How To Validate A ListBox Control In to make sure it has items listed in it.

I have two listboxes on an page. The first one is a multiselect that allows the user to select specific employees.  They can then move their selected employees (via a button click) to the other listbox.  Pretty standard fare and that all works fine.   Before they click continue, I want to make sure there are employees in the second listbox and it is not empty.  How would I validate that?  Can I use a required field validator somehow or would I need a custom validator?  Please be specific.

Thanks in advance
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following code should do it:

if(listBox.Items.Count != 0)

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kenadelglassAuthor Commented:
dkloeck - I know I can do that on the button click but I would like to use the validation controls for this - Do I need to use a custom validator then or is there a way to do it with the Required field validator?
kenadelglassAuthor Commented:
It works fine. I decided to enable and disable the Continue button based on the lstBox.Items.Count rather than use the Validators.  Thanks
See for more info on validators, if you want to try out the other way sometime
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