Overridden properties from superclass - iphone

Question

I have a superclass of UIViewController - MasterViewController which declares a property called itemsViewController. This declares a method called from the MasterViewController, and is wired up via a storyboard in IB.
I have a subclass of MasterViewController which redeclares this property as a specific iPad version, but I can't access the redeclared property from the parent class.
MasterViewController
#interface MasterViewController : UIViewController {
}
#property (nonatomic, strong) IBOutlet ItemsViewController *itemsViewController;
#end
#implementation MasterViewController
#synthesize itemsViewController;
-(void)viewDidLoad {
// I can access itemsViewController in viewDidLoad.
}
#end
MasterViewController_iPad
#interface MasterViewController_iPad : MasterViewController {
IBOutlet ItemsViewController_iPad *_itemsViewController;
}
#property (nonatomic, strong) IBOutlet ItemsViewController_iPad *itemsViewController;
#end
#implementation MasterViewController_iPad
#synthesize itemsViewController = _itemsViewController;
-(void)viewDidLoad {
[super viewDidLoad];
// when I call super viewDidLoad, itemsViewController is nil, as though the property hasn't been overriden
// _itemsViewController is not nil in viewDidLoad.
}
#end
Am I misunderstanding the way property inheritance works in Objective-C?

Answer 1

You can't change the type signature of a method when you override a superclass method.
MasterViewController has these methods:
(void)setItemsViewController:(ItemsViewController *)foo
(ItemsViewController *)itemsViewController
But you're trying to give MasterViewController_iPad these methods:
(void)setItemsViewController:(ItemsViewController_iPad *)foo
(ItemsViewController_iPad *)itemsViewController
Which you can't do: you can't overload the same method name but have different types for the arguments.
If ItemsViewController_iPad is a subclass of ItemsViewController, a quick solution would be to keep the same signature as in MasterViewController but simply use an ItemsViewController_iPad when you set the property.

Answer 2

You can use category if you'd like to override property. Here is example:
I have PDFFileChooserViewController with PDFFileModel and PDFFilesDataSource and some logic related to this properties.
#class PDFFileModel, PDFFilesDataSource;
#interface PDFFileChooserViewController : UIViewController
#property (nonatomic, strong) PDFFileModel* selectedModel;
#property (nonatomic, strong) PDFFilesDataSource*dataSource;
#end
Then I'd like to add specific ViewController for choosing files from Dropbox but my model have some additional fields for example dropboxPath and my DropboxDataSource gets files using another way. So I decided to create category and override this properties:
#import "PDFFileChooserViewController.h"
#class DropboxFileModel,DropboxDataSource;
#interface DropboxViewController : PDFFileChooserViewController
#end
#interface DropboxViewController (ModelCategory)
#property(nonatomic, strong) DropboxFileModel* selectedModel;
#property(nonatomic, strong) DropboxDataSource* dataSource;
#end
Notice that this category will be visible inside DropboxViewController only where I can manipulate with that properties but another classes see only super class interface