iOS - KVO programming

declare object:
interface StockData : NSObject {
   NSString * stockName;
   float price;
}
@end
@implementation StockData
@end

Add Observer:
[stockForKVO addObserver:self forKeyPath:@"price" options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:NULL];  

Set Value:
myLabel.text = [stockForKVO valueForKey:@"price"];  

Reset Value, trigger observer method:
[stockForKVO setValue:@"20.0" forKey:@"price"];  


Call observer method:
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if([keyPath isEqualToString:@"price"])
    {
        myLabel.text = [stockForKVO valueForKey:@"price"];
    }

}

Remove observer:
- (void)dealloc
{
    [super dealloc];
    [stockForKVO removeObserver:self forKeyPath:@"price"];
    [stockForKVO release];
}