How to make a UIFont bold or italic? - ios

Question

Having a UILabel with any font, how can I find out if it is already bold? Or how can I make it bold? In CSS, I have a font-weight attribute. I would like to have something similar.
Everything I found out so far is that you have to set the proper font name. However, this is unreliable. The bold version of Cochin is Cochin-Bold, but the bold version of ArialMT is not ArialMT-Bold but Arial-BoldMT, so it obviously does not suffice to append -Bold. (The bold version of a custom font could also have a totally different name).
What I can do is finding all fonts for the family of my given font.
__block UIFont *font = myLabel.font;
[[UIFont fontNamesForFamilyName:font.familyName] enumerateObjectsUsingBlock:^(NSString *fontName, NSUInteger idx, BOOL *stop) {
if ([fontName rangeOfString:#"bold" options:NSCaseInsensitiveSearch].location != NSNotFound) {
font = [UIFont fontWithName:fontName size:font.pointSize];
*stop = YES;
}
}];
myLabel.font = font;
But this does not work reliably. I can easily get a BoldItalic version. I could improve my check to avoid this, but it is not really a good solution.
Maybe CoreText can help here?

Answer 1

Maybe CoreText can help here?
CoreText uses its own font system, CTFont. If you're using that, you can do what you want:
CTFontRef font = CTFontCreateWithName((__bridge CFStringRef)name, size, NULL);
CTFontRef boldFont = CTFontCreateCopyWithSymbolicTraits(font, 0.0, NULL, kCTFontBoldTrait, kCTFontBoldTrait);
I suppose you could then get the name of the derived bold font:
CFStringRef boldName = CTFontCopyPostScriptName(boldFont);
...and use it to create a new UIFont:
UIFont *ret = [UIFont fontWithName:(NSString *)boldName size:size];
I don't know how quick this would be, but you could do it on app launch then cache the names.

Answer 2

Introduced with iOS 7, UIFontDescriptor is the tool for doing this.
To find out if the font is already bold, get the UIFontDescriptor of your font (via UIFont's fontDescriptor property), then call symbolicTraits, and inspect the resulting bitmask for UIFontDescriptorTraitBold.
Likewise, to find a bold version, take the font descriptor for the original font, and call - fontDescriptorWithSymbolicTraits:. You can then turn it back into a UIFont by calling + [UIFont fontWithDescriptor:size:].

Answer 3

UIFontDescriptorSymbolicTraits symbolically describes stylistic aspects of a font. The upper 16 bits is used to describe appearance of the font whereas the lower 16 bits for typeface. The font appearance information represented by the upper 16 bits can be used for stylistic font matching.
Swift 3
extension UIFont {
convenience init?(name: String, size: CGFloat, symbolicTraits: UIFontDescriptorSymbolicTraits) {
guard let descriptor = UIFontDescriptor(name: name, size: size).withSymbolicTraits(symbolicTraits) else { return nil }
self.init(descriptor: descriptor, size: size)
}
}