Question

I’m working with NSRegularExpression to read a text and find out hashtag.
This is NSString that I used in regularExpressionWithPattern.

- (NSString *)hashtagRegex
{
    return @"#((?:[A-Za-z0-9-_]*))";
    //return @"#{1}([A-Za-z0-9-_]{2,})";

}

And this is my method:

 // Handle Twitter Hashtags
  detector = [NSRegularExpression regularExpressionWithPattern:[self hashtagRegex] options:0 error:&error];
  links = [detector matchesInString:theText options:0 range:NSMakeRange(0, theText.length)];
  current = [NSMutableArray arrayWithArray:links];

    NSString *hashtagURL =   @"http://twitter.com/search?q=%23";
  //hashtagURL = [hashtagURL stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding];

  for ( int i = 0; i < [links count]; i++ ) {

    NSTextCheckingResult *cr = [current objectAtIndex:i];

    NSString *url = [theText substringWithRange:cr.range];

    NSString *nohashURL = [url stringByReplacingOccurrencesOfString:@"#" withString:@""];
    nohashURL = [nohashURL stringByReplacingOccurrencesOfString:@" " withString:@""];

    [theText replaceOccurrencesOfString:url 
                             withString:[NSString stringWithFormat:@"<a href=\"%@%@\">%@</a>", hashtagURL, nohashURL, url]
                                options:NSLiteralSearch 
                                  range:NSMakeRange(0, theText.length)];
    current = [NSMutableArray arrayWithArray:[detector matchesInString:theText options:0 range:NSMakeRange(0, theText.length)]];

  }

  [theText replaceOccurrencesOfString:@"\n" withString:@"<br />" options:NSLiteralSearch range:NSMakeRange(0, theText.length)];

  [_aWebView loadHTMLString:[self embedHTMLWithFontName:[self fontName] 
                                                   size:[self fontSize] 
                                                   text:theText]
                    baseURL:nil];

Everything worked but it figured out a little issue when I use a string like this:

NSString * theText = @"#twitter #twitterapp #twittertag";

My code highlights only #twitter on each word and not the second part of it (#twitter #twitter(app) #twitter(tag)).
I hope someone will help me!

Thank you 🙂

Answer 1

The statement

[theText replaceOccurrencesOfString:url 
                         withString:[NSString stringWithFormat:@"<a href=\"%@%@\">%@</a>", hashtagURL, nohashURL, url]
                            options:NSLiteralSearch 
                              range:NSMakeRange(0, theText.length)];

is replacing all instances of the string url with the replacement string. In the example you give, the first time through the loop, url is @"#twitter", and all three occurrences of that string within theText are replaced in one go. This is what theText looks like then:

<a href="http://twitter.com/search?q=%23twitter">#twitter</a> <a href="http://twitter.com/search?q=%23twitter">#twitter</a>app <a href="http://twitter.com/search?q=%23twitter">#twitter</a>tag

So, of course, the next two times round the loop, the results are not quite what you expect… !

I think the fix is to limit the range of the replacement:

[theText replaceOccurrencesOfString:url 
                         withString:[NSString stringWithFormat:@"<a href=\"%@%@\">%@</a>", hashtagURL, nohashURL, url]
                            options:NSLiteralSearch 
                              range:cr.range];