Hello Uncle Cheese,
thank you for your answer, this works perfect. Ma next Problem ist that I have subclassed the CalendarDateTime class, in order to get my own fields in there. This CalendarDateTime class also has a Category field, which I would like to have in the filter. So I have added the field to the filter in the Holder class:
$fields->addFilterField(new DropdownField('LineDanceDateTime_Category', 'Kategorie', singleton('LineDanceDateTime')->dbObject('Category')->enumValues()));
The filter now shows up correctly, but the problem is when I apply the filter, the resulting sql command tries to load from the table LineDanceDateTime_Live and this does not exist.
And last but not least: Is it possible to get a detail page for announcements too? The Problem ist, that I think its really unhandy to create an event for each appointment I have. I think these are only good for recurring events. But I have about 10 to 20 "announcements" per month, which only need a start date and an end date. But I'd really like to have a detail page....
Is this possible somehow?