objective c - What does the "Couldn't compile connection:" error mean?

Question

I'm getting the following error from Xcode:

Couldn't compile connection: <IBCocoaTouchOutletConnection:0x401538380
<IBProxyObject: 0x40154a260> => categoryPicker => <IBUIPickerView: 0x4016de1e0>>

I've narrowed this down to a single outlet connection in storyboard. My code (about 30 views with lots of other connections) compiles and runs fine until I add a connection from a UIPicker to the view's categoryPicker property. The picker itself also works fine, I just can't reload it without getting this connection to work:

@interface FiltersTableViewController : UITableViewController <UIPickerViewDataSource, UIPickerViewDelegate> {
    NSFetchedResultsController *fetchedResultsController;
    FilterTableViewController *filterView;

    AppDelegate *appDelegate;
    NSManagedObjectContext *managedObjectContext;       
}

@property (nonatomic, strong) FilterTableViewController *filterView;
@property (nonatomic, strong) NSFetchedResultsController *fetchedResultsController;
@property (nonatomic, strong) NSManagedObjectContext *managedObjectContext;

@property (nonatomic, weak) IBOutlet UIPickerView *categoryPicker;

- (void)configureCell:(FilterTableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
- (void)performFetch;

@end

The UIPickerView is in a UITableViewCell. Here's an image of the storyboard, the connection from "categoryPicker" to "FiltersTableViewController" causes the error:

Thanks for any ideas, or suggestions on how to debug it!

EDIT: I removed the connection and added one line to numberOfComponentsInPickerView:

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {

    categoryPicker = pickerView;

    return 1;

}

This now works!, but I'd like to understand why the connection won't work and what that error message means. Right now this seems like a kludge to me since I use IB connections everywhere else to get object references.

EDIT 2: Connecting a prototype cell generates this error: Illegal Configuration: Connection "Cell" cannot have a prototype object as its destination. Not sure if this is new in Xcode 4.5.

Answer 1

The problem is that this is a prototype cell. It is meaningless to have an outlet to something in it, because it isn't a real cell: it's a model for what might be dozens or hundreds of cells, and which one would the outlet point to in that case?