A `UINavigationController` that adjusts the font size of its large title labels to fit its content

LargeTitleAdjustingNavigationController.swift

import UIKit

/// A `UINavigationController` that adjusts the font size of its large title labels to fit its content
class TitleSizeAdjustingNavigationController: UINavigationController {
	var minimumScaleFactor: CGFloat = 0.5

	override func viewDidLayoutSubviews() {
		guard navigationBar.prefersLargeTitles else { return }

		updateLargeTitleLabels()
	}

	private func updateLargeTitleLabels() {
		largeTitleLabels().forEach {
			$0.adjustsFontSizeToFitWidth = true
			$0.minimumScaleFactor = minimumScaleFactor
		}
	}

	private func largeTitleLabels() -> [UILabel] {
		let subviews = recursiveSubviews(of: navigationBar)
		let labels = subviews.compactMap { $0 as? UILabel }
		let titles = viewControllers.compactMap { $0.title }
		let titleLabels = labels.filter {
			if let text = $0.text, titles.contains(text) {
				return true
			}
			return false
		}

		// 'large' title labels are identified by comparing font size
		let titleLabelFontSizes = titleLabels.map { $0.font.pointSize }
		let largeTitleLabelFontSize = titleLabelFontSizes.max()
		let largeTitleLabels = titleLabels.filter { $0.font.pointSize == largeTitleLabelFontSize }
		return largeTitleLabels
	}

	private func recursiveSubviews(of view: UIView) -> [UIView] {
		var result = [UIView]()
		for subview in view.subviews {
			result.append(subview)
			result += recursiveSubviews(of: subview)
		}
		return result
	}
}