This happened to me recently. I needed a way of highlighting keywords in a chunk of HTML for when users visited the site through Google. In this way, you can help your users locate the information they’ve searched for in Google quickly.
However, a simple string.Replace function wouldn’t cut the mustard. Obviously, it would also replace any mention of a keyword in the HTML markup too, and so would kill links or images.
For example, take the keyword “sitepoint” and I wish to replace it with some HTML “sitepoint“. If my image name had “sitepoint” in it, I’d end up with sitepoint.jpg”>. Not what I want.
So, I hacked together a little function to first remove all the HTML tags in a string, and then replace them once the replacement has been made. I hope it is of some use, fellow readers:
private string highlightText(string text, string keyword, string highlightColour) {
//ok strip the tags, but keep them safe
System.Collections.ArrayList a = new
System.Collections.ArrayList();
string temp = text;
//ok, find an <
while (temp.IndexOf("<") != -1)
{
int start = temp.IndexOf("<");
int end = temp.IndexOf(">");
//ok. remove
a.Add(temp.Substring(start,end-start+1));
temp = temp.Substring(0,start)+"¬"+temp.Substring(end+1);
}
//ok. string has no html now
string body = temp.Replace(keyword,""+keyword+"");
string keyUp = keyword.Substring(0,1).ToUpper()+keyword.Substring(1,keyword.Length-1);
if (keyUp != keyword)
{
body = body.Replace(keyUp,""+keyUp+"");
}
//right. re-insert the tags
while (body.IndexOf("¬") != -1)
{
int pos = body.IndexOf("¬");
body = body.Remove(pos,1);
body = body.Insert(pos,(string)a[0]);
a.RemoveAt(0);
}
return body;
}
It’s not optmised, and it isn’t pretty, but tinker and expand upon it at your will :)
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A shorter way of doing this is with a regular expression replacement tool that supports callbacks – i.e one that lets you find a certain pattern and replace it with the return value of a function that takes the matched pattern. You can see an example of the technique using PHP here:
http://simon.incutio.com/archive/2003/09/20/pirateCode
The same technique can also be used in Python and Javascript. I’ve never used .NET but from glancing over the docs it looks like the Regex.Replace(String, MatchEvaluator) method would do the job.
March 24th, 2004 at 12:40 am
Ah yes. You’d need to use the MatchCollection I believe from a regular expression and process it accordingly.
Regular expressions have always confused me to be honest…they’re so pretty yet ugly at the same time :)
March 24th, 2004 at 7:46 am
I reckon Harry Potter would be into regular expressions. Concoct some obscure incantation, unleash it, and it does something very cool but slightly scary. Definitely a dark art.
March 25th, 2004 at 2:27 am
THank You, We Got the Solution with your Article what we were searching thanks a lot.
July 2nd, 2005 at 4:27 am
using System.Text.RegularExpressions; ... public static string RemoveHTML(string in_HTML) { return Server.HtmlDecode(Regex.Replace(in_HTML, "", "")); }if not in HTTP Context page, then use the fully qualified reference System.Web.HttpContext.Current.Server.HtmlDecode if this function is in a class file rather than a page, usercontrol etc.
April 21st, 2008 at 12:57 am