为什么保留人数如此之高？ 内存管理

Question

I have been going back through my app trying to handle all the memory problems and reading up on memory management. I began using [object retainCount] to trace my memory allocation. Is this to be trusted because I keep finding the counts really strange?

Could someone explain the following:

Bear in mind this the app delegate and an empty mainViewController makes no difference. The initWithRootViewController is causing the count to go up, but I don't see another way of adding one....

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


/* Create the View Controllers */  
UIViewController *mainViewControl = [[[MainViewController alloc] init] autorelease];


/* Create the Navigation Controller */
UINavigationController *navigationController = [[[UINavigationController alloc] initWithRootViewController:mainViewControl] autorelease];


NSLog(@"retain count: %i",[mainViewControl retainCount]);

/* Set the toolbar to purple */
navigationController.navigationBar.barStyle = UIBarStyleBlackTranslucent;
navigationController.navigationBar.tintColor = [UIColor colorWithRed:.6 green:.1 blue:.4 alpha:0.4];
navigationController.navigationBar.translucent = YES;

NSLog(@"retain count: %i",[mainViewControl retainCount]);
navigationController.toolbar.barStyle = UIBarStyleBlackTranslucent;
navigationController.toolbar.tintColor = [UIColor colorWithRed:.6 green:.1 blue:.4 alpha:0.4];
navigationController.toolbar.translucent = YES;

[navigationController setNavigationBarHidden:YES animated:NO];
[navigationController setToolbarHidden:YES animated:NO];

NSLog(@"retain count: %i",[mainViewControl retainCount]);

[window addSubview:[navigationController view]];

NSLog(@"retain count: %i",[mainViewControl retainCount]);

And this is the log ~

2011-01-17 19:47:21.278 ANA[5653:207] 3
2011-01-17 19:47:21.282 ANA[5653:207] 4
2011-01-17 19:47:21.286 ANA[5653:207] 7
2011-01-17 19:47:21.287 ANA[5653:207] 12
2011-01-17 19:47:21.301 ANA[5653:207] Load View

I don't understand why changing those properties or referencing the navigationController is causing the retain count to shoot up.

I have done it without the autoreleases and manually released too but the result is the same. Basically I don't get it, and wonder if the retainCount command is reliable, because if I can't understand this, I don't think I can debug any memory issues elsewhere...

Answer 1

As stated in the official documentation for -retainCount ,

Important: This method is typically of no value in debugging memory management issues. Because any number of framework objects may have retained an object in order to hold references to it, while at the same time autorelease pools may be holding any number of deferred releases on an object, it is very unlikely that you can get useful information from this method.

Don't rely on -retainCount . Other objects may be retaining your object without you knowing it, and autoreleased objects might give you a wrong impression of the actual retain count.

You can rely on Apple's framework objects to do the right thing and relinquish ownership of your object when appropriate, and you need to make sure you are doing that as well.