Unable to access self.parentViewController.property - ios

Question

I have implemented a subclass of ECSlidingViewController.
InitialViewController.h
#interface InitialViewController : ECSlidingViewController
#property (nonatomic, strong) WebViewController *webVC;
#property (nonatomic, strong) MenuViewController *menuVC;
#end
I need access to the .webVC from the .menuVC, but am unable to access them from self.parentViewController.webVC getting the error:
"UIViewController does not have a member named webVC"
but when I check in the debugger
po self: <MenuViewController>
po self.parentViewController: <InitialViewController>
po self.parentViewController.webVC: error: property 'webVC' not found on object of type 'UIViewController *'
However, when I navigate the object tree of self in the local variable window, I can go
-self <MenuViewController> 0x0000001
-UITableViewController
-UIViewController
-_parentViewController <InitialViewController>
-webVC <WebViewController
-menuVC <MenuViewController> 0x0000001
Where self and self.parentViewController.menuVC have the same memory address
When I navigate down and right-click->print Description, I get
Printing description of self->_parentViewController->menuVC:
<MenuViewController: 0x8e8c720>
Those '->' and the '_' make me think I'm seriously missing something involving pointers and ivars.
I'm also interested if there is a better way to implement this functionality. This kind of smells like I'm breaking MVC with a child Controller knowing about itself and its parent. However, selections on the menu directly manipulate the webView I have loaded.

Answer 1

Answer:
UIViewController does not have this property built in so you need to cast it:
[(InitialViewController*)self.parentViewController webVC]
Explanation:
This is a question of Classes and SubClasses. Say I have a class MyView which is a subclass of UIView. This class has a couple methods on it, -(void)method1; and -(void)method2;. The .h would look something like this:
#interface MyView : UIView
- (void)method1;
- (void)method2;
#end
I then create a MyView* named thisView and assign it to my ViewController's view property:
#import "MyView.h"
- (void)viewDidLoad
{
MyView* thisView = [[MyView alloc] init];
[self setView: thisView];
}
The UIViewController class's property, view is declared like this:
#property (...) UIView* view;
Pay extra special attention to the UIView* there.
Because view is declared as a UIView*, it will accept values that are subclasses of UIView*, but when I access it later, it will give me a MyView in a box labeled UIView.
In other words, consider this code:
- (void)viewDidLoad
{
MyView* thisView = [[MyView alloc] init];
[self setView: thisView];
UIView* returnedView = thisView; //This is perfectly fine
}
UIViewController will return something along the lines of returnedView, which is a MyView in a UIView container.
When your program goes to access the view, all it knows is that has received something in a box labeled "UIView", so it only knows that it can run methods on it that are present in the UIView class. We have to explicitly tell it "No, this is a MyView," and we do that with casting:
[self.view method1]; //This will break
[(MyView*)self.view method1]; //This will work
Back to your problem
When you access self.parentViewController, you are given a InitialViewController in a UIViewController box, so you have to explicitly tell your program that it is an InitialViewController. You do that by casting:
InitialViewController* parentVC = (InitialViewController*)self.parentViewController;
[parentVC.webVC doSomething];
Warning:
Your VC that is accessing webVC must have a declaration of (InitialViewController*), so you'll need to watch out for forward declaration errors.
If you are unfamiliar with this, it is when Class A imports Class B, but Class B also imports Class A:
A
--->Import B
B
--->Import A
Which results in
A
--->Import B
------->Import A
----------->Import B
and so on.
A class cannot import itself.