MVVM-C with RxSwift: '[weak self]' in closure

Question

I'm working on an iOS project with RxSwift and I use the MVVM with coordinators pattern.

Here my implementation:

ViewModel:

// MARK: - Private

private let showNextViewSubject = PublishSubject<Void>()

// MARK: - Inputs

var showNextView: AnyObserver<Void> {
    return showNextViewSubject.asObserver()
}

// MARK: - Outputs

var didShowNextView: Observable<Void> {
    return showNextViewSubject.asObservable()
}

ViewController:

private func bindButton() {
    _ = button.rx.tap
        .bind(to: viewModel.showNextView)
        .disposed(by: disposeBag)
}

Coordinator:

self.viewModel.didShowNextView
        .subscribe(onNext: { [weak self] _ in
            self?.showNextView()
        })
        .disposed(by: disposeBag)

My problem is with the [weak self] _ in the coordinator: when I add it, self?.showNextView() is never called, but this works well when I remove it.

Do you know why?

Thanks, Romain

Answer 1

When you get rid of [weak self] the block creates a strong reference to self so that it's not deallocated when any other code is done using it. By making the reference weak self is free to be deallocated which is probably happening. This means there is no other object with a strong reference to self so it is nil and the call won't be made. Getting rid of it could create a retain cycle so you'll want to be careful of that.