Objective C Class Method to control all existing instances? - objective-c

Question

Is it possible to use the class methods of some NSObject I've made to controls all existing instances?
I want a delegate class to be able to send messages to the Object's class methods which can then react appropriately with everything out there.

Answer 1

Sure. Just have all the objects register for notifications when they're created. For example:
- (id)init {
self = [super init];
if (!self) return nil;
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(announceYourself:)
name:#"MYCLASS_ANNOUNCE"
object:nil];
return self;
}
+ (void)identifyInstances {
[[NSNotificationCenter defaultCenter] postNotificationName:#"MYCLASS_ANNOUNCE" object:self];
}
- (void)announceYourself:(id)notification {
NSLog(#"Instance %p reporting in!", self);
}
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self]; // VERY IMPORTANT -- IT WILL CRASH WITHOUT THIS
[super dealloc];
}

Answer 2

Not without using some collection of the objects. The simplest way to do it would be to store the objects in an array and send them all a message when you want something to happen. Specifically:
static NSMutableArray *allObjects = nil;
+ (void) initialize {
if (!allObjects) {
allObjects = [NSMutableArray new];
}
}
- (id) init {
if (self = [super init]) {
//Each object gets held in an array
[allObjects addObject:self];
}
return self;
}
+ (void) doSomethingToEveryObject {
[allObjects makeObjectsPerformSelector:#selector(doSomethingToThisObject)];
}
- (void) doSomethingToThisObject {
NSLog(#"Did something to %#",self];
}
- (void) release {
[super release];
//When the retain count reaches 1, then all external references have disappeared,
//and the only remaining reference is in the objects array.
if (self.retainCount == 1) {
[allObjects removeObject:self];
}
}