How to access a read-only propertly (re-defined readwrite in class continuation) from a derived class

Question

I am in the following scenario:

I have define a class with a property to access the activeController that i made read-only

@interface BaseViewController : UIViewController

@property (nonatomic, weak, readonly) UIViewController *activeController;

@end

In the class continuation i have define the property as readwrite as i want to be able to set the active controller only within the class:

@interface BaseViewController ()

@property (nonatomic, weak, readwrite) UIViewController *activeController;

@end

How do i make the readwrite property accessible from a derived class?

@interface ChildViewController : BaseViewController 
@end

The compiler only see the property defined as read-only in the derived class and i want to be able to make use of property within my derived class and set the activeview controller in the derived class.

Answer 1

It's better not to expose publicly an instance variable unless you really need to.

The standard pattern for making some additional parts of the class accessible to subclasses is making a separate header file, e.g. BaseViewController+Private with the declaration of readwrite. This file can then be included by 'insiders', that is class and it's subclasses.

Answer 2

You need to change the header file for BaseViewController to

@interface BaseViewController : UIViewController
{
    __weak UIViewController *_activeController;
}

@property (nonatomic, weak, readonly) UIViewController *activeController;

which will allow you to us the following class continuation in the both the base and the child

@interface ChildViewController ()

@property (nonatomic, weak, readwrite) UIViewController *activeController;

@end