Question

I need to do the following: a sprite is moved to a position, when the sprite goes to this position, I need to execute the reverse action.
For testing in this example I just print “ok” when I reach that position, avoiding so to over-release the action and to risk some exception.

-(id) init
{
    if( (self=[super init]))
    {
        soldier=[CCSprite spriteWithFile: @"soldier.gif"];
        soldier.position= CGPointMake(250, 250);
        [self addChild: soldier];
        CGPoint position=[soldier convertToNodeSpace: CGPointZero];
        CCMoveTo* move=[CCMoveBy actionWithDuration: 2 position: position];
        [move retain];
        [soldier addObserver: self forKeyPath: @"position" options: NSKeyValueObservingOptionNew context: (void*)move];
        [soldier runAction: move];
    }
    return self;
}

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    CGPoint position= [self convertToNodeSpace: soldier.position];
    if(CGPointEqualToPoint(position, CGPointZero));
    {
        NSLog(@"ok");
    }
}

The problem is that it prints “ok” a lot of times, it should print it only a time, why?

EDIT

I removed the extra ‘;’ :

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    CGPoint position= [self convertToNodeSpace: soldier.position]; // breakpoint here
    if(CGPointEqualToPoint(position, CGPointZero))
    {
        NSLog(@"ok");
    }
}

Now it never prints “ok”.In the breakpoint I print position and the last value is (47,47), it never reaches (0,0).

Answer 1

I wouldn’t use KVO/KVC with cocos2d for the simple reason that cocos2d is not KVC/KVO compliant. A Cocos2D class’ properties might change without you ever getting a notification.

I don’t know if this is the problem here or not, but there’s a good chance if you continue with KVC/KVO you’ll eventually run into problems.