Suppose that your ASP.NET pages display contents read from database fields. Suppose also that some of those fields may contain URLs or email addresses. A typical example is when you display user information such as the email address or the personal Web site. By using regular expressions, you can automatically detect hyperlink-sensitive text and automatically wrap them into element pointing to the same URL. Let's see how to proceed. The idea is preprocessing any displayable text using ad hoc regular expressions to identify portions of text that are email addresses or Web site URLs.
You create a RegEx object and initialize it with the regular expression. Next, you call IsMatch on the input string to see whether at least one match is found. Next, you call the method Replace. Replace takes the input as its first argument. It also takes a second argument being a delegate function with the following prototype:
Function MatchEvaluator(ByVal m As Match) As String
When invoked, your callback function receives a Match object in which the Value property is set to a substring excerpted from the text. It goes without saying that substring is a portion of the original text that matches the pattern. The match evaluator creates a new string as appropriate and returns that to the caller. The Replace method ensured that the returned string replaces the match string for each occurrence.
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