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

For some threading reasons, the solution mentionned by @HansPinckaers wasn't right for me, but I found a very easier way to catch a touch on the back button, and I wanna pin this down here in case this could avoid hours of deceptions for someone else. The trick is really easy : just add a transparent UIButton as a subview to your UINavigationBar, and set your selectors for him as if it was the real button! Here's an example using Monotouch and C#, but the translation to objective-c shouldn't be too hard to find.

public class Test : UIViewController {
    public override void ViewDidLoad() {
        UIButton b = new UIButton(new RectangleF(0, 0, 60, 44)); //width must be adapted to label contained in button
        b.BackgroundColor = UIColor.Clear; //making the background invisible
        b.Title = string.Empty; // and no need to write anything
        b.TouchDown += delegate {
            Console.WriteLine("caught!");
            if (true) // check what you want here
                NavigationController.PopViewControllerAnimated(true); // and then we pop if we want
        };
        NavigationController.NavigationBar.AddSubview(button); // insert the button to the nav bar
    }
}

Fun fact : for testing purposes and to find good dimensions for my fake button, I set its background color to blue... And it shows behind the back button! Anyway, it still catches any touch targetting the original button.

Answer 2

You can try accessing the NavigationBars Right Button item and set its selector property...heres a reference UIBarButtonItem reference, another thing if this doenst work that will def work is, set the right button item of the nav bar to a custom UIBarButtonItem that you create and set its selector...hope this helps

Answer 3

This approach worked for me (but the "Back" button will not have the "<" sign):

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIBarButtonItem* backNavButton = [[UIBarButtonItem alloc] initWithTitle:@"Back"
                                                                      style:UIBarButtonItemStyleBordered
                                                                     target:self
                                                                     action:@selector(backButtonClicked)];
    self.navigationItem.leftBarButtonItem = backNavButton;
}

-(void)backButtonClicked
{
    // Do something...
    AppDelegate* delegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
    [delegate.navController popViewControllerAnimated:YES];
}

Answer 4

Use isMovingFromParentViewController

override func viewWillDisappear(animated: Bool) {
    super.viewWillDisappear(true)

    if self.isMovingFromParentViewController {
        // current viewController is removed from parent
        // do some work
    }
}

Answer 5

Swift

override func viewWillDisappear(animated: Bool) {
    let viewControllers = self.navigationController?.viewControllers!
    if indexOfArray(viewControllers!, searchObject: self) == nil {
        // do something
    }
    super.viewWillDisappear(animated)
}

func indexOfArray(array:[AnyObject], searchObject: AnyObject)-> Int? {
    for (index, value) in enumerate(array) {
        if value as UIViewController == searchObject as UIViewController {
            return index
        }
    }
    return nil
}

Answer 6

The answer from @William is correct however, if the user starts a swipe-to-go-back gesture the viewWillDisappear method is called and even self won't be in the navigation stack (that is, self.navigationController.viewControllers won't contain self), even if the swipe is not completed and the view controller is not actually popped. Thus, the solution would be to:

1. Disable the swipe-to-go-back gesture in viewDidAppear and only allow using the back button, by using:

   if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)])
   {
       self.navigationController.interactivePopGestureRecognizer.enabled = NO;
   }
   

2. Or simply use viewDidDisappear instead, as follows:

   - (void)viewDidDisappear:(BOOL)animated
   {
       [super viewDidDisappear:animated];
       if (![self.navigationController.viewControllers containsObject:self])
       {
           // back button was pressed or the the swipe-to-go-back gesture was
           // completed. We know this is true because self is no longer
           // in the navigation stack.
       }
   }