Change Text Box Color using Required Field Validator. No Extender Controls Please

Question

I need to change color of TextBox whenever its required field validator is fired on Clicking the Submit button

Answer 1

You could use CustomValidator instead of RequiredFieldValidator:

.ASPX

.CS

protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)
{
    bool is_valid = TextBox1.Text != "";
    TextBox1.BackColor = is_valid ? Color.White : Color.Red;
    args.IsValid = is_valid;
}

Logic in client and server validation functions is the same, but the client function uses jQuery to access textbox value and modify its background color.