Unable to pass value back to parentViewController - ios

Question

I have masterViewController and detailViewController. Masterview pushes detailView. When going back to masteViewController I want to update the foo value. But I only get NULL from nslog. How can I set the parenteViewContrller.foo value to #"bar" when navigationback?
masterViewController.h
NSString *foo;
-(void)setFoo:(NSString *)fooValue
#property(nonatomic, retain) NSString *foo;
masterViewController.m
#synthesize foo;
-(void)setFoo:(NSString *)fooValue{
NSLog(#"updated foo:%#", fooValue);
}
detailViewController.m
-(void)goBack{
[self.navigationController.parentViewController setValue:#"bar" forKey:#"foo"];
[self.navigationController popViewControllerAnimated:YES];
}

Answer 1

[UIViewController parentViewController] will not return what you are expecting from iOS 5 onward, instead you should be using [UIViewController presentingViewController]
If you are just targeting iOS 5, it is easy enough to start using presentingViewController instead, but if not I would advise that you manually pass your UIViewController on:
// DetailViewController.h
#class MasterViewController;
#interface DetailViewController : UIViewController
#property (assign, nonatomic) MasterViewController *masterViewController;
#end
// DetailViewController.m
#import "DetailViewController.h"
#import "MasterViewController.h"
#implementation DetailViewController
- (void)goBack {
[self.masterViewController setFoo:#"bar"];
// dismiss this view controller
}
#end
// MasterViewController.h
#interface MasterViewController : UIViewController
- (void)setFoo:(NSString *)bar;
#end
// MasterViewController.m
#import "MasterViewController.h"
#import "DetailViewController.h"
#implementation MasterViewController
- (void)goForward {
DetailViewController *detailViewController = ...;
[detailViewController setMasterViewController:self];
// present this view controller
}
#end

Answer 2

In order for setValue:ForKey: to work, your view controller must conform to NSKeyValueCoding protocol.
Try this:
-(void)goBack{
[self.navigationController.parentViewController setFoo:#"bar"];
[self.navigationController popViewControllerAnimated:YES];
}
and don't forget to retain/release appropriately in your setFoo: method. You probably also need to type cast parentViewController to avoid any warnings.

Answer 3

Pass the reference of the master with assign property to detail view.
Using this reference set the foo value before performing pop action.

Answer 4

gIf you want to pass a object to the parent you could try creating an external object in a header file and importing the header in the controller where you want to use it however THIS IS NOT BEST PRACTICE but it's a quick fix
import
extern MyObject* Object;
#interface GlobalVariables : NSObject {
}
#end
All you have to do now is include the header in the controllers and use the global variable.
If you want to do it by the books i suggest you create a delegate that handles the object passing.

Answer 5

Normally, under this scenario, you need to use delegate. Check out my answer to this similar question in this SO.