Controls not dimming when view controller is presented locally and alert displayed - ios

Question

When I present a UIAlertController over a view controller, the controls are dimmed as expected.
However, if the same view controller is itself modally presented, the display of the alert controller does not dim the controls (the two buttons remain blue).
How do I make a presented view controller itself handle presentations correctly, and dim its controls?
Here is a small example project. The relevant code is in MainViewController.swift.

Answer 1

The best workaround I have so far is to use a customized UIAlertController subclass to set the tintAdjustmentMode alongside its appear/disappear animations, using the transitionCoordinator:
/// A `UIAlertController` that can udpates its presenting view controller's `tintAdjustmentMode` code as it appears and disappears
class TintAdjustingAlertController: UIAlertController {
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
animatePresentingViewTintAdjustmentMode(tintAdjustmentMode: .dimmed, forViewControllerAtKey: .from)
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
animatePresentingViewTintAdjustmentMode(tintAdjustmentMode: .automatic, forViewControllerAtKey: .to)
}
private func animatePresentingViewTintAdjustmentMode(tintAdjustmentMode mode: UIView.TintAdjustmentMode, forViewControllerAtKey key: UITransitionContextViewControllerKey) {
transitionCoordinator?.animate(alongsideTransition: { context in
if let presentingNavigationController = context.viewController(forKey: key) as? UINavigationController {
presentingNavigationController.navigationBar.tintAdjustmentMode = mode
presentingNavigationController.viewControllers.forEach { $0.view.tintAdjustmentMode = mode }
} else if let presentingViewController = context.viewController(forKey: key) {
presentingViewController.view.tintAdjustmentMode = mode
}
}, completion: nil)
}
}
This works, but I hope not to have to pepper it throughout my code. Would still love to know a) if there is a simple way to make this work as expected, or b) if this is indeed an iOS bug, is there a more elegant workaround?
I have also submitted a radar for this: http://www.openradar.me/radar?id=6113750608248832