How to selectively italicize text when using +[UIFont preferredFontForTextStyle:xxx]?

Question

I create an NSMutableAttributedString like this:

UIFont *font = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];
NSDictionary *attributes = @{ NSFontAttributeName: font };
NSMutableAttributedString *attrStr = [[NSMutableAttributedString alloc] initWithString:str attributes:attributes];

Now I'd like to italicize specific ranges of attrStr via something like:

- (void)setAttributes:(NSDictionary *)attrs range:(NSRange)range;

but since I never asked for a specific font I'm not sure how I'd go about it.

Answer 1

// Create the normal body style font    
UIFont *font = [UIFont preferredFontForTextStyle:UIFontTextStyleBody];

// Get the font's descriptor and add the italics trait
UIFontDescriptor *fontDesc = [font fontDescriptor];
fontDesc = [fontDesc fontDescriptorWithSymbolicTraits:UIFontDescriptorTraitItalic];

// Create the italicized font from the descriptor
UIFont *italicsFont = [UIFont fontWithDescriptor:fontDesc size:font.pointSize];

// Create the attributes dictionary that we'll use to italicize parts of our NSMutableAttributedString
NSDictionary *italicsAttributes = @{ NSFontAttributeName: italicsFont };

Answer 2

Used RobertJoseph's answer to make a Swift 3 extension.

extension UIFont {

    class func preferredItalicFont(forTextStyle style: UIFontTextStyle) -> UIFont? {
        return UIFont.preferredFont(forTextStyle: style).italicisedVariant
    }

    var italicisedVariant: UIFont? {
        guard let italicDescriptor = fontDescriptor.withSymbolicTraits(.traitItalic) else { return nil }
        return UIFont(descriptor: italicDescriptor, size: pointSize)
    }

}