ASP.NET: Writing a custom server-side-only validator

Question

I want to write a custom validator which doesn't do anything before the user makes a post back (i.e. no JavaScript will be generated for it). The validator should make sure that there is a POST argument with the name hello. The value of that argument must be a comma-separated string of integers.

The reason that I want to make this an actual validator is that I want to integrate the error message into the validation summary that I'm using, which displays a bulleted list of errors.

So where do I start?

Mike J · Accepted Answer · 2009-10-29 18:14:22Z

2

First, add a custom validator control to the page

<asp:CustomValidator ID="MyValidator" runat="server" ErrorMessage="My error message" 
    OnServerValidate="MyValidator_OnServerValidate" />

Then in your codebehind add the MyValidator_OnServerValidate method.

protected void MyValidator_OnServerValidate(object sender, ServerValidateEventArgs e)
{
      e.IsValid = false;

      // Validation logic goes here
      if(Request.Form["hello"] == null)
          return;

      ...

      // If we have made it this far, then everything is valid
      e.IsValid = true;
}

edited Oct 29, 2009 at 18:14

answered Oct 29, 2009 at 18:07

Mike J

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brumScouse · Accepted Answer · 2010-08-03 06:42:45Z

0

The validation summary works with client side errors too. That is, you DONT have to postback to get the validation summary to display a new error. In fact, as a strategy, I would recommend having client script AS WELL as server side checks where possible. At the very least - when enabled - the client checking can help reduce network chatiness, server resources and improve the user experience.

answered Aug 3, 2010 at 6:42

brumScouse

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1 Comment

Deniz Dogan Over a year ago

It was a while since I asked this question, but I think the reason I said that I only wanted server-side validation was that I had a hard time understanding custom validators at all and it would be a tad simpler to explain how they work if it was supposed to be server-side only. I don't remember to be honest.

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