Question

I have some local HTML and CSS that I display using a UIWebview. I want to incorporate search hit highlighting.

Here is my highlighting method:

-(void) highlightsSearchTerm:(NSString *)searchTerm
{
    NSString *highlightedSearchTerm = [NSString stringWithFormat:@"<span class='highlight'>%@</span>",searchTerm];

    NSString *highlightedArticle = [article.articleHTML stringByReplacingOccurrencesOfString:searchTerm withString:highlightedSearchTerm options:NSCaseInsensitiveSearch range:NSMakeRange(0, [article.articleHTML length])];

    article.articleHTML = highlightedArticle;
}

The issue with this is that it replaces, for example, Obama with the user’s search query, which might have been obama (note the case). I want to maintain the case of the original article while incorporating the hit highlighting.

I’m hoping for a more elegant solution than manually finding the starting and ending indexes of each hit term and then inserting <span class="highlights"> and ” respectively.

Basically I want something like:

+ [NSString stringByWrappingExistingString:(NSString *)stringToWrap withString:(NSString *)wrappingString options:NSCaseInsensitiveCompare];

Any thoughts?

Answer 1

You can use NSRegularExpression to do this (code typed in directly, check for errors):

NSRegularExpression *re = [NSRegularExpression regularExpressionWithPattern:@"Obama" 
                                                                    options:NSRegularExpressionCaseInsensitive
                                                                      error:NULL];
NSString *output = [re stringByReplacingMatchesInString:inputString
                                                options:0
                                                  range:NSMakeRange(0, inputString.length)
                                           withTemplate:@"<span class='highlight'>$0</span>"];

The regular expression search string, @"Obama", is straightforward in this case as you are looking for a literal match; the option options:NSRegularExpressionCaseInsensitive makes the match case-insensitive.

While the example uses a literal Obama you can obviously construct the string dynamically; however be careful in that case about using strings which contain regular expression meta-characters, they will need to be escaped.

The replace template contains $0 which will be replaced by what was matched (exactly, so preserving case).