Question

If I use this custom getter:

-(NSMutableArray *)queue
{
    if (_queue == nil)
    {
        if ([[NSFileManager defaultManager] fileExistsAtPath:kOfflineQueueFilePath]) {
            return [NSKeyedUnarchiver unarchiveObjectWithFile:kOfflineQueueFilePath];

            //[NSKeyedUnarchiver unarchiveObjectWithFile:kOfflineQueueFilePath];
        }else{
            return [[NSMutableArray alloc] init];
        }
    }
}

_queue is always (null). I don’t know why it happens.

But if I use the same code in init:

  if ([[NSFileManager defaultManager] fileExistsAtPath:kOfflineQueueFilePath]) {            
        sharedQueue.queue =  [NSKeyedUnarchiver unarchiveObjectWithFile:kOfflineQueueFilePath];
    }else{
        sharedQueue.queue = [[NSMutableArray alloc] init];
    }

It works like magic. Why am I doing it wrong?

Answer 1

When you create a custom getter, you need to set the underlying ivar before returning the value.

Change:

if ([[NSFileManager defaultManager] fileExistsAtPath:kOfflineQueueFilePath]) {
    return [NSKeyedUnarchiver unarchiveObjectWithFile:kOfflineQueueFilePath];

    //[NSKeyedUnarchiver unarchiveObjectWithFile:kOfflineQueueFilePath];
}else{
    return [[NSMutableArray alloc] init];
}

To:

if ([[NSFileManager defaultManager] fileExistsAtPath:kOfflineQueueFilePath]) {
    _queue = [NSKeyedUnarchiver unarchiveObjectWithFile:kOfflineQueueFilePath];

    //[NSKeyedUnarchiver unarchiveObjectWithFile:kOfflineQueueFilePath];
}else{
    _queue =  [[NSMutableArray alloc] init];
}
return _queue;