I am also not sure that I fully understand this scenario, but it doesn't appear that you would need KVO. Do the "tasks" or the "Brain" have any properties to observe? As Ben points out, KVO really shines when you need to keep a UI in sync with the state of a model. If "tasks" just need to know when the "Brain" is done thinking, I would just use standard notifications. NSString * const BrainFinishedThinkingNotification = @"BrainFinishedThinkingNotification" When the Brain has a thought... send a notification: (inside Brain class) - (void) thinkOfSomething { // create idea // send notification when finished [[NSNotificationCenter defaultCenter] postNotificationName:BrainFinishedThinkingNotification withObject:self]; // (you could include extra data in a userInfo object) } That's it, the Brain doesn't have to know about Tasks. The task class can then register for changes, and respond to the notification: [[NSNotification defaultCenter] addObserver:self selector:@selector(brainFinishedThinking:) name:BrainFinishedThinkingNotification object:nil]; handle them in: - (void) brainFinishedThinking:(NSNotification *)n { // access the Brain if necessary Brain *theBrain = (Brain *)[n object]; // do something } Tasks don't need an explicit reference to Brain. Brian On Sat, Sep 5, 2009 at 2:16 AM, Matt Aimonetti<mattaimonetti@gmail.com> wrote:
Hi list,
Coming from a Ruby background, I try to understand and pick the best from Obj-C/Cococa and learn how to use brilliant ideas to improve my coding.
Tonight I was working on a simple demo app to learn how things are done in the Obj-C world and see how they would transpose to the MacRuby world.
Everything went well until the KVO question came along.
Let's say I have a controller that we are going to call Brain. We also have a lot of simpler objects that don't do anything but having a state and being displayed, we are going to call them Task instances. The brain is called every X seconds to "think".
My understanding is that an Obj-C developer would register all the tasks instance with the brain using a KVO and the brain would send notifications when it's being called to "think". So, every time a new task is being created, an observer is added on the brain with the new task key. Each Task instance has an observeValueForKeyPath:ofObject:change:context: method implemented which checks that the notification is meant for itself and if it is, to act accordingly.
While the concept is simple and attractive. I wonder if it wouldn't be simpler to forget about kvo's and simply keep the list of registered tasks in the brain and the brain would call the tasks directly and tell them to change.
It sounds to me that in the MacRuby world, it would be more efficient. If we have 250 tasks for instance, when a notification is being sent, every single task in the 250 tasks created, will receive the notification and will check what to do with it. If we had a simple hash/dictionary in the brain, we could directly find the task to handle and call it directly without having to go through the 250.
Am I missing something or in this specific case and because we use Ruby, KVO aren't the way to go?
Thanks for your help,
- Matt
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