A category to allow setting dynamic type via Classy

stylesheet.cas

UILabel {
  font-text-style: text-style-headline
}

UILabel+StyleExtensions.h

#import <UIKit/UIKit.h>

@interface UILabel (StyleExtensions)

@property (nonatomic, strong) NSString *fontTextStyle;

@end

UILabel+StyleExtensions.m

#import "UILabel+StyleExtensions.h"
#import <Classy/Classy.h>
#import <objc/runtime.h>

@implementation UILabel (StyleExtensions)

- (NSString *)fontTextStyle {
    return objc_getAssociatedObject(self, @selector(fontTextStyle));
}

- (void)setFontTextStyle:(NSString *)fontTextStyle {
    NSDictionary *textStyleMap = @{
                                   @"text-style-headline": UIFontTextStyleHeadline,
                                   @"text-style-subheadline": UIFontTextStyleSubheadline,
                                   @"text-style-body": UIFontTextStyleBody,
                                   @"text-style-footnote": UIFontTextStyleFootnote,
                                   @"text-style-caption1": UIFontTextStyleCaption1,
                                   @"text-style-caption2": UIFontTextStyleCaption2
                                   };
    if ([textStyleMap valueForKey:fontTextStyle]) {
        objc_setAssociatedObject(self, @selector(fontTextStyle), [textStyleMap valueForKey:fontTextStyle], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        self.font = [UIFont preferredFontForTextStyle:[textStyleMap valueForKey:fontTextStyle]];
    }
}

@end