Cannot figure out why my app crashes when I use NSKeyedArchivers / NSKeyedUnarchivers

Question

I am developing my first iphone 'Diary' app, which uses custom 'Entry' objects that hold an NSString title, NSString text and NSDate creationDate. When I try to archive an NSMutableArray of Entry objects, and later retrieve them the next time the view loads, the app crashes. I have gone through a bunch of sample codes and examples that use NSKeyedArchivers, but still couldn't figure out why that happens. I am guessing there is a problem with the initialization of the array that holds the entries but not sure...

Here is the code, maybe you could find something that I have persistently overseen..."

//--------- Entry.m---------------

- (id) initWithCoder:(NSCoder *)aDecoder{

if ((self = [super init])) {
    self.title = [[aDecoder decodeObjectForKey:@"title"] retain];
    self.text = [[aDecoder decodeObjectForKey:@"text"] retain];
    self.created = [[aDecoder decodeObjectForKey:@"created"] retain];
}
return self;

}

- (void) encodeWithCoder:(NSCoder *)aCoder{

[aCoder encodeObject:self.title forKey:@"title"];
[aCoder encodeObject:self.text forKey:@"text"];
[aCoder encodeObject:self.created forKey:@"created"];

}

//-------------- Diary View Controller.m

- (NSString *)dataFilePath {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, 
     NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
return [documentsDirectory stringByAppendingPathComponent:kFilename];
}

- (void) writeDataToArchive {
NSMutableData *data = [[NSMutableData alloc] init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc]
                             initForWritingWithMutableData:data];

[archiver encodeObject:self.entriesArray forKey:@"entriesArray"];
[archiver finishEncoding];
BOOL result = [data writeToFile:[self dataFilePath]  atomically:YES];
[archiver release];
[data release];    
}

- (void)addItem:sender {
int count = [entriesArray count] +1;    
NSString *newEntryTitle = [NSString stringWithFormat:@"Entry %d", count];    
Entry *anEntry = [[Entry alloc] initWithTitle:newEntryTitle text:@"-" 
         created:[NSDate date]];
[entriesArray addObject:anEntry];
[self.tableView reloadData];

[anEntry release];
[self writeDataToArchive];
}

- (void)viewDidLoad
{
[super viewDidLoad];
NSString *filePath = [self dataFilePath];
if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {     
     NSData *data = [[NSMutableData alloc]
                     initWithContentsOfFile:[self dataFilePath]];

     NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc]
          initForReadingWithData:data];
     NSMutableArray *array = [unarchiver decodeObjectForKey:@"entriesArray"];     
     entriesArray = [array mutableCopy];
     [array release];
     [unarchiver finishDecoding];
     [unarchiver release];
     [data release];
}
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:
    (NSIndexPath *)indexPath
{
    // ... some other stuff
     NSUInteger row = indexPath.row;
     Entry *entry = [entriesArray objectAtIndex:row];

     cell.textLabel.text = entry.title;
     return cell;
}

Thanks a lot.

score 3 · Answer 1 · answered May 09 '11 at 17:02

When you read an array back out with NSKeyedUnarchivers you always get an unmutable copy back. You would need to declare *array as NSArray or just get rid of array all together.

entriesArray = [[unarchiver decodeObjectForKey:@"entriesArray"] mutableCopy];

And @JeremyP points out another issue. Since you didn't alloc or retain *array you should not release it.

score 2 · Accepted Answer · answered May 09 '11 at 10:31

2

You should not release array in viewDidLoad because you do not own it.

Please review the Cocoa memory management Rules because there are a couple of other memory management issues in your code. In particular,

self.title = [[aDecoder decodeObjectForKey:@"title"] retain];
self.text = [[aDecoder decodeObjectForKey:@"text"] retain];
self.created = [[aDecoder decodeObjectForKey:@"created"] retain];

in your initWithCoder: method all leak on the assumption the properties are retain or copy.

answered May 09 '11 at 10:31

JeremyP

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Thanks, I will look into that. And specifically, the app crashes at view did load. I could track it down to there using breakpoints, but did not understand specifically which line is causing it. – dg024 May 09 '11 at 16:39
I initially had the title and text as NSStrings, and had the properties 'copy' with them, so I changed the 'retain's to 'copy's. Thanks. – dg024 May 09 '11 at 18:20

Cannot figure out why my app crashes when I use NSKeyedArchivers / NSKeyedUnarchivers

2 Answers2