UILabel subclass that automatically adjusts the font when the global dynamic type setting changes.

DynamicTypeLabel.swift

//
//  DynamicTypeLabel.swift
//
//  Created by Indragie on 10/16/14.
//  Copyright (c) 2014 Indragie Karunaratne. All rights reserved.
//

import UIKit

class DynamicTypeLabel : UILabel {
    private var textStyle: String?
    
    func commonInit() {
        textStyle = textStyleForCurrentFont()
        NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("dynamicTypeSettingChanged"), name: UIContentSizeCategoryDidChangeNotification, object: nil)
    }
    
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonInit()
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    
    deinit {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }
    
    @objc func dynamicTypeSettingChanged() {
        if let textStyle = textStyle {
            font = UIFont.preferredFontForTextStyle(textStyle)
        }
    }
    
    func textStyleForCurrentFont() -> String? {
        let styles = [
            UIFontTextStyleBody,
            UIFontTextStyleHeadline,
            UIFontTextStyleSubheadline,
            UIFontTextStyleFootnote,
            UIFontTextStyleCaption1,
            UIFontTextStyleCaption2
        ]
        for style in styles {
            if font == UIFont.preferredFontForTextStyle(style) {
                return style
            }
        }
        return nil
    }
}