RxViewController.swift

extension Reactive where Base: UIViewController {

    /// Observable, triggered when the view has appeared for the first time
    public var firstTimeViewDidAppear: Single<Void> {
        return sentMessage(#selector(Base.viewDidAppear)).map { _ in
            return Void()
        }.take(1).asSingle()
    }

    /// Observable, triggered when the view is being dismissed
    public var dismissed: ControlEvent<Bool> {
        let source = sentMessage(#selector(Base.dismiss))
                     .map { $0.first as? Bool ?? false }
        return ControlEvent(events: source)
    }

    /// Observable, triggered when the view appearance state changes
    public var displayed: Observable<Bool> {
        let viewDidAppearObs = sentMessage(#selector(Base.viewDidAppear))
                               .map { _ in true }
        let viewWillDisappearObs = sentMessage(#selector(Base.viewWillDisappear))
                                   .map { _ in false }
        return Observable<Bool>.merge(viewDidAppearObs, viewWillDisappearObs)
    }
}