UITextView 文本居中时突出显示

Question

我使用以下代码突出显示我UITextView的文本 - 每次文本更改时，我将其转换为NSMutableAttributedString以便我可以将其居中，添加突出显示并设置字体。

创建 UITextView

UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(40, 40, 300, 100)];
textView.center = self.view.center;
textView.font = [UIFont fontWithName:@"RopaSans-Italic" size:30];
textView.backgroundColor = [UIColor clearColor];
textView.textColor = [UIColor whiteColor];
textView.textAlignment = NSTextAlignmentCenter;
textView.text = [@"" uppercaseString];
textView.delegate = self;
[self.view addSubview:textView];

委托方法

-(void)textViewDidChange:(UITextView *)textView{

    textView.text = [textView.text uppercaseString];
    NSString *string = textView.text;

    NSMutableAttributedString *att = [[NSMutableAttributedString alloc] initWithString:textView.text];
    NSMutableParagraphStyle *paragrapStyle = [[NSMutableParagraphStyle alloc] init];
    paragrapStyle.alignment = NSTextAlignmentCenter;
    paragrapStyle.lineBreakMode = NSLineBreakByWordWrapping;

    [att addAttribute:NSParagraphStyleAttributeName value:paragrapStyle range:[textView.text rangeOfString:textView.text]];
    [att addAttribute:NSBackgroundColorAttributeName value:[UIColor redColor] range:[textView.text rangeOfString:textView.text]];
    [att addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"RopaSans-Italic" size:30] range:[textView.text rangeOfString:textView.text]];
    [att addAttribute:NSForegroundColorAttributeName value:[UIColor whiteColor] range:[textView.text rangeOfString:textView.text]];

    //Find all occurencies of newline
    NSString *substring = @"\n";
    NSRange searchRange = NSMakeRange(0,string.length);
    NSRange foundRange;
    while (searchRange.location < string.length) {
        searchRange.length = string.length-searchRange.location;
        foundRange = [string rangeOfString:substring options:nil range:searchRange];
        if (foundRange.location != NSNotFound) {

            [att addAttribute:NSBackgroundColorAttributeName value:[UIColor clearColor] range:foundRange];

            searchRange.location = foundRange.location+foundRange.length;
        } else {
            break;
        }
    }

    textView.attributedText = att;

}

但是，当文本开始太长而无法放入UITextView并且光标跳到下一行时，即使那里没有文本，背景也会着色（参见图 1）。当用户按下回车键并跳到下一行时，也会发生同样的情况（见图 1）。但是，我能够通过查找字符串中所有 \n 字符的范围并将NSBackgroundColorAttributeName该范围的[UIColor clearColor]. 效果如图 2 所示。我尝试对所有换行符（\r 和 \r\n）执行相同的操作，但是它不起作用，所以我现在坚持使用 a UITextView，它有点作用我想要除非用户不使用“Enter”跳到下一行。

我怎样才能解决这个问题？