If this parameter is needed for initializing your form then you could do it like this (keep in mind that you should always validate user input)
public function executeNew($request)
{
$formOptions = array('parameter' => $request->getParameter('parameter'));
$this->form = new MyForm(array(), $formOptions);
// Then within your form you access it with:
// $parameter = $this->options['parameter'];
// or even better:
// $parameter = $this->getOption('parameter');
... more code ...
}
If the parameter is submitted as part of the form then you should bind it like this:
public function executeNew($request)
{
$this->form = new MyForm();
if ( $request->isMethod('post') ) {
$this->form->bind($request->getPostParameters());
}
... more code ...
}
Please refer to the Symfony's Forms in Action for more on how to create and use forms.
Edit: Added $this->getOption('parameter')
to the code example.