Replace UITextViews text with attributed string

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;
}

Used Sergeys's answer myself and ported it to Swift 2:

func formatTextInTextView(textView: UITextView) {
    textView.scrollEnabled = false
    let selectedRange = textView.selectedRange
    let text = textView.text

    // This will give me an attributedString with the base text-style
    let attributedString = NSMutableAttributedString(string: text)

    let regex = try? NSRegularExpression(pattern: "#(\\w+)", options: [])
    let matches = regex!.matchesInString(text, options: [], range: NSMakeRange(0, text.characters.count))

    for match in matches {
        let matchRange = match.rangeAtIndex(0)
        attributedString.addAttribute(NSForegroundColorAttributeName, value: UIColor.redColor(), range: matchRange)
    }

    textView.attributedText = attributedString
    textView.selectedRange = selectedRange
    textView.scrollEnabled = true
}