Question

I’m developing an iPhone application that show the camera’s view with this code:

-(void) displayAR {
    [rootViewController presentModalViewController:[self cameraController] animated:NO];
    [displayView setFrame:[[[self cameraController] view] bounds]];
}

And hide the camera’s view with this code:

- (void) hideAR {
    [[self locationManager] stopUpdatingHeading];
    [[self locationManager] stopUpdatingLocation];

    [[self accelerometerManager] release];

    [rootViewController dismissModalViewControllerAnimated:YES];
}

When I call hideAR, I get an EXC_BAD_ACCESS with the following debugger screenshot:

alt text http://img408.imageshack.us/img408/4550/capturadepantalla201006u.png

Any advice?

UPDATE:

I’ve changed hideAR code with this and I’m getting the same error:

- (void) hideAR {

    [rootViewController dismissModalViewControllerAnimated:YES];
}

I’ve checked rootViewController and it isn’t nil.

As you can see on debugger’s screenshot, the last method called (the first on the stack) is: [UIWindowController transitionViewDidComplete:fromView:toView].

Maybe, there is something accessing camera´s view after it was dismissed.

SECOND UPDATE

The class containing these methods is:

@implementation AugmentedRealityController

@synthesize locationManager;
@synthesize accelerometerManager;
@synthesize displayView;
@synthesize centerCoordinate;
@synthesize scaleViewsBasedOnDistance;
@synthesize rotateViewsBasedOnPerspective;
@synthesize maximumScaleDistance;
@synthesize minimumScaleFactor;
@synthesize maximumRotationAngle;
@synthesize centerLocation;
@synthesize coordinates = coordinates;
@synthesize debugMode;
@synthesize currentOrientation;
@synthesize degreeRange;
@synthesize rootViewController;

@synthesize cameraController;

- (id)initWithViewController:(UIViewController *)vc {

    coordinates     = [[NSMutableArray alloc] init];
    coordinateViews = [[NSMutableArray alloc] init];
    latestHeading   = -1.0f;
    debugView       = nil;

    [self setRootViewController: vc];

    [self setDebugMode:NO];
    [self setMaximumScaleDistance: 0.0];
    [self setMinimumScaleFactor: 1.0];
    [self setScaleViewsBasedOnDistance: NO];
    [self setRotateViewsBasedOnPerspective: NO];
    [self setMaximumRotationAngle: M_PI / 6.0];

    CGRect screenRect = [[UIScreen mainScreen] bounds];

    [self setDisplayView: [[UIView alloc] initWithFrame: screenRect]];

    [self setCurrentOrientation:UIDeviceOrientationPortrait];
    [self setDegreeRange:[[self displayView] bounds].size.width / 12];

    [vc setView:displayView];

    [self setCameraController: [[[UIImagePickerController alloc] init] autorelease]];
    [[self cameraController] setSourceType: UIImagePickerControllerSourceTypeCamera];
    [[self cameraController] setCameraViewTransform: CGAffineTransformScale([[self cameraController] cameraViewTransform], 1.13f,  1.13f)];
    [[self cameraController] setShowsCameraControls:NO];
    [[self cameraController] setNavigationBarHidden:YES];
    [[self cameraController] setCameraOverlayView:displayView];

    CLLocation *newCenter = [[CLLocation alloc] initWithLatitude:37.41711 longitude:-122.02528];

    [self setCenterLocation: newCenter];
    [newCenter release];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(deviceOrientationDidChange:)
                                                 name: UIDeviceOrientationDidChangeNotification
                                               object:nil];
    [[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];   

    // Inicializa el gestor del GPS y el del acelerómetro.
    [self startListening];

    return self;
}

THIRD UPDATE

I’ve put some NSLog trace, and I see that displayAR is called after hideAR call. I also see that viewDidAppear method on rootViewController is also called after hideAR. Actually, viewDidAppear is calling displayAR.

Why is called viewDidAppear?

FOURTH UPDATE

I’ve found the line that is failing. This is the first line on displayAR:

[rootViewController presentModalViewController:[self cameraController] animated:NO];

Any ideas? rootViewController and cameraController aren’t nil.

FITH UPDATE

If you want to reproduce my error:

I’m using nielswh’s iPhone-AR-Toolkit (you can download it here).

You can modify the ARKitDemo example include it with the library and try to dismissModalView.

Answer 1

Almost 100% of the time EXC_BAD_ACCESS is from a mistakenly released resource. Without seeing all your code there is no way to know for sure but my best guess is that accelerometerManager is nil

EDIT:

viewDidAppear is being called on the root view controller because it is now being presented again after the other view you had displayed was hidden.

EDIT 2:

From the look of your stack trace, something somewhere at one time registered for an animation callback. It’s entirely possible that whatever that thing is, it’s invalid now after showing/hiding different views and could have been released without you knowing it. Try to sniff out what it is that is listening for an animationDidStop callback, sorry I can’t help more but without having all the code we are left with this shotgun debugging.