Some sample checkbox form elements:

Let's check out our values just submitted:

FYI: Note that the above form submits back to this same page. If you haven't yet submit the form then there won't be any values in the text below since they are retrieved from the form. In this case, the values reflected are simply the defaults and are the same results you would get if you submitted the form without checking anything.

The Default No-Frills Checkbox

By default, an HTML checkbox element returns nothing if it wasn't checked and a value of "on" if it was. So by checking it's value we can determine if it was checked or not when the form was submitted. The No-Frills Checkbox was: Not Checked .

Checkbox With An Associated Value

If you don't like the fact that the checkbox returns the value of "on" it's really easy to change. Simply add a value parameter and assign to it what you'd like the value returned by the checkbox to be. The Checkbox With An Associated Value returned: .

Multiple Checkboxs With The Same Name

Probably one of the most useful uses of the checkbox is to allow users to check multiple selections. Instead of having to chech each box's status individually you can simply name them all the same and the results will be returned in a convenient collection like fashion.

You can access them in a number of ways. First you can use the "For Each" syntax illustrated here (in the source code at least): .

Along the same lines you can access them by index: .

And perhaps the easiest way is to just get them as a comma delimited list: .

Checkbox Which Maintains It's State

At this point there's really nothing different about this checkbox from any other, but I thought I should illustrate the technique when building the form (see the form generating section of the source code) because it's so useful in real life. In particular, when you're sending a user back to the form to check their entries, it's really frustrating for them if they have to re-enter all their values and re-check all the boxes.

In terms of the value, like I said, this is just like the standard checkbox, but just to keep up the pattern... Checkbox Which Maintains It's State returned: .

Checkboxes are probably one of the two most confusing HTML form elements. Dealing with them via ASP isn't hard, but it can get confusing. Hopefully this will help clear things up for you.

Note that I've used "Get" for the form so that you can see the form data being transferred on the QueryString. I thought that it might help you keep track of what's actually being sent back to the server and understand the checkbox operation a little better.

Because of their similarity, if you haven't already seen it, you should probably check out our radio button sample as well.