[TYPO3-Solr] ViewHelper

[Heiko Kromm | Paints]

Hi list, 

is it possible to create own ViewHelpers? 
I want to add a daterange to the searchbox and would like to use a viewhelper there. 

Therefore I created my own extension and created a viewhelper in it, which implements the tx_solr_ViewHelper. 
The viewhelper ist loaded with ext_autoload.php. 
But if the template calls my ViewHelper I get a exeption: 
: exception 't3lib_error_Exception' with message 'PHP Catchable Fatal Error: Argument 1 passed to tx_solr_Template::renderMarkerViewHelper() must implement interface tx_solr_ViewHelper, null given, called in /typo3conf/ext/solr/classes/class.tx_solr_template.php on line 325 

Thanks 
Heiko