KVO Not Triggering When Value Changes - objective-c

Question

I'm trying to do some tests with Apple's KVC but for some reason I can't get KVO to trigger when I change a value via KVC.
I have the following code:
#import <Foundation/Foundation.h>
#interface Character : NSObject
{
NSString *characterName;
NSInteger ownedClowCards;
}
#property (nonatomic, retain) NSString *characterName;
#property (nonatomic, assign) NSInteger ownedClowCards;
-(void)hasLostClowCard;
-(void)hasGainedClowCard;
#end
#implementation Character
#synthesize characterName;
#synthesize ownedClowCards;
-(void)hasLostClowCard
{
}
-(void)hasGainedClowCard
{
}
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
NSLog(#"Change");
}
#end
int main()
{
Character *sakura;
Character *shaoran;
//---------------------------------------------------------------------
// Here begins the KVO section.
[sakura addObserver:sakura forKeyPath:#"ownedClowCards" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
//Create and give the properties some values with KVC...
sakura = [[Character alloc] init];
[sakura setValue:#"Sakura Kinomoto" forKey:#"characterName"];
[sakura setValue:[NSNumber numberWithInt:20] forKey:#"ownedClowCards"];
shaoran = [[Character alloc] init];
[shaoran setValue:#"Li Shaoran" forKey:#"characterName"];
[shaoran setValue:[NSNumber numberWithInt:21] forKey:#"ownedClowCards"];
//Done! Now we are going to fetch the values using KVC.
NSString *mainCharacter = [sakura valueForKey:#"characterName"];
NSNumber *mainCharCards = [sakura valueForKey:#"ownedClowCards"];
NSString *rival = [shaoran valueForKey:#"characterName"];
NSNumber *rivalCards = [shaoran valueForKey:#"ownedClowCards"];
NSLog(#"%# has %d Clow Cards", mainCharacter, [mainCharCards intValue]);
NSLog(#"%# has %d Clow Cards", rival, [rivalCards intValue]);
[sakura setValue:[NSNumber numberWithInt:22] forKey:#"ownedClowCards"];
}
Like you can see it's really, really basic code, so I'm ashamed I can't get this to work for whatever reason. Everything I'm trying to do is to get a notification when ownedClowCards changes. I am registering the observers. When I run my program, I expect to see the message "Changed" once when the program is done running. But it never does. Changed is never printed to my program so I assume observeValueForKeyPath:ofObject:change:context: is not getting called.
Any help?

Answer 1

[sakura addObserver:sakura forKeyPath:#"ownedClowCards" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
You are doing the above before initializing sakura. Of course setting nil to observe changes to nil does nothing.

Answer 2

You add your observer to an object that doesn't exist yet.
Character *sakura;
This simply declares the variable, but doesn't actually allocate or initialize it yet.
Try calling sakura = [[Character alloc] init]; before you register as an observer.
And by the way NSString properties usually use the copy flag and not retain. And a memory management flag (assign) doesn't make sense in the case of a primitive type (NSInteger).