IOS: NSUserDefault for an array of UIImage - ios

Question

I want to store an array of UIImage and I do this:
//in didFinishLaunchingWithOption
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:#"theKey"];
if (data == NULL) arrayImage = [[NSMutableArray alloc] init];
else {arrayImage = [[NSMutableArray alloc] init]; arrayImage = [NSKeyedUnarchiver unarchiveObjectWithData:data];}
NSLog(#"arrayImage:%#", arrayImage);
//and in applicationDidEnterBackground
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:arrayImage];
[defaults setObject:data forKey:#"theKey"];
NSLog(#"arrayImage:%#", arrayImage);
when app run in didFinishLaunchingWithOption in nslog I see all object in my array, but when I use it, I have a crash that say "[__NSArrayM count]: message sent to deallocated instance" why?

Answer 1

I'm not completely sure, but I think that
+(id)unarchiveObjectWithData:(NSData *)data
gives you an autoreleased object, so you may retain it. And I think it will give you a non-mutable object, so when you will try to add or remove objects from it you will get an error (I'm no sure about this, but I think I once was in this situation...)
I would rewrite some part of your code:
...
if (data == nil)
{
arrayImage = [[NSMutableArray alloc] init];
} else
{
//arrayImage = [[NSMutableArray alloc] init]; //why to allocate and initialize if you are goind to unarchive it?
//arrayImage = [[NSKeyedUnarchiver unarchiveObjectWithData:data] retain]; //note the retain here
NSArray *arr = [NSKeyedUnarchiver unarchiveObjectWithData:data]; //the unarchive won't mantain mutability (I guess).
arrayImage = [NSMutableArray arrayWithArray:arr]; //create a mutable copy
}
...

Answer 2

I assume you're not using ARC. The problem is in:
if (data == NULL)
arrayImage = [[NSMutableArray alloc] init];
else {
arrayImage = [[NSMutableArray alloc] init];
// HERE
arrayImage = [NSKeyedUnarchiver unarchiveObjectWithData:data];
}
At HERE, you replace the value in arrayImage with a new instance for the keyed unarchiver. The value you init'd just previously is lost (in fact, leaked). The value from the unarchiver is an autoreleased object, so will be released when the pool is drained. This is before the applicationDidEnterBackground call is made.
The correct solution is to retain the value from the unarchiver. Viz:
if (data == nil)
arrayImage = [[NSMutableArray alloc] init];
else
arrayImage = [[NSKeyedUnarchiver unarchiveObjectWithData:data] retain];