Access subclass property from super class - ios

Question

I have a class that extends UIViewController called HorizontalModal, which, among other things, I want to automatically generate a back button on each view that extends it. If I put the code to draw the back button in the viewDidLoad method for HorizontalModal, nothing shows up. But when I put that same code in the viewDidLoad method for the class that inherits from HorizontalModal, the button shows up fine.
E.g:
self.backButton = [[BackButton alloc] initWithFrame:CGRectMake(10, 10, 50, 50)];
[self.view addSubview:self.backButton];
Seems to me that I'm missing something about class extension and inheritance in objective C. Clearly self.view in HorizontalModal and self.view in the child class refer to two different things. So is there a way to keep that method in the HorizontalModal class, but be able to add the back button to the child class view? IE, can I access a sub-class property from a super class? Or is there a different way of doing this (maybe with categories)?
Thanks

Answer 1

If I put the code to draw the back button in the viewDidLoad method
for HorizontalModal, nothing shows up. But when I put that same code
in the viewDidLoad method for the class that inherits from
HorizontalModal, the button shows up fine.
It sounds like your subclass's -viewDidLoad isn't calling it's superclass's -viewDidLoad, like:
- (void)viewDidLoad
{
[super viewDidLoad];
// subclass-specific view setup stuff here
}
That allows the superclass's version of -viewDidLoad to do its thing first, followed by whatever the subclass needs to do.
can I access a sub-class property from a super class? Or is there a
different way of doing this (maybe with categories)?
If the superclass needs some method that every subclass is expected to provide, then you should put that method in the superclass and let subclasses override it. Normally, the subclass's implementation of the method calls the superclass's version, but if that's required then you should document that fact.
The same is true for properties: if your superclass needs to access some property of the subclass (e.g. backButton), the superclass should define that property itself. The subclass is then free to change the value of the property or even provide different property accessors, and code in the superclass that uses the property will just work. In general, the superclass shouldn't have to know anything about its subclasses.
So, to be more concrete, let's say you have MyModal, a subclass of HorizontalModal:
#interface HorizontalModal : UIViewController
#property(strong) UIView *backButton;
#end
#implementation HorizontalModal
- (void)viewDidLoad
{
self.backButton = [[BackButton alloc] initWithFrame:CGRectMake(10, 10, 50, 50)];
[self.view addSubview:self.backButton];
}
#end
#interface MyModal : HorizontalModal
//...
#end
#implementation MyModal
- (void)viewDidLoad
{
[super viewDidLoad];
// more code specific to MyModal's view hierarchy
}
#end
Now the -viewDidLoad method of HorizontalModal will be able to access the backButton property, even if MyModal has changed the value of the property or overridden the accessors. Remember that self points to the exact same object in both versions of -viewDidLoad, so both versions have access to the same information.