Sorry. I am confused what is binding in Rxswift. As far as I know, observable
won't produce value unless a observer subscribed on it, e.g myObservable.subscribe(onNext: {})
.
But when I read the follow line of code:
// in LoginViewModel.swift
init() {
isValid = Observable.combineLatest(username.asObservable(), password.asObservable()) { (username, password) in
return !username.isEmpty && !password.isEmpty
}
}
// in LoginViewController.swift
viewModel.isValid.bind(to: loginButton.rx.isEnabled).disposed(by: disposeBag)
I am confused here why the isValid
Observable is able to be observed without calling a subscribe
method on it?
Why we can just call bind(to:) in LoginViewController.swift
without calling something like viewModel.isValid.subscribe(...)
Look at the implementation of bind(to: )
public func bind<O: ObserverType>(to observer: O) -> Disposable where O.E == E {
return self.subscribe(observer)
}
Subscribe is called inside.
Regarding your statement
As far as I know, observable won't produce value unless a observer subscribed on it
This is only true for cold observables. Let me quote from RxSwift docs
When does an Observable begin emitting its sequence of items? It depends on the Observable. A “hot” Observable may begin emitting items as soon as it is created, and so any observer who later subscribes to that Observable may start observing the sequence somewhere in the middle. A “cold” Observable, on the other hand, waits until an observer subscribes to it before it begins to emit items, and so such an observer is guaranteed to see the whole sequence from the beginning.