Question

Original question is below.
I fixed my problem. I had the same view controller set for the tableview and the mapview. AND I had all of my mapView init in viewDidLoad. These both together made the following problems for me:

1) When the tab bar controller was presented modally and I received a memory warning the viewDidUnload was called (which I did nothing in before). When the modal tab bar controller was dismissed and viewDidLoad was called, it reset my mapView.
2) When the tab bar controller was presented modally and I received a memory warning before moving to the tab with the view controller and then switched to that tab, my viewDidLoad was called in my mapView’s controller which reset my map, AND it didn’t reset the tables properties so that my tableView would not work.

Much thanks to Anomie for helping me debug this issue, and gain a better understanding of how these pieces are all connected. Things work great now, and my App has a better design.

Original Question:
I have an application that has a mapview and when I present a tab bar view controller modally, every once in a while when I cancel the modal view controller the map resets back to the world view like a reset button was pressed on it. A few details:

• This NEVER happens on the simulator
• I notice memory warnings around the time this happens on my device
• I do not do anything when memory warnings happen in my app, so nothing should have touched the mapview

Also, my tableview in my modal view controller sometimes shows up blank as well (aroudn the time of memory warnings). When it comes up blank, the methods normally called to get the number of rows, sections, and data are not called at all. Upon cancelling the modal view controller and re-opening it, the data is there fine, so the data is not getting erased..

Code I used to create the tab bar controller, picker and table:

ABPeoplePickerNavigationController *picker = [[ABPeoplePickerNavigationController alloc] init];
picker.peoplePickerDelegate = self;
// Display only a person's address(es)
NSArray *displayedItems = [NSArray arrayWithObjects:[NSNumber numberWithInt:kABPersonAddressProperty],
                                                           nil];  
picker.displayedProperties = displayedItems;

UITabBarItem *peoplePickerTabBarItem = [[UITabBarItem alloc] initWithTabBarSystemItem:UITabBarSystemItemContacts tag:0];
picker.tabBarItem = peoplePickerTabBarItem;

UITableViewController *tvc = [[UITableViewController alloc] initWithStyle:UITableViewStylePlain];
tvc.tableView.delegate = self;
tvc.tableView.dataSource = self;
UINavigationController *nvc = [[UINavigationController alloc] initWithRootViewController:tvc];
UIBarButtonItem *uibbiCancel = [[UIBarButtonItem alloc] initWithTitle:@"Cancel" style:UIBarButtonItemStylePlain target:self action:@selector(cancelTable)];
tvc.navigationItem.rightBarButtonItem = uibbiCancel;
tvc.title = @"Recents";
UITabBarItem *nvcTabBarItem = [[UITabBarItem alloc] initWithTabBarSystemItem:UITabBarSystemItemRecents tag:2];
nvc.tabBarItem = nvcTabBarItem;

tbc = [[UITabBarController alloc] init];

NSArray *sections = [[NSArray alloc] initWithObjects:picker, nvc, nil];

[tbc setViewControllers:sections];

[self presentModalViewController:tbc animated:YES];
[nvcTabBarItem release];
[uibbiCancel release];
[tvc release];
[peoplePickerTabBarItem release];
[picker release];
[nvc release];
[sections release];
[tbc release];

Answer 1

For your map view, what is probably happening is this: When a UIViewController is not being actively displayed (e.g. it is in a non-displayed tab of a UITabViewController, not the visible view in a UINavigationController, or is hidden by a modally presented view controller), it may release its view if a memory notification occurs. It will then recreate the view when needed.

For your table view, I’m not sure. Are you assigning the data source and delegate to the table view in the code that creates the containing view controller, rather than doing so in the view controller’s viewDidLoad method?