将UITextField或按钮与viewModel绑定

Question

I have been facing an issue with binding UITextField or button with observables in viewModel.

class VM {
    var emailObservable: Observable<String?> = Observable.just("")
}

I have this observable for email in my viewModel and in controller. When i try to bind my textfield with it, it gives me error

Cannot invoke 'bind' with an argument list of type '(to: Observable)'.

But when i replace the observables with Variable, it works fine.

Can someone please help me with this. I found answers which mainly include passing the observable in the init method of viewModel, but i don't want to pass it in the init method.

This is the link i found for binding but it is through init method.

How to bind rx_tap (UIButton) to ViewModel?

Answer 1

I think here what you looking for:

final class ViewModel {

    private let bag = DisposeBag()
    let string = BehaviorSubject<String>(value: "")

    init() {
        string.asObservable().subscribe(onNext: { string in
            print(string)
        })
        .disposed(by: bag)
    }

}

final class ViewController: UIViewController {

    @IBOutlet weak var textField: UITextField!

    private let bag = DisposeBag()
    private var viewModel: ViewModel!

    override func viewDidLoad() {
        super.viewDidLoad()

        viewModel = ViewModel()

        textField.rx.text
            .orEmpty
            .bind(to: viewModel.string)
            .disposed(by: bag)
    }

}

Note, as @MaximVolgin mentioned Variable is deprecated in RxSwift 4 , so you can use BehaviorSubject or other that's up to you.

---

UPD.

Implementation with Observable only.

final class ViewModel {

    private let bag = DisposeBag()

    var string = "" {
        didSet {
            print(string)
        }
    }

    init(stringObservable: Observable<String>) {
        stringObservable.subscribe(onNext: { string in
            self.string = string
        })
        .disposed(by: bag)
    }

}

final class ViewController: UIViewController {

    @IBOutlet weak var textField: UITextField!

    private let bag = DisposeBag()
    private var viewModel: ViewModel!

    override func viewDidLoad() {
        super.viewDidLoad()

        viewModel = ViewModel(stringObservable: textField.rx.text.orEmpty.asObservable())
    }

}

As you can see, your solution can be implemented using Observable , not Variable or any kind of Subject . Also should be mentioned that in most cases this is not the final logic (just bind textField or whatever to some variable). There can be some validation, enable/disable, etc. logic. For this cases RxSwift provide Driver . Also nice example about differences in using Observable and Driver for one project can be found here (by RxSwift).

Answer 2

Method .bind(to:) binds to an Observer , not Observable .

Variable (deprecated in RxSwift v4) is a special-purpose Subject .

Subject s are by definition both Observer and Observable .

This is what .bind(to:) does inside -

public func bind<O: ObserverType>(to observer: O) -> Disposable where O.E == E {
    return self.subscribe(observer)
}

UPDATE:

How to avoid passing observables in .init() of VM:

// inside VM:

fileprivate let observableSwitch: BehaviorSubject<Observable<MyValue>>
fileprivate let myValueObservable = observableSwitch.switchLatest()

// instead of passing in init:

public func switch(to observable: Observable<MyValue>) {
  self.observableSwitch.onNext(observable)
}

Answer 3

Take a subject of variable type in ViewModel class:

class ViewModel{

//MARK: - local Variables
var emailText = Variable<String?>("")
}       

Now create object of viewmodel class in viewController class and bind this emailtext variable to textfield in viewcontroller.Whenever textfield text will change then it emailText of viewmodel gets value.

txtfield.rx.text
        .bindTo(viewModel.emailText).addDisposableTo(disposeBag)

Answer 4

Instead of

emailTextfield.rx.text.asObservable().bind(to: viewModel.emailObservable).disposed(by: disposeBag)

use this code

viewModel.emailObservable.bind(to: noteField.rx.text).disposed(by: disposeBag)

Probably, you want to make two way binding , so read more about it here

Answer 5

Try this,

override func viewDidLoad() {
        super.viewDidLoad()
        _ = userNameTextField.rx.text.map { $0 ?? "" }.bind(to: viewModel.userName)
    }

in viewModel class,

class ViewModel{
   var userName: Variable<String> = Variable("")
}