iPhone NSMutableArray and NSKeyedUnarchiver unarchiveObjectWithFile release oddity

Question

I archive an array (NSMutableArray) of custom objects that implement the . Once i load it froma file to a retaining property @property (nonatomic, retain) NSMutableArray *buddies; the release count of the object is 2 (correct, it's 1of autorelease + 1 of retain of the property) but then noone releases it and the retain count becames 1, so when i release it i get -[__NSArrayM retainCount]: message sent to deallocated instance (i think because the 1 retain count is the autorelease)

Here's the full code:

BuddieListViewController.h

#import <UIKit/UIKit.h>
#import "Buddie.h"

@interface BuddieListViewController : UITableViewController {
    IBOutlet NSMutableArray *buddies;
    [...]
}
[...]
@property (nonatomic, retain) NSMutableArray *buddies;
[...]
@end

BuddieListViewController.m

#import "BuddieListViewController.h"
#import "Buddie.h"
#import "PreviewViewController.h"

@implementation BuddieListViewController

@synthesize buddies;
[...]
- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        [self loadFromDisk];
    }
    return self;
}

- (void)loadFromDisk {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsPath = [paths objectAtIndex:0];
    NSString *appFile = [documentsPath stringByAppendingPathComponent:@"BuddieArchive.ark"];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:appFile]) {
        self.buddies = [NSKeyedUnarchiver unarchiveObjectWithFile:appFile];
        NSLog(@"1- buddies retain count %d (should be 2, 1 + 1autorelease)", [buddies retainCount]);
    } else {
        self.buddies = [NSMutableArray arrayWithCapacity:1];
    }
}
[...]
- (IBAction)cancelledBuddie:(NSNotification *)notification
{
    [editingBuddie release];
    NSLog(@"2- buddies retain count %d (should be 2, 1 + 1autorelease)", [buddies retainCount]);
    [buddies release]; 
    [self loadFromDisk];
    [self.tableView reloadData];
}

Has anyone some idea of why this happens?

I'm sure your editing it right now, but the code is a tad hard to read. — jps

Kris Markel Kris Markel · Accepted Answer · 2010-10-07T20:12:41

I can't say it better than this:

The number returned by retainCount is useless.

Don't rely on it for anything. Use the Leaks tool in Instruments to determine if you're leaking objects.

If you're crashing, it's most likely that you have a zombie. See this video to find out how to use Instruments to find zombies.

iPhone NSMutableArray and NSKeyedUnarchiver unarchiveObjectWithFile release oddity

3 Answers