ios - Replace UITextViews text with attributed string

Question

I have a UITextView and when the user is entering text into it, I want to format the text on the fly. Something like syntax highlighting...

For that I'd like to use UITextView...

Everything works fine expect one problem: I take the text from the text view and make an NSAttributedString from of it. I make some edits to this attributed string and set it back as the textView.attributedText.

This happens everytime the user types. So I have to remember the selectedTextRange before the edit to the attributedText and set it back afterwards so that the user can continue typing at the place he was typing before. The only problem is that once the text is long enough to require scrolling, the UITextView will now start scrolling to the top if I type slowly.

Here is some sample code:

- (void)formatTextInTextView:(UITextView *)textView
{
  NSRange selectedRange = textView.selectedRange;
  NSString *text = textView.text;

  // This will give me an attributedString with the base text-style
  NSMutableAttributedString *attributedString = [self attributedStringFromString:text];

  NSError *error = nil;
  NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"#(\w+)" options:0 error:&error];
  NSArray *matches = [regex matchesInString:text
                                    options:0
                                      range:NSMakeRange(0, text.length)];

  for (NSTextCheckingResult *match in matches)
  {
    NSRange matchRange = [match rangeAtIndex:0];
    [attributedString addAttribute:NSForegroundColorAttributeName
                             value:[UIColor redColor]
                             range:matchRange];
  }

  textView.attributedText = attributedString;
  textView.selectedRange = selectedRange;
}

Is there any solution without using CoreText directly? I like the UITextViews ability to select text and so on....

Answer 1

I am not sure that this is correct solution, but it works.
Just disable scrolling before formatting text and enable it after formatting

- (void)formatTextInTextView:(UITextView *)textView
{
    textView.scrollEnabled = NO;
    NSRange selectedRange = textView.selectedRange;
    NSString *text = textView.text;

    // This will give me an attributedString with the base text-style
    NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithString:text];

    NSError *error = nil;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"#(\w+)" options:0 error:&error];
    NSArray *matches = [regex matchesInString:text
                                      options:0
                                        range:NSMakeRange(0, text.length)];

    for (NSTextCheckingResult *match in matches)
    {
        NSRange matchRange = [match rangeAtIndex:0];
        [attributedString addAttribute:NSForegroundColorAttributeName
                                 value:[UIColor redColor]
                                 range:matchRange];
    }

    textView.attributedText = attributedString;
    textView.selectedRange = selectedRange;
    textView.scrollEnabled = YES;
}