NSAttributedString字符串属性类

 //定义一个可变字符串属性对象aStr
 NSMutableAttributedString *aStr = [[NSMutableAttributedString alloc]initWithString:str];
 //定义一个字典类对象dic存储设置的属性值，这里设置字体为粗体
 NSDictionary *dic = @{NSFontAttributeName:[UIFont boldSystemFontOfSize:self.myLabel.font.pointSize]   ,NSBackgroundColorAttributeName:[UIColor redColor]};
 //定义要改变的字符串的范围
     NSRange myRange = [str rangeOfString:title];
 //调用aStr对象的setAttributes方法设置属性
     [aStr setAttributes:dic range:myRange];
 //把aStr对象赋给Label
     self.myLabel.attributedText = aStr;