PopViewController strange behaviour

Question

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 UINavigationControlle

Answer 1

(My previous post was completely wrong. This is a complete rewrite with an appropriate solution.)

I had this behavior pop up when I chose to delete some code generating a warning when I was converting to ARC -- code that I thought was not being called.

Here's the situation:

If you shadow navigationBar:shouldPopItem: in a subclass of UINavigationController, then the current view controller will NOT be popped when the user touches the NavBar's BACK button. However, if you call popViewControllerAnimated: directly, your navigationBar:shouldPopItem: will still be called, and the view controller will pop.

Here's why the view controller fails to pop when the user touches the BACK button:

UINavigationController has a hidden method called navigationBar:shouldPopItem:. This method IS called when the user clicks the BACK button, and it is the method that normally calls popViewControllerAnimated: when the user touches the BACK button.

When you shadow navigationBar:shouldPopItem:, the super class' implementation is not called, and hence the ViewController is not popped.

Why you should NOT call popViewControllerAnimated: within your subclass' navigationBar:shouldPopItem::

If you call popViewControllerAnimated: within navigationBar:shouldPopItem:, you will see the behavior that you desire when you click the BACK button on the NavBar: You can determine whether or not you want to pop, and your view controller pops if you want it to.

But, if you call popViewControllerAnimated: directly, you will end up popping two view controllers: One from your direct call to popViewControllerAnimated:, and one from the call you added to within navigationBar:shouldPopItem:.

What I believe to be the safe solution:

Your custom nav controller should be declared like this:

@interface CustomNavigationController : UINavigationController  
{
    // .. any ivars you want
}
@end

Your implementation should contain code that looks something like this:

// Required to prevent a warning for the call [super navigationBar:navigationBar shouldPopItem:item]
@interface UINavigationController () 
@end


@implementation CustomNavigationController

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
{
    BOOL rv = TRUE;

    if ( /* some condition to determine should NOT pop */ )
    {
        // we won't pop
        rv = FALSE;

        // extra code you might want to execute ...
    } else
    {
        // It's not documented that the super implements this method, so we're being safe
        if ([[CustomNavigationController superclass]
                instancesRespondToSelector:@selector(navigationBar:shouldPopItem:)])
        {
            // Allow the super class to do its thing, which includes popping the view controller 
            rv = [super navigationBar:navigationBar shouldPopItem:item];

        }
    }

    return rv;
}