[TYPO3-seminars] Using modifyListItem hook: getLinkToUnregistrationPage() doesn't work

[Michael Spindler]

Hello list,

at first I have to thank the seminar manager programming team for the 
excellent and well structured extension!

For customizing purposes I have to create a "compact" 
seminar-plus-registration list (maybe this also could be a new 
"what_to_display" case). So I use a list of type "My VIP events" in the 
frontend. All attendants are VIPs and may see other registrations for a 
seminar.

By using the modifyListItem hook I replace the list_registrations marker 
(that's the link to the list of registered attendants) by the attendants 
list directly (for getting the list without a second click). That works 
fine.

Also registering for a seminar is possible by using the 
getRegistrationLink() method. Therefore I set the second parameter to 
$parent->getSeminar().

Now the problem is the unregistration link: I tried using 
getLinkToUnregistrationPage() but the second parameter, 
tx_seminars_registration $registration which I set by calling 
$parent->getRegistration() always returns NULL. How can I get a 
registration to a seminar to create the link?

This is the code I use in my own extension:

-------------------------------------------------
class tx_msseminarsxtender_modlistitem {

     function modifyListItem(tx_seminars_pi1 $parent) {

	// create the list of attendants
	$registrationsList = tx_oelib_ObjectFactory::make(
		'tx_seminars_pi1_frontEndRegistrationsList',
		$parent->conf,
		'list_vip_registrations',
		$parent->getSeminar()->getUid(),
		$parent->cObj);

	$result = $registrationsList->render();
	$registrationsList->__destruct();
	unset($registrationsList);

	// Link for unregistering for a seminar
	$unregistrationLink = '';
	if ($parent->getRegistration()) { // <-- always returns NULL!
		$unregistrationLink =
		(($parent->getSeminar()->isUnregistrationPossible()) ?
			
$parent->getRegistrationManager()->getLinkToUnregistrationPage($parent, 
$parent->getRegistration()) : '');
	}

	// Link for registering for a seminar
	$registrationLink = 
$parent->getRegistrationManager()->getRegistrationLink($parent, 
$parent->getSeminar());

	// replace marker
	$parent->setMarker('list_registrations', $result . $unregistrationLink 
. $registrationLink);

     }

}
-------------------------------------------------

And this is how It should look like (logged in as "Albert Maier):

Seminar	             Registrations  EMail       register/unregister link

30.11.2010, 10:00    Albert Maier   am at mail.de	unregister

30.11.2010, 11:00    Simon Schüler  sis at mail.de	
                      Albert Maier   am at mail.de  unregister

30.11.2010, 12:00                               register


Any hints would be helpful...

Greetings,
Michael.