NSMutableArray to NSUserDefults not saving - objective-c

Question

I am reading and writing an array to NSuserdefults in this way:
indexDelete = button.tag;
NSUserDefaults *currentDefaults = [NSUserDefaults standardUserDefaults];
NSData *dataRepresentingSavedArray = [currentDefaults objectForKey:#"save"];
if (dataRepresentingSavedArray != nil)
{
NSArray *oldSavedArray = [NSKeyedUnarchiver unarchiveObjectWithData:dataRepresentingSavedArray];
if (oldSavedArray != nil)
myIntegers = [[NSMutableArray alloc] initWithArray:oldSavedArray];
else
myIntegers = [[NSMutableArray alloc] init];
}
[myIntegers addObject:[NSNumber numberWithInteger:indexDelete]];
NSLog (#"Array myIntegers: %#", myIntegers);
[[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:myIntegers] forKey:#"save"];
Every thing works fine if I keep the line:
myIntegers = [[NSMutableArray alloc] init];
out of the brackets, because even if the data is there, it is not written or read correctly:
I get this error: -[NSKeyedUnarchiver initForReadingWithData:]: data is NULL
What im I doing wrong??

Answer 1

Change this:
[[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:myIntegers] forKey:#"save"];
to
[[NSUserDefaults standardUserDefaults] setObject:myIntegers forKey:#"save"];
if myIntegers will not be mutated (changed) in the future. If it will be changed then use:
[[NSUserDefaults standardUserDefaults] setObject:[NSArray arrayWithArray:myIntegers] forKey:#"save"];
The ability to save arrays and dictionaries in the user defaults is documented in the class description.

Answer 2

You never initialize your myIntegers. The first time you get the object for key save from your defaults you get a nil object (hence not entering the if closure and allocating the structure). After that you try to archive a nil object, which is probably the cause for the error you're getting.
Try moving the initialization of the array before this and only adding the objects from the previous saving if they exist:
myIntegers = [[NSMutableArray alloc] init];
NSUserDefaults *currentDefaults = [NSUserDefaults standardUserDefaults];
NSData *dataRepresentingSavedArray = [currentDefaults objectForKey:#"save"];
if (dataRepresentingSavedArray != nil)
{
NSArray *oldSavedArray = [NSKeyedUnarchiver unarchiveObjectWithData:dataRepresentingSavedArray];
if (oldSavedArray != nil)
[myIntegers addObjectsFromArray:oldSavedArray];
}

Answer 3

I have one alternative to do this is to save mutablearray in doc dir and then retrieve it:
// Get path to documents directory
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
NSUserDomainMask, YES);
if ([paths count] > 0)
{
// Path to save array data
NSString *arrayPath = [[paths objectAtIndex:0]
stringByAppendingPathComponent:#"array.out"];
// Write array
[yourMutableArray writeToFile:arrayPath atomically:YES];
// Read both back in new collections
NSMutableArray *arrayFromFile = [NSMutableArray arrayWithContentsOfFile:arrayPath];
for (NSString *element in arrayFromFile)
NSLog(#"Items: %#", element);
}