RxSwift: Observe viewDidLoad from view model without Subjects - swift

Question

I have a dependency problem with my UIViewController and my view model.
Basically I want to listen the viewDidLoad event inside my view model.
At the moment I have a Class A which instantiates view model and UIViewController with parameter the viewModel, so:
let viewModel = ViewModel()
let viewController = UIViewController(viewModel)
and I've created a RxCocoa extension for the viewDidLoad:
var viewDidLoad: Observable<Void> {
return self.sentMessage(#selector(Base.viewDidLoad)).map { _ in Void() }
}
now I'm stuck to bind this rx.viewDidLoad to an observable inside my view model. I am able to do it with Subjects but I want a reactive approach using just Observable.
I know that I could inject rx.viewDidLoad as constructor parameter of the view model but in this way I'd break my architecture and I don't want to allow the UIViewController to instantiate the view model internally but I want to keep it as a injected dependency.
Any suggestions?
Thanks
Solution
Thank to #tomahh I've used this solution:
My view controller:
override func configure(viewModel: ViewModel) {
viewModel.bindViewDidLoad(rx.viewDidLoad)
}
My view model:
func bindViewDidLoad(_ viewControllerDidLoad: Observable<Void>) {
//Create observers which depend on viewControllerDidLoad
}

Answer 1

Because ViewController already knows about view model, it could set a property on ViewModel at initialisation time
class ViewController: UIViewController {
init(_ viewModel: ViewModel) {
viewModel.viewDidLoad = self.rx.viewDidLoad
}
}
And then, observables in ViewModel could be defined as computed property deriving viewDidLoad
struct ViewModel {
var viewDidLoad: Observable<Void> = .never()
var something: Observable<String> {
return viewDidLoad.map { "Huhu, something is guuut" }
}
}

Answer 2

If anybody needs that rx properties here is a ready to use solution, inspired by the code of #marco-santarossa
extension Reactive where Base: UIView {
var willMoveToWindow: Observable<Bool> {
return self.sentMessage(#selector(Base.willMove(toWindow:)))
.map({ $0.filter({ !($0 is NSNull) }) })
.map({ $0.isEmpty == false })
}
var viewWillAppear: Observable<Void> {
return self.willMoveToWindow
.filter({ $0 })
.map({ _ in Void() })
}
var viewWillDisappear: Observable<Void> {
return self.willMoveToWindow
.filter({ !$0 })
.map({ _ in Void() })
}
}

Answer 3

let viewDidAppear = rx.sentMessage(#selector(UIViewController.viewDidAppear(_:)))
.mapToVoid()
.asDriver(onErrorJustReturn: ())