Question

I’m struggling a bit with figuring out how to properly set up my view controllers to gracefully handle memory warnings.

At the moment, I’m getting an EXC_BAD_ACCESS crash from a view further back in the navigation controller stack whenever the app receives a memory warning.

The bad access occurs with my table view. Here’s how I’m instantiating it:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
    UITableView *table = [[[UITableView alloc] initWithFrame:CGRectMake(self.view.bounds.origin.x, self.view.bounds.origin.y, self.view.bounds.size.width, self.view.bounds.size.height - self.navigationController.navigationBar.bounds.size.height) style:UITableViewStyleGrouped] autorelease];
    table.dataSource = self;
    table.delegate = self;

    self.tableView = table;
    [self.view addSubview:table];
    [table release];

    ...other stuff...
}

And here’s my viewDidUnload:

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
    self.tableView = nil;
}

Upon a memory warning, viewDidUnload is called, as expected, but I get an EXC_BAD_ACCESS crash on the self.tableView = nil line.

Am I setting up my tableView in the wrong place? I’m not using a nib file, so should I be building it elsewhere? Am I somehow passing it off to the view controller incorrectly? etc etc

Any help would be much appreciated. I still haven’t grokked the sequence of events that occurs upon a memory warning, and Level 1 Memory Warnings seem to be obnoxiously common.

Answer 1

You’re calling release twice on table; once with a deferred release with autorelease when you’re creating it, and again with [table release]; after you’ve added it as a subview of self.view. Remember, if the property for tableView is ‘retain’, then it will be retained on assignment (when assigned with dot syntax) — and, that addSubview will retain table as well when you add it. So, you just need to leave the autorelease in there — since that deferred release (which will be balanced out by the retain that happens when you say self.tableView = table;.