普通字体转换成粗体

gistfile1.m

// Returns the bold version of a font. May return nil if there is no bold version.
UIFont *RNGetBoldFontForFont(UIFont *font) {
  UIFont *result = nil;
  
  CTFontRef ctFont = CTFontCreateWithName((__bridge CFStringRef)(font.fontName),
                                          font.pointSize, NULL);
  if (ctFont) {
    // You can't add bold to a bold font
    // (don't really need this, since the ctBoldFont check would handle it)
    if ((CTFontGetSymbolicTraits(ctFont) & kCTFontTraitBold) == 0) {
      CTFontRef ctBoldFont = CTFontCreateCopyWithSymbolicTraits(ctFont,
                                                                font.pointSize,
                                                                NULL,
                                                                kCTFontBoldTrait,
                                                                kCTFontBoldTrait);
      if (ctBoldFont) {
        NSString *fontName = CFBridgingRelease(CTFontCopyPostScriptName(ctBoldFont));
        result = [UIFont fontWithName:fontName size:font.pointSize];
        CFRelease(ctBoldFont);
      }
    }
    CFRelease(ctFont);
  }
  return result;
}