I have been trying to add a file manager to the image gallery so that my client can link files to an album in the same way that images get linked to an album.
I have gotten it to the point where my image resource is linked to the imagegallerypage and to an imagegalleryalbum, adding files to different albums works but I can't use the filter the way you do in the imagegallerymanager.
I stole the lines
$manager->setFilter('AlbumID','Choose an album', $this->Albums()->toDropdownMap('ID','AlbumName'));
if($this->Albums()->Count() > 0)
$manager->filter = "AlbumID_".$this->Albums()->First()->ID;
but the last line that sets the filter property makes the page load fail. The error I get is "Missing argument 2 for DataObjectManager::setFilter()".
Everything works if I add $this->Albums()->First()->ID as the last argument to setFilter() so I have no idea why it fails when I add it the way you do in the ImageGalleryManager.