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

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];
}