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 https://stackoverflow.com/a/19132881/826435)

In your view controller you just conform to a protocol and perform whatever action you need:

extension MyViewController: NavigationControllerBackButtonDelegate {
    func shouldPopOnBackButtonPress() -> Bool {
        performSomeActionOnThePressOfABackButton()
        return false
    }
}

Then create a class, say NavigationController+BackButton, and just copy-paste the code below:

protocol NavigationControllerBackButtonDelegate {
    func shouldPopOnBackButtonPress() -> Bool
}

extension UINavigationController {
    public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
        // Prevents from a synchronization issue of popping too many navigation items
        // and not enough view controllers or viceversa from unusual tapping
        if viewControllers.count < navigationBar.items!.count {
            return true
        }

        // Check if we have a view controller that wants to respond to being popped
        var shouldPop = true
        if let viewController = topViewController as? NavigationControllerBackButtonDelegate {
            shouldPop = viewController.shouldPopOnBackButtonPress()
        }

        if (shouldPop) {
            DispatchQueue.main.async {
                self.popViewController(animated: true)
            }
        } else {
            // Prevent the back button from staying in an disabled state
            for view in navigationBar.subviews {
                if view.alpha < 1.0 {
                    UIView.animate(withDuration: 0.25, animations: {
                        view.alpha = 1.0
                    })
                }
            }

        }

        return false
    }
}

Answer 2

Easiest way

You can use the UINavigationController's delegate methods. The method willShowViewController is called when the back button of your VC is pressed.do whatever you want when back btn pressed

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated;

Answer 3

Found a solution which retains the back button style as well. Add the following method to your view controller.

-(void) overrideBack{

    UIButton *transparentButton = [[UIButton alloc] init];
    [transparentButton setFrame:CGRectMake(0,0, 50, 40)];
    [transparentButton setBackgroundColor:[UIColor clearColor]];
    [transparentButton addTarget:self action:@selector(backAction:) forControlEvents:UIControlEventTouchUpInside];
    [self.navigationController.navigationBar addSubview:transparentButton];


}

Now provide a functionality as needed in the following method:

-(void)backAction:(UIBarButtonItem *)sender {
    //Your functionality
}

All it does is to cover the back button with a transparent button ;)

Answer 4

For a form that requires user input like this, I would recommend invoking it as a "modal" instead of part of your navigation stack. That way they have to take care of business on the form, then you can validate it and dismiss it using a custom button. You can even design a nav bar that looks the same as the rest of your app but gives you more control.

Answer 5

At least in Xcode 5, there is a simple and pretty good (not perfect) solution. In IB, drag a Bar Button Item off the Utilities pane and drop it on the left side of the Navigation Bar where the Back button would be. Set the label to "Back." You will have a functioning button that you can tie to your IBAction and close your viewController. I'm doing some work and then triggering an unwind segue and it works perfectly.

What isn't ideal is that this button does not get the < arrow and does not carry forward the previous VCs title, but I think this can be managed. For my purposes, I set the new Back button to be a "Done" button so it's purpose is clear.

You also end up with two Back buttons in the IB navigator, but it is easy enough to label it for clarity.

Answer 6

This technique allows you to change the text of the "back" button without affecting the title of any of the view controllers or seeing the back button text change during the animation.

Add this to the init method in the calling view controller:

UIBarButtonItem *temporaryBarButtonItem = [[UIBarButtonItem alloc] init];   
temporaryBarButtonItem.title = @"Back";
self.navigationItem.backBarButtonItem = temporaryBarButtonItem;
[temporaryBarButtonItem release];