The standard ASP.NET validator controls such as the RequiredFieldValidator or the RegularExpressionValidator do not cover all validation requirements, so usually developers tend to create a CustomValidator for such scenarios.

A major problem with the CustomValidator is reusability, as if you wanted to use the validator in another project then there would be some copying and pasting and code duplication, then you have to maintain multiple versions of the same control.

The solution, as you have guessed from the title, is to build your own validator control when possible to promote reusability.

In this post I will be showing you in three simple steps how to build an ASP.NET validator control and take credit card number format check to show by example. I will also be building the architecture so that your validator and other validators that you will develop in the future could be as reusable as possible.

How to Check a Credit Card Format

Luhn check is an algorithm that checks if a credit card number is valid (format wise), so in practice, before you even think of doing any further processing on the credit card, this check should be satisfied.

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Session expiration in ASP.NET is a nasty problem. Imagine yourself filling a long form, hitting submit then boom you get the login page! That happened to me before and probably happened to you.

This problem doesn’t have an out-of-box solution in ASP.NET and there are different appraoches to solve it.

1. Increasing the session time out. Probably you are aware of the cons of this problem which are mainly consuming more server resources.
2. Having an image or an iframe that refreshes regularly and requests the server. This approach is a per page approach and you can select the pages to implement it on.

Personally, I’ve been using the second approach for a long time and didn’t have any problem with it. However, I made it more reusable, not to mention “cleaner”, by making it a web control.

If you are just interested in using the control then you can skip to the last section “Using the Control.”

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