Hi,

I use the multiform to make an form with several steps, but in 1 step I want to make that when the checkbox is checked there will be
several new fields shown for input.

Bit of the code:
new CheckboxsetField($name ='Voogd2', $title = 'Voer eventueel een 2e persoon in', $source = array('Toevoegen' => Toevoegen')),

new LabelField($name = 'Persoonsgegevens2', $title = '<strong><br/>Persoonsgegevens<br/><br/></strong>', null, true),
new TextField('Voornaam2', 'Voornaam'),
new TextField('Achternaam2', 'Achternaam'),

So when the checkbox is checked, show the labelfield en textfields.

See entire code below.

Suzanne

To do any show/hide logic you have to use javascript. Lots of javascript tutorials on the web (e.g http://iamzed.com/2006/12/14/using-jquery-to-show-hide-form-elements-based-on-a-checkbox-selection/)

There's thread here showing how to use JavaScript with SilverStripe to hide / display form fields:

http://www.silverstripe.org/archive/show/3138