Question

I’m trying to figure out why pushing a viewController in my tableView using didSelectRowAtIndexPath would cause a crash in iOS 4.3, but in iOS 5.0+, it works fine.

It crashes right when I call:

self.customViewController = [[[CustomViewController alloc] initWithNibName:@"CustomViewController"bundle:nil] autorelease];

anytime after the first time the customViewController has been pushed.

Here’s my relevant code:

@property (nonatomic, retain) CustomViewController *customViewController;

-(void) dealloc // Dealloc of tableView.
{

[customViewController release];
customViewController = nil;

}


- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{

self.customViewController = [[[CustomViewController alloc] initWithNibName:@"CustomViewController"bundle:nil] autorelease]; // Release old, allocate new, set it.

[[self navigationController] pushViewController:customViewController animated:YES];
[customViewController release]; // Balance out pushViewController's retain.


}

Thanks.

Answer 1

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
self.customViewController = [[[CustomViewController alloc] initWithNibName:@"CustomViewController"bundle:nil] autorelease];
[[self navigationController] pushViewController:customViewController animated:YES];
[customViewController release]; // Balance out pushViewController's retain. ---->NO
}

The last release is an extra one that is not needed.
You already have done an autorelease on it to have it’s retain count down by one.

---

We will analyse this line

self.customViewController = [[[CustomViewController alloc] initWithNibName:@"CustomViewController"bundle:nil] autorelease];

you create a CustomViewController retain count == 1.
You say autorelease on it so retain count will be 0 later (probably the end of the run loop), but for now it’s still 1 that is why you still have access to it, but treat it as 0.
After that you say self.customViewController, that property is retain, so retain count == 1.
And you are taking care of that 1 in your dealloc.
As of your comment :

// Balance out pushViewController’s retain.

You don’t Balance those, you balance only the one YOU own. If the system make retain on your objects, it will release them when the system don’t need them anymore.