Setting action for back button in navigation controller

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)?

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];
}

I've implemented UIViewController-BackButtonHandler extension. It does not need to subclass anything, just put it into your project and override navigationShouldPopOnBackButton method in UIViewController class:

-(BOOL) navigationShouldPopOnBackButton {
    if(needsShowConfirmation) {
        // Show confirmation alert
        // ...
        return NO; // Ignore 'Back' button this time
    }
    return YES; // Process 'Back' button click and Pop view controler
}

Download sample app.

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