ios同一个Label中的字符设置不同的字体

NSString* amountStr = @"$12";

NSMutableAttributedString *arrt = [[NSMutableAttributedStringalloc]initWithString:amountStr];

[arrt addAttribute:NSForegroundColorAttributeName value:[UIColor blueColor] range:NSMakeRange(0,1)];

[arrt addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(1, amountStr.length-1)];

[arrt addAttribute:NSFontAttributeNamevalue:[UIFontsystemFontOfSize:18]range:NSMakeRange(0,1)];

[arrt addAttribute:NSFontAttributeNamevalue:[UIFontsystemFontOfSize:30]range:NSMakeRange(1, amountStr.length-1)];

_amountLabel.attributedText = arrt;