build a regex to search underlined text

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Iam having a trouble implementing a certain technique - selecting next text in a richtextbox control which is underlined.

You see iam trying to make a word processor but am stuck. I have been able to write the code to select each word one-by-one on pressing F1. Now i want to select only those words which are underlined but can be a phrase rather than single word.

Eg: hello codeproject.com - this is a nice site for everyone

imagine my cursor is at beginning (before hello) and i press F1 (or any button) I want to select "this is a" and on next keypress "site for". But iam not being able to build a regex or implement simple logic for this requirement.

Any help plz? (Any language will do -vb.net / C#)

Posted 19-Apr-11 23:24pm

amit_upadhyay

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OriginalGriff · Answer 1 · 2011-04-19T23:34:00

Solution 1

Run myRichTextBox.Rtf through this:

//  using System.Text.RegularExpressions;
public static Regex regex = new Regex("(?<=\\\\\\\\ul).*(?=\\\\\\\\ulnone)",
    RegexOptions.IgnoreCase
    | RegexOptions.Multiline
    | RegexOptions.CultureInvariant
    | RegexOptions.IgnorePatternWhitespace
    | RegexOptions.Compiled
    );

Posted 19-Apr-11 23:34pm

OriginalGriff

Comments

BobJanova 20-Apr-11 7:44am

That won't if the RTF does it this way
Here is some {\ul underlined text} in a group

That's the problem with RTF, there are too many ways to do things so it is hard to work with.

Your solution will work with what the current version of the RTF control does when you press the U button, but it won't necessarily work with loaded documents or code-generated RTF snippets.

(Also, surely it would be better to use @ strings for all those backslashes? @"(?<=\\\\ul).*(?=\\\\ulnone)")

Finally, if the user wants to select the underlined text, shouldn't the '.*' be in a bracketed group?

OriginalGriff 20-Apr-11 8:10am

There are, so you would have to create a regex to handle them as well - stupid specification :laugh: My solution was based on rtf code generates by the using an underlined font to writ ethe text, so it should work for a standard RichTextBox control.
As regards the multiple slashes, I used Expresso to generate and test teh regex, so it was it's choice to not use the @ string prefix! I wasn't about to remove half of them and potential create a problem by counting wrong...
Because the regex uses excluded prefix and suffix groups, you shouldn't need to group the actual content: it should work as is.

BobJanova 20-Apr-11 13:19pm

Oh, that's what that syntax in the regex is doing :P. I must say, I would write it as
@"\\\\ul(.*)\\\\ulnone"
(Actually, isn't that still too many backslashes? I think it should only be 2 after escaping.)

Because groups can be nested, you have to count braces in the latter case. I'm not sure a regex can even do that.

OriginalGriff 20-Apr-11 14:14pm

No, because you are double escaping: you need to match the text @"\\ul" for start or end of underlining, but '\' is a special in the regex as well, so it needs escaping there also to get a pair of '\' characters into the match string.

BobJanova 20-Apr-11 14:31pm

RTF only uses single backslashes (@"\ul stuff \ulnone") though. I don't get where the extra level of escape is coming from.

OriginalGriff 21-Apr-11 4:56am

It comes from CBF: Complete Brain Failure on my part. For no obvious reason, I copy and pasted the RTF direct from the debugger into Expresso, and looked at it there with out thinking "VS always doubles escape characters so you can see them". :blush:
It's been years since I last did that!

Chris Trelawny-Ross 20-Apr-11 20:19pm

Bobjanova is right - RTF only uses single backslashes. The following expression works to match a an underlined passage in RTF with ONLY ONE UNDERLINED PASSAGE - but it does not falsely trigger on \ul or \ulnone in the 'real text': (?<=(?<!\\)\\ul ).*(?=(?<!\\)\\ulnone). (The nested '(?<!\\)' expression rejects the '\' that escapes the '\' in the 'real' text.

Unfortunately, this breaks if there are more than one underlined passage in the RTF. However, this can be remediated by performing a second regex pass on the matched text, capturing only the text preceeding the first '\ulnone' (if any).