Question

I have a UINavigationController and in one of it’s view controller, I am making the toolbar not hidden in viewDidAppear. Works just fine. But, in viewDidDisappear, I am setting it as hidden but it does not get hidden. What am I doing wrong? Here’s the relevant code:

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];

    [[self navigationController] setToolbarHidden:NO];

    UIBarButtonItem *buttomSubmit = [[UIBarButtonItem alloc] initWithTitle:@"Submit" 
                                                                   style:UIBarButtonItemStyleBordered 
                                                                  target:self 
                                                                  action:@selector(done)];
    UIBarButtonItem *buttonPrint = [[UIBarButtonItem alloc] initWithTitle:@"Print" 
                                                                     style:UIBarButtonItemStyleBordered 
                                                                    target:self 
                                                                    action:@selector(done)];
    UIBarButtonItem *buttonUnits = [[UIBarButtonItem alloc] initWithTitle:@"Units" 
                                                                    style:UIBarButtonItemStyleBordered 
                                                                   target:self 
                                                                   action:@selector(done)];
    UIBarButtonItem *flexSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace 
                                                                               target:nil 
                                                                               action:nil];

    [self setToolbarItems:[NSArray arrayWithObjects:buttonUnits, flexSpace, buttomSubmit, buttonPrint, nil]];

    [buttomSubmit release];
    [buttonPrint release];
    [buttonUnits release];
    [flexSpace release];
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    [[self navigationController] setToolbarHidden:YES];
}

Thanks!

Answer 1

viewDidDisappear is called after the view has gone off screen. If the view has gone off screen because of pressing the back button it will have been popped off the navigation controller stack.

From the UIViewController class reference notes on the navigationController property:

Only returns a navigation controller if the view controller is in its
stack. This property is nil if a navigation controller cannot be
found.

This means that [self navigationController] is returning nil and therefore the setToolbarHidden message is sent to nil and has no effect.

To hide it after the new view loads which is what you seem to want you could do the hiding in the viewDidAppear method of the new view’s controller instead.