Change your performDragOperation: method to this:
- (BOOL)performDragOperation:(id<NSDraggingInfo>)sender {
NSPasteboard *pboard = [sender draggingPasteboard];
if ([[pboard types] containsObject:NSURLPboardType]) {
NSArray *urls = [pboard readObjectsForClasses:@[[NSURL class]] options:nil];
NSLog(@"URLs are: %@", urls);
}
return YES;
}