LoginViewController {
    var usernameTextField: UITextField!
    var passwordTextField: UITextField!
    var confirmButton: UIBUtton!

    var viewModel = LoginViewModel()

    var disposeBag = DisposeBag()

    override func viewDidLoad(){
        super.viewDidLoad()
        usernameTextField.rx.text.bindTo(viewModel.username).addTo(disposeBag) passwordTextField.rx.text.bindTo(viewModel.username).addTo(disposeBag)

        //from the viewModel
        viewModel.rx.isValid.map{ $0 }
            .bindTo(confirmButton.rx.isEnabled)
    }
}