back button callback in navigationController in iO

Question

I have pushed a view onto the navigation controller and when I press the back button it goes to the previous view automatically. I want to do a few things when back button is pressed before popping the view off the stack. Which is the back button callback function?

Answer 1

If you're using a Storyboard and you're coming from a push segue, you could also just override shouldPerformSegueWithIdentifier:sender:.

Answer 2

I end up with this solutions. As we tap back button viewDidDisappear method called. we can check by calling isMovingFromParentViewController selector which return true. we can pass data back (Using Delegate).hope this help someone.

-(void)viewDidDisappear:(BOOL)animated{

    if (self.isMovingToParentViewController) {

    }
    if (self.isMovingFromParentViewController) {
       //moving back
        //pass to viewCollection delegate and update UI
        [self.delegateObject passBackSavedData:self.dataModel];

    }
}

Answer 3

it's probably better to override the backbutton so you can handle the event before the view is popped for things such as user confirmation.

in viewDidLoad create a UIBarButtonItem and set self.navigationItem.leftBarButtonItem to it passing in a sel

- (void) viewDidLoad
{
// change the back button to cancel and add an event handler
UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithTitle:@”back”
style:UIBarButtonItemStyleBordered
target:self
action:@selector(handleBack:)];

self.navigationItem.leftBarButtonItem = backButton;
[backButton release];

}
- (void) handleBack:(id)sender
{
// pop to root view controller
[self.navigationController popToRootViewControllerAnimated:YES];

}

Then you can do things like raise an UIAlertView to confirm the action, then pop the view controller, etc.

Or instead of creating a new backbutton, you can conform to the UINavigationController delegate methods to do actions when the back button is pressed.

Answer 4

If you can't use "viewWillDisappear" or similar method, try to subclass UINavigationController. This is the header class:

#import <Foundation/Foundation.h>
@class MyViewController;

@interface CCNavigationController : UINavigationController

@property (nonatomic, strong) MyViewController *viewController;

@end

Implementation class:

#import "CCNavigationController.h"
#import "MyViewController.h"

@implementation CCNavigationController {

}
- (UIViewController *)popViewControllerAnimated:(BOOL)animated {
    @"This is the moment for you to do whatever you want"
    [self.viewController doCustomMethod];
    return [super popViewControllerAnimated:animated];
}

@end

In the other hand, you need to link this viewController to your custom NavigationController, so, in your viewDidLoad method for your regular viewController do this:

@implementation MyViewController {
    - (void)viewDidLoad
    {
        [super viewDidLoad];
        ((CCNavigationController*)self.navigationController).viewController = self;
    }
}

Answer 5

Here's another way I implemented (didn't test it with an unwind segue but it probably wouldn't differentiate, as others have stated in regards to other solutions on this page) to have the parent view controller perform actions before the child VC it pushed gets popped off the view stack (I used this a couple levels down from the original UINavigationController). This could also be used to perform actions before the childVC gets pushed, too. This has the added advantage of working with the iOS system back button, instead of having to create a custom UIBarButtonItem or UIButton.

1. Have your parent VC adopt the UINavigationControllerDelegate protocol and register for delegate messages:

   MyParentViewController : UIViewController <UINavigationControllerDelegate>
   
   -(void)viewDidLoad {
       self.navigationcontroller.delegate = self;
   }
   

2. Implement this UINavigationControllerDelegate instance method in MyParentViewController:

   - (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC {
       // Test if operation is a pop; can also test for a push (i.e., do something before the ChildVC is pushed
       if (operation == UINavigationControllerOperationPop) {
           // Make sure it's the child class you're looking for
           if ([fromVC isKindOfClass:[ChildViewController class]]) {
               // Can handle logic here or send to another method; can also access all properties of child VC at this time
               return [self didPressBackButtonOnChildViewControllerVC:fromVC];
           }
       }
       // If you don't want to specify a nav controller transition
       return nil;
   }
   

3. If you specify a specific callback function in the above UINavigationControllerDelegate instance method

   -(id <UIViewControllerAnimatedTransitioning>)didPressBackButtonOnAddSearchRegionsVC:(UIViewController *)fromVC {
       ChildViewController *childVC = ChildViewController.new;
       childVC = (ChildViewController *)fromVC;
   
       // childVC.propertiesIWantToAccess go here
   
       // If you don't want to specify a nav controller transition
       return nil;
   

   }