Sometimes technical, sometimes not, never a kitty

This article came up on the news today: Allowing Only Numbers in ASP.NET Textboxes.  In this article, Bipin uses a custom validator to enforce input.  I usually like Bipin's ideas, but this one seems to be a little more difficult than it needs to be.

I think there's a better way to do this--use a regular expression validator.  To test this, create a page, and add a textbox, regular expression validator, and a button.  For the validation expression, enter the following:

^[0-9]+$

Compile your page and test with some diffrerent inputs.

A quick explanation of the expression:
^ indicates the start of the input
[0-9] indicates a range of allowable characters.  You could do [0,1,2,3,4,5,6,7,8,9], but that's not lazy.
+ indicates 'match preceeding one or more times'
$ indicates the end of input

If you wanted to enforce a length of input, you could do something like:

^[0-9]{6,12}$

which would enforce a minimum of 6 characters and a max of 12.

I think regular expressions are too often overlooked, but they're very powerful and simple once you work with them a little bit.  For a good basic overview of regular expressions, check out

The Web Professional's Handbook

And a more in-depth RegEx reference in:

Pure JavaScript: 2nd Ed. (an absolute steal if you buy it used)

Regular Expressions with .NET [DOWNLOAD: PDF]

Downloadable e-bok in PDF format, from Amazon.

Mastering Regular Expressions, Second Edition (The Owl Book)

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Thinking about Joseph's comments below, one could extend Bipin's idea and use a regular expression instead of parsing the string and checking to see if each character is numberic or a period.  You could also add in a check to see if the field was blank, and save on the second validator.

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