Question

I’m working on an app that takes an article (simple HTML page), and a list of vocabulary terms (each may be a word, a phrase, or even a sentence), and creates a link for each term it finds. The problem is that for larger texts with more terms it takes a long time. Currently we are dealing with this by initially displaying the unmarked text, processing the links in the background, and finally reloading the web view when processing finishes. Still, it can take a while and some of our users are not happy with it.

Right now the app uses a simple loop on the terms, doing a replacement in the HTML. Basically:

for (int i=0; i<terms.count; i++){
    NSString *term = [terms objectAtIndex:i];
    NSString *replaceString = [NSString stringWithFormat:@"<a href="myUrl:\\%d>%@</a>", i, term];
    htmlString = [htmlString stringByReplacingOccurrencesOfString:term 
                                                       withString:replaceString 
                                                          options:NSCaseInsensitiveSearch 
                                                            range:NSMakeRange(0, [htmlString length] )];
}

However, we are dealing with multiple languages, so there is not just one replacement per term, but twenty! That’s because we have to deal with punctuation at the beginning (upside-down question marks in Spanish) and end of each term. We have to replace "term", "term.", and "term?" with an appropriate hyperlink.

Is there a more efficient method I could use to get this HTML marked up?

I need to keep the index of the original term so that it can be retrieved later when the user clicks the link.

Answer 1

You could process the text as follows:

1. Instead of looping over the vocabluary, split the text into words and look up each word in the vocabluary.

2. Create some index, hash table or dictionary to make the lookup efficient.

3. Don’t use stringByReplacingOccurrencesOfString. Each time it’s called it makes a copy of the whole text and won’t release the memory until the autopool is drained. (Interestingly, you haven’t run into memory problems yet.) Instead use a NSMutableString instance where you append each word (and the characters between them), either as it was in the original text or decorated as a link.