解决使用NSMutableAttributedString 设置不同字体，文字不能居中对齐

• 问题描述

使用NSMutableAttributedString设置不同字体，

     int  a = 50;
     int b = 10;

    NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:@"10元抵现券"];
    [attStr addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:a] range:NSMakeRange(0, 2)];
    [attStr addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:b] range:NSMakeRange(2, attStr.length - 2)];
//     [attStr addAttribute:NSBaselineOffsetAttributeName value:@(0.36 * (a - b)) range:NSMakeRange(2, attStr.length - 2)];
    label.attributedText = attStr;

文字不能居中对齐；如图：

• 解决方法
  NSMutableAttributedString 添加NSBaselineOffsetAttributeName这个Attribute

[attStr addAttribute:NSBaselineOffsetAttributeName value:@(0.36 * (a - b)) range:NSMakeRange(2, attStr.length - 2)];

value = 0.36 * (大字号 - 小字号)

    int  a = 50;
    int b = 10;

    NSMutableAttributedString *attStr = [[NSMutableAttributedString alloc] initWithString:@"10元抵现券"];
    [attStr addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:a] range:NSMakeRange(0, 2)];
    [attStr addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:b] range:NSMakeRange(2, attStr.length - 2)];
     [attStr addAttribute:NSBaselineOffsetAttributeName value:@(0.36 * (a - b)) range:NSMakeRange(2, attStr.length - 2)];
    label.attributedText = attStr;

• 效果图