Another Memory Management Issue - ios

Question

My app runs well until I stop it and restart - whereupon the archive file - highScores.archive is present. Then, the app balks at encoding - I get a EXC_BAD_ACCESS at the first line (for a long time, it didn't happen until I got to the date object I was encoding.
My guess is that I need to put in a retain in a couple of places, but I don't know where.
The code:
FlipHighScores.h
...
#interface FlipHighScores : NSObject <NSCoding> {
//NSString *themeChosen;
NSInteger newHighScore;
NSInteger newScoreStartLevel;
NSInteger newScoreFinishLevel;
NSDate *scoreDateCreated;}
#property (copy, nonatomic) NSString *themeChosen;
#property (nonatomic) NSInteger highScore;
#property (nonatomic) NSInteger scoreStartLevel;
#property (nonatomic) NSInteger scoreFinishLevel;
#property (nonatomic, readonly, strong) NSDate *scoreDateCreated;
...
FlipHighScores.m
...
#synthesize themeChosen = _themeChosen;
#synthesize highScore = _highScore;
#synthesize scoreStartLevel = _scoreStartLevel;
#synthesize scoreFinishLevel = _scoreFinishLevel;
#synthesize scoreDateCreated = _scoreDateCreated;
...
-(void)encodeWithCoder:(NSCoder *)aCoder {
[aCoder encodeObject:_themeChosen forKey:#"_themeChosen"];
NSLog(#"Theme Chosen is %#", _themeChosen);
[aCoder encodeInt:_highScore forKey:#"_highScore"];
[aCoder encodeInt:_scoreStartLevel forKey:#"_scoreStartLevel"];
[aCoder encodeInt:_scoreFinishLevel forKey:#"_scoreFinishLevel"];
NSLog(#"Date Created in encodeWithCoder is %#", _scoreDateCreated);
[aCoder encodeObject:_scoreDateCreated forKey:#"_scoreDateCreated"];}
-(id)initWithCoder:(NSCoder *)aDecoder {
if (self) {
_themeChosen = [aDecoder decodeObjectForKey:#"_themeChosen"];
_highScore = [aDecoder decodeIntForKey:#"_highScore"];
_scoreStartLevel = [aDecoder decodeIntForKey:#"_scoreStartLevel"];
_scoreFinishLevel = [aDecoder decodeIntForKey:#"_scoreFinishLevel"];
_scoreDateCreated = [aDecoder decodeObjectForKey:#"_scoreDateCreated"];
}
return self;}
-(NSString *)description {
NSDate *date = _scoreDateCreated;
NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateStyle:NSDateFormatterShortStyle];
NSString *dateString = [dateFormatter stringFromDate:date];
//NSLog(#"dateString from description is %#", dateString);
NSString *descriptionString = [[NSString alloc] initWithFormat:#"%d %# S:%d F:%d D:%#", _highScore, _themeChosen, _scoreStartLevel, _scoreFinishLevel, dateString];
return descriptionString:}
What I find confusing is that if I delete the save file - highScores.archive and run the app, it runs without problem. I stop and kill the app and then start it again - the first time encoding is called it crashes.
At the line where I encode the themeChosen object. I have read a few posts about decoding issues being fixed with a "retain" or changing to . format (why that would help, I don't really understand). But this is encoding. Decoding will probably be the next question...
I am not using ARC on this project. Maybe when I rebuild the whole thing from scratch...
Oh, I forgot to mention that everything was running smoothly as far as I had tested until I added in tracking the Theme variable. Then things went a smidge awry as mentioned here.

Answer 1

I think your problem is in your -initWithCoder. You're taking the result of -decodeObjectForKey: and directly assigning it to the synthesized ivar. Methods that don't have the word "copy" in their names are generally assumed to return autoreleased objects.
If you directly assign an autoreleased object to a variable, that object will be released in the next run loop, will dealloc itself, and now your variable points to junk memory. When you try to access it, you'll get an exec_bad_access.
What you should be doing is taking advantage of the accessor methods that #synthesize creates for you. Instead of
_themeChosen = [aDecoder decodeObjectForKey:#"_themeChosen"];
you should write
[self setThemeChosen:[aDecoder decodeObjectForKey:#"_themeChosen"]];
or, if you positively must use an equal sign, you could use the syntactic sugar of "dot notation":
self.themeChosen = [aDecoder decodeObjectForKey:#"_themeChosen"]
Which will ultimately be translated into close to the same thing.
The key is: the synthesized setter does more than simply assign the object to the ivar. It also retains the object (actually, in this case, it copies the object because you specified copy in your #property declaration). This is only one of the many, many, many reasons you should never access ivars directly and always use accessors -- especially now that they're essentially written for you automagically by #property/#synthesize.
UPDATE:
You're going to find you have trouble with scoreDateCreated seeing as you declared it as being readonly in its #property declaration. Why's it read only? It doesn't appear to be a derived value, so you're clearly going to have to assign something to it.
If you want it read/write in your object, but only want to expose a read only interface, you can redeclare the #property as read/write in an anonymous category at the top of FlipHighScores.m. So it looks read only to anything that includes the header, but is actually read/write inside your object's implementation.