Question

I have created two view controllers in which there is UIImage animations.Its crashing frequently and showing memory leaks in xcode instrument.

My Controllers Code-

- (void)viewDidLoad {
     NSArray *firstArray;
     firstArray = [NSArray arrayWithObjects:    
                    [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"up0001" ofType:@"png"]],
                    [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"up0002" ofType:@"png"]],
                                      ::
                                      ::
                   [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"up0035" ofType:@"png"]], nil];


     imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 1024, 768)];

     imgView = UIViewContentModeScaleToFill;

     [imgView setAnimationImages:firstArray];

     imgView.animationDuration = 1.75;

     imgView.animationRepeatCount = 0;

     [imgView startAnimating];

     [self.view addSubview: imgView];
}
- (void)dealloc {
    [super dealloc];
    [imgView release]; 
    imgView = nil;
}

And I am changing viewcontrollers as my rootviewcontroller by getting appdelegate object and calling following appdelegate function in my Appdelegate.m(Please suggest any good approach)

- (void)changeRootViewController:(NSString *)controllerName
{

    if(self.viewController){
        [self.viewController.view removeFromSuperview];
        self.viewController=nil;
    }

    if (controllerName == @"ViewController") {
        ViewController *lviewController =[[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
        self.viewController =  (RootViewController *)lviewController;
        [lviewController release];
        lviewController.view = nil;
        [self.window setRootViewController:self.viewController]; //LEAKS 100%
    } else if (controllerName == @"MainViewController") {
        // Use a different VC as roowViewController
        MainViewController *lviewController =[[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
        self.viewController =  (RootViewController *)lviewController;
        [lviewController release];
        lviewController.view = nil;
        [self.window setRootViewController:self.viewController]; //LEAKS 100%
    } else if (controllerName == @"SecondViewController") {
        // Use a different VC as roowViewController
        SecondViewController *lviewController =[[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
        self.viewController =  (RootViewController *)lviewController;
        [lviewController release];
        lviewController.view = nil;
        [self.window setRootViewController:self.viewController];  //LEAKS 100%
    }

    [self.window makeKeyAndVisible];
}

And calling this in my respective controlers button pressed as –

AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
[appDelegate changeRootViewController:@"ViewController"];

OR

 AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
[appDelegate changeRootViewController:@"MainViewController"];

I want to manage view controllers from my main controller swapping controllers in and out without Navigationbar.Please help me figure out the best possible approach and avoid leaks as well.

Answer 1

Look at this piece of code:

if (controllerName == @"ViewController") {
        ViewController *lviewController =[[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
        self.viewController =  (RootViewController *)lviewController;
        [lviewController release];
        lviewController.view = nil;
        [self.window setRootViewController:self.viewController]; //LEAKS 100%
    }

When you alloc “lviewController”, its retain count is 1;
when you do “self.viewController” as I suppose viewController is a retained property, then lviewController retain count is increased to 2;
then you release it, balancing the previous alloc, and retain count returns to 1;
finally you assign it to rootViewController, which is a retained property, so again lviewController retain count is 2;
finally when you “swap” view controller in your window, the lviewController is released, so it retain count becomes 1. As you can see, it will never be dealloc’d. This means that each time you call this function, you make a leak.