title: What does the "Couldn't compile connection:" error mean?
body: <p>I'm getting the following error from Xcode:</p>
  
  <pre><code>Couldn't compile connection: &lt;IBCocoaTouchOutletConnection:0x401538380
  &lt;IBProxyObject: 0x40154a260&gt; =&gt; categoryPicker =&gt; &lt;IBUIPickerView: 0x4016de1e0&gt;&gt;
  </code></pre>
  
  <p>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:</p>
  
  <pre><code>@interface FiltersTableViewController : UITableViewController &lt;UIPickerViewDataSource, UIPickerViewDelegate&gt; {
      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
  </code></pre>
  
  <p>The UIPickerView is in a UITableViewCell.  Here's an image of the storyboard, the connection from "categoryPicker" to "FiltersTableViewController" causes the error:
  <img src="https://i.stack.imgur.com/DG4bV.png" alt="enter image description here"></p>
  
  <p>Thanks for any ideas, or suggestions on how to debug it!</p>
  
  <p>EDIT:
  I removed the connection and added one line to numberOfComponentsInPickerView:</p>
  
  <pre><code>- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
  
      categoryPicker = pickerView;
  
      return 1;
  </code></pre>
  
  <p>}</p>
  
  <p>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.</p>
  
  <p>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.</p>