Question

here is my code , i am trying to get from one view to another without any memory leaks.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    


    firstviewcontroller *first = [[firstviewcontroller alloc] init];
    [window addSubview:first.view];
    [self.window makeKeyAndVisible];

    return YES;
}

-(IBAction)gotosecondview:(id)sender
{ 
    secondviewcontroller *second = [[secondviewcontroller alloc] init];
    [self.view addSubview:second.view];
    [second release];
}

-(IBAction)gotofirstview:(id)sender
{
    [self.view  removeFromSuperview];
}

to make the above code work without crashing , all i have to do is remove [second release].
if I remove it I get memory errors (build and analyze) . how can i solve this problem. and i dont want to use [self.navigationController pushViewController:second animated:YES];
all i am trying to do i navigating from one view to another and vice versa WITHOUT using navigation controller. my firstviewcontroller and secondviewcontroller are of type UIViewController.

Thanks in advance.

Answer 1

You need to keep the current view controller alive while its view is showing (so it can process the user input, etc.).

In your code, you can achieve that in several ways:

• Keep an instance of firstviewcontroller and secondviewcontroller as instance variables, and release them on the dealloc method.
• Keep an instance variable with the currently in use UIViewController and release it when you switch to another view.

The code for the second option would look something like this:

@interface
    UIViewController *currentViewController;
@end

@implementation

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:    (NSDictionary *)launchOptions {

    firstviewcontroller *first = [[[firstviewcontroller alloc] init] autorelease];
    [self switchToViewController:first];

    [self.window makeKeyAndVisible];

    return YES;
}

- (void)switchToViewController:(UIViewController *)aViewController {
    [currentViewController.view removeFromSuperview];
    [currentViewController release];

    currentViewController = [aViewController retain];
    [self.window addSubview:currentViewController.view];
}

-(IBAction)gotosecondview:(id)sender { 
    [self switchToViewController:[[[secondviewcontroller alloc] init] autorelease]];
}

@end

Here, all the logic for maintaining a single UIViewController alive lies in the switchToViewController method, which also handles the logic for switching from one view to another. As an added bonus, you can quickly add support for animations by adding a couple of lines in switchToViewController.