PopViewController strange behaviour

Due to a weird request which I tried to turn down but it didn't work, I had to override the navigationBar's back Button.

I have made a custom UINavigationController subclass and hacked the - (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item method.

Here is my code:

@interface CustomUINavigationController ()

@end

@implementation CustomUINavigationController


#pragma mark - UINavigationBar delegate methods

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item {

    if ([[self.viewControllers lastObject] isKindOfClass:[ViewController1 class]]) {
        ViewController1 *vc1 = (ViewController1 *)[self.viewControllers lastObject];
        [vc1 handleBackAction];
        if (vc1.canPopVC == YES) { 
            [self popViewControllerAnimated:YES];
            return YES;
        } else {
            return NO;
        }
    }

    [self popViewControllerAnimated:YES];
    return YES;
}

@end

All works fine, except when I pop a viewController programmatically. The app crashed every time when I wanted to perform a push after said pop. Turning NSZombie on, revealed that when popping a viewController programmatically, its parent viewController is deallocated. At this point, making a custom backButton is not a option since it will lose the native iOS 7 swipe to popViewController feature.

Crash log:

*** -[ContactsDetailViewController performSelector:withObject:withObject:]: message sent to deallocated instance 0x1806b790

Solution

I'm not 100% certain but I don't think you should actually be popping the view controller in that delegate method.

"should" delegate methods don't normally do something. They just assert whether something should or shouldn't be done.

Change your method to this...

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item {

    if ([[self.viewControllers lastObject] isKindOfClass:[ViewController1 class]]) {
        ViewController1 *vc1 = (ViewController1 *)[self.viewControllers lastObject];
        [vc1 handleBackAction];
        if (vc1.canPopVC == YES) { 
            return YES;
        } else {
            return NO;
        }
    }

    return YES;
}

And see if it works.

All I have done is removed the popViewController calls.

EDIT - How to add a custom back button

In a category on UIBarButtonItem...

+ (UIBarButtonItem *)customBackButtonWithTarget:(id)target action:(@SEL)action
{
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    [button setBackgroundImage:[UIImage imageNamed:@"Some image"] forState:UIControlStateNormal];
    [button setTitle:@"Some Title" forState:UIControlStateNormal];
    [button addTarget:target action:action forControlEvents:UIControlEventTouchUpInside];

    UIBarButtonItem *barButton = [[UIBarButtonItem alloc] initWithCustomView:button];

    return barButtonItem;
}

Now whenever you want to set a custom back button just use...

UIBarButtonItem *backButton = [UIBarButtonItem customBackButtonWithTarget:self action:@selector(backButtonPressed)];