NSInteger stringLength = ;

        stringLength = model.ToUserNickName.length;

        NSMutableAttributedString *str = [[NSMutableAttributedString alloc] initWithString:string];

        NSLog(@"textLength is %u", model.ToUserNickName.length);

        [str addAttribute:NSForegroundColorAttributeName value:[UIColor grayColor] range:NSMakeRange(,stringLength)];

        self.CommentContent.attributedText = str;     // self.CommentContent.attributedText  是一个 label

textField.placeholder = @"username is in here!";

[textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];

[textField setValue:[UIFont boldSystemFontOfSize:] forKeyPath:@"_placeholderLabel.font"]; 

// 转自 http://blog.csdn.net/woaifen3344/article/details/38352015