ViewController not being deallocated due to internal retain cycle

Question

Some of my view controllers don't get deallocated after being popped from view. I've gotten rid of the other strong references so I'm left with this internal retain cycle held through a reference form _externalObjectsTableForViewLoading. It's a private UIViewController property so I'm unable to clear it myself. I don't know if iOS has an API to clear it or why it's not being cleared after popping the view controller.

I've tested with with my app running in Release mode both in iOS 11 and 12. Running the app in Instruments renders the same stairs pattern seen in Xcode with the view controllers being retained.

Any ideas? Thanks in advance!

Answer 1

In your problem, is one viewController accessing another viewController? Our problem is that there was a non weak reference to a callback in another viewController.

As mentioned in your and in other posts on this, _externalObjectsTableForViewLoading is a viewController private property, but a storyboard related property. This leads me to think that your code has strong references to another object that is a view controller through a callback or through a direct property reference to its instance.

Answer 2

I had a similar problem. I fixed it using this:

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    viewModel?.viewWillDisappear()

    if isMovingFromParent || self.parent?.isBeingDismissed == true {
        viewModel = nil
        tableViewDataSource = nil
        view = nil
    }
}

By removing lines one by one in:

viewModel = nil
tableViewDataSource = nil
view = nil

I found that tableViewDataSource was causing a problem.

To debug deinit of ViewController I used this:

deinit {
    print("[Memory] \(String(describing: self)) deinit")
}