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Version Carthage Compatible License Platform Swift


If you're using MVVM with FRP, then chances are that you need to rely on UIViewController or UIApplication life cycle events to trigger signals. We can either do it by calling a method on the ViewModel, like kickstarter-ios

override func viewWillAppear(_ animated: Bool) {

or reactively using signal binding.

override func viewDidLoad() {
  rx.viewWillAppear.bind(to: viewModel.input.fetchData).disposed(by: disposeBag)

One way to make observations for the life cycle is to use sentMessage and methodInvoked which involve a lot of swizzlings 😱 We shouldn't use swizzlings, it is just asking for problem.

public extension Reactive where Base: UIViewController {
  public var viewWillAppear: ControlEvent<()> {
    let source = self.methodInvoked(#selector(Base.viewWillAppear)).mapVoid()
    return ControlEvent(events: source)

Instead, we can just use simple composition, that you can plug and play everywhere you want. See demo


  • ViewControllerLifeCycle for events related to UIViewController
  • AppLifeCycle for events related to UIApplication, equivalent to UIApplicationDelegate
  • Auto clean up upon deinit
  • Support iOS, tvOS



This works by embed a child view controller so that it can forward appearance method

After adding a child to a container, the container automatically forwards appearance-related messages to the child

All you need to do is to declare ViewControllerLifeCycle object and observe on it. Remember to keep this ViewControllerLifeCycle so it is not released !!

let viewController = LoginViewController()
let lifeCycle = ViewControllerLifeCycle(viewController: viewController)

_ = lifeCycle.viewWillAppear.subscribe(onNext: {
  print("viewWillAppear has been called")

For convenience, you can also use it directly by using rxLifeCycle

let viewController = LoginViewController()

_ = viewController.rxLifeCycle.viewDidAppear.subscribe(onNext: {
  print("viewDidAppear has been called")

Supported observables

  • viewWillAppear
  • viewDidAppear
  • viewWillDisappear
  • viewDidDisappear


There are times we need to refresh data when user go back to the app again, which is the UIApplicationWillEnterForeground event. All you need to do is to declare AppLifeCycle and observe on it. Under the hood, it listens to UIApplication notifications and publish the signals.

Remember to keep this AppLifeCycle so it is not released !!

let lifeCycle = AppLifeCycle()
_ = lifeCycle.didBecomeActive.subscribe(onNext: {
  print("didBecomeActive was called")

For convenience, you can also use it directly by using rxLifeCycle on UIApplication

let lifeCycle = AppLifeCycle()
_ = UIApplication.shared.rxLifeCycle.willEnterForeground.subscribe(onNext: {
  print("willEnterForeground was called")

Supported observables

  • didBecomeActive
  • willResignActive
  • didEnterBackground
  • willEnterForeground


RxLifeCycle is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'RxLifeCycle'

RxLifeCycle is also available through Carthage. To install just write into your Cartfile:

github "onmyway133/RxLifeCycle"

RxLifeCycle can also be installed manually. Just download and drop Sources folders in your project.


Khoa Pham, [email protected]


We would love you to contribute to RxLifeCycle, check the CONTRIBUTING file for more info.


RxLifeCycle is available under the MIT license. See the LICENSE file for more info.

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