Unarchiving encoded data returning nil and incorrect format

Question

I have added category methods to NSUserDefaults to store and retrieve encoded objects (in this case, an NSArray). I am having a problem retrieving the encoded data. Here is my code:

- (void)encodeObject:(id<NSCoding>)object forKey:(NSString *)key {
    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:object requiringSecureCoding:NO error:nil];
    [self setObject:data forKey:key];
    [self synchronize];
}

- (id)decodeObjectForKey:(NSString *)key class:(Class)aClass {
    NSData *data = [self objectForKey:key];
    NSError *error = nil;
    id object = [NSKeyedUnarchiver unarchivedObjectOfClass:aClass fromData:data error:&error];
    NSLog(@"E: %@ %@", error.localizedDescription, object);
    return object;
}

Calling [[NSUserDefaults standardDefaults] encodeObject:object forKey:key] should encode the object passed and store it in defaults, and then calling [[NSUserDefaults standardDefaults] decodeObjectForKey:key class:aClass should return the encoded object.

The problem is that [NSKeyedUnarchiver unarchivedObjectOfClass:fromData:error:] is returning nil, and the error text is logged as The data couldn’t be read because it isn’t in the correct format.. The data retrieved using [self objectForKey:] is of type __NSCFData. I don't know if this is relevant since AFAIK __NSCFData is toll-free bridged to NSData.

Replacing [NSKeyedUnarchiver unarchivedObjectOfClass:fromData:error:] with [NSKeyedUnarchiver unarchiveObjectWithData:] solves the problem. The data are stored and retrieved correctly. But this method is now deprecated so I need to move to the more modern method, but cannot identify why it isn't working.

Answer 1

I had a similar issue. I found that I had to pass in the classes for the objects that were in the NSArray.

NSSet *set = [NSSet setWithArray:@[
                      [NSArray class],
                      [STUFF_IN_ARRAY class]
                      ]];

NSArray *results = [NSKeyedUnarchiver unarchivedObjectOfClasses:set fromData: rawData error: &error];