ContentSize.swift

protocol ContentSizable {
    func ad_updateContentSize()
}

extension UIView : ContentSizable {
    func ad_updateContentSize() {
        subviews.forEach { $0.ad_updateContentSize() }
    }
}

extension UIViewController : ContentSizable {
    func ad_updateContentSize() {
        view.ad_updateContentSize()
    }
}

// This protocol allow to start/end observing `NSNotification.Name.UIContentSizeCategoryDidChange`
// `UIViewController` provides default implementation
protocol ContentSizeObservable {
    func startObservingContentSize()
    func endObservingContentSize()
}

extension UIViewController : ContentSizeObservable {
    func startObservingContentSize() {
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(preferredContentSizeChanged),
            name: NSNotification.Name.UIContentSizeCategoryDidChange,
            object: nil
        )
    }

    func endObservingContentSize() {
        NotificationCenter.default.removeObserver(
            self,
            name: NSNotification.Name.UIContentSizeCategoryDidChange,
            object: nil
        )
    }

    @objc private func preferredContentSizeChanged() {
        ad_updateContentSize()
    }
}