Setting action for back button in navigation contr

Question

I'm trying to overwrite the default action of the back button in a navigation controller. I've provided a target an action on the custom button. The odd thing is when assigning it though the backbutton attribute it doesn't pay attention to them and it just pops the current view and goes back to the root:

UIBarButtonItem *backButton = [[UIBarButtonItem alloc] 
                                  initWithTitle: @"Servers" 
                                  style:UIBarButtonItemStylePlain 
                                  target:self 
                                  action:@selector(home)];
self.navigationItem.backBarButtonItem = backButton;

As soon as I set it through the leftBarButtonItem on the navigationItem it calls my action, however then the button looks like a plain round one instead of the arrowed back one:

self.navigationItem.leftBarButtonItem = backButton;

How can I get it to call my custom action before going back to the root view? Is there a way to overwrite the default back action, or is there a method that is always called when leaving a view (viewDidUnload doesn't do that)?

Answer 1

Swift version of @onegray's answer

protocol RequestsNavigationPopVerification {
    var confirmationTitle: String { get }
    var confirmationMessage: String { get }
}

extension RequestsNavigationPopVerification where Self: UIViewController {
    var confirmationTitle: String {
        return "Go back?"
    }

    var confirmationMessage: String {
        return "Are you sure?"
    }
}

final class NavigationController: UINavigationController {

    func navigationBar(navigationBar: UINavigationBar, shouldPopItem item: UINavigationItem) -> Bool {

        guard let requestsPopConfirm = topViewController as? RequestsNavigationPopVerification else {
            popViewControllerAnimated(true)
            return true
        }

        let alertController = UIAlertController(title: requestsPopConfirm.confirmationTitle, message: requestsPopConfirm.confirmationMessage, preferredStyle: .Alert)

        alertController.addAction(UIAlertAction(title: "Cancel", style: .Cancel) { _ in
            dispatch_async(dispatch_get_main_queue(), {
                let dimmed = navigationBar.subviews.flatMap { $0.alpha < 1 ? $0 : nil }
                UIView.animateWithDuration(0.25) {
                    dimmed.forEach { $0.alpha = 1 }
                }
            })
            return
        })

        alertController.addAction(UIAlertAction(title: "Go back", style: .Default) { _ in
            dispatch_async(dispatch_get_main_queue(), {
                self.popViewControllerAnimated(true)
            })
        })

        presentViewController(alertController, animated: true, completion: nil)

        return false
    }
}

Now in any controller, just conform to RequestsNavigationPopVerification and this behaviour is adopted by default.

Answer 2

By using the target and action variables that you are currently leaving 'nil', you should be able to wire your save-dialogs in so that they are called when the button is "selected". Watch out, this may get triggered at strange moments.

I agree mostly with Amagrammer, but I don't think it would be that hard to make the button with the arrow custom. I would just rename the back button, take a screen shot, photoshop the button size needed, and have that be the image on the top of your button.

Answer 3

Swift 4 iOS 11.3 Version:

This builds on the answer from kgaidis from https://stackoverflow.com/a/34343418/4316579

I am not sure when the extension stopped working, but at the time of this writing (Swift 4), it appears that the extension will no longer be executed unless you declare UINavigationBarDelegate conformity as described below.

Hope this helps people that are wondering why their extension no longer works.

extension UINavigationController: UINavigationBarDelegate {
    public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {

    }
}

Answer 4

Try putting this into the view controller where you want to detect the press:

-(void) viewWillDisappear:(BOOL)animated {
    if ([self.navigationController.viewControllers indexOfObject:self]==NSNotFound) {
       // back button was pressed.  We know this is true because self is no longer
       // in the navigation stack.  
    }
    [super viewWillDisappear:animated];
}

Answer 5

Unlike Amagrammer said, it's possible. You have to subclass your navigationController. I explained everything here (including example code).

Answer 6

There's an easier way by just subclassing the delegate method of the UINavigationBar and override the ShouldPopItemmethod.