Core Text / NSStringDrawing - CFAttributedStringRef / NSAttributedString - changing font size

Question

Case: The attributed string is already created. How can the size of the string be altered?

I'm guessing we could either

A) Update pointSize for all fonts in the attributed string

B) Draw the attributed string with some transform

Answer 1

This works fine on both Mac OS and iOS

@implementation NSAttributedString (Scale)

- (NSAttributedString *)attributedStringWithScale:(double)scale
{
    if(scale == 1.0)
    {
        return self;
    }

    NSMutableAttributedString *copy = [self mutableCopy];
    [copy beginEditing];

    NSRange fullRange = NSMakeRange(0, copy.length);

    [self enumerateAttribute:NSFontAttributeName inRange:fullRange options:0 usingBlock:^(UIFont *oldFont, NSRange range, BOOL *stop) {
        double currentFontSize = oldFont.pointSize;
        double newFontSize = currentFontSize * scale;

        // don't trust -[UIFont fontWithSize:]
        UIFont *scaledFont = [UIFont fontWithName:oldFont.fontName size:newFontSize];

        [copy removeAttribute:NSFontAttributeName range:range];
        [copy addAttribute:NSFontAttributeName value:scaledFont range:range];
    }];

    [self enumerateAttribute:NSParagraphStyleAttributeName inRange:fullRange options:0 usingBlock:^(NSParagraphStyle *oldParagraphStyle, NSRange range, BOOL *stop) {

        NSMutableParagraphStyle *newParagraphStyle = [oldParagraphStyle mutableCopy];
        newParagraphStyle.lineSpacing *= scale;
        newParagraphStyle.paragraphSpacing *= scale;
        newParagraphStyle.firstLineHeadIndent *= scale;
        newParagraphStyle.headIndent *= scale;
        newParagraphStyle.tailIndent *= scale;
        newParagraphStyle.minimumLineHeight *= scale;
        newParagraphStyle.maximumLineHeight *= scale;
        newParagraphStyle.paragraphSpacing *= scale;
        newParagraphStyle.paragraphSpacingBefore *= scale;

        [copy removeAttribute:NSParagraphStyleAttributeName range:range];
        [copy addAttribute:NSParagraphStyleAttributeName value:newParagraphStyle range:range];
    }];

    [copy endEditing];
    return copy;
}

@end

Happy coding