collision detection only happen top of the screen - ios

Question

i am going to make a very simple game like a sprite falling from top and i have to catch it with another sprite , if i don't the sprite will go outside the screen and remove ,, that part is ok , i also add collision detection , main problem is this collision only happen upper side of the screen not collision bottom side of the screen ,why is this happening please help ,(i am new :S),, here is full code
in my .h`then .m
{
CCSprite *right;
CCSprite *left;
NSMutableArray *_left;
}
-(void)ringcreate:(ccTime)dt
{
CGSize winsize = [[CCDirector sharedDirector] winSize];
int minX = left.contentSize.width / 2;
int maxX = winsize.width - left.contentSize.width/2;
int rangeX = maxX - minX;
int actualX = (arc4random() % rangeX) + minX;
left = [CCSprite spriteWithFile:#"2.png"];
left.position = ccp(actualX,winsize.height);
[self addChild:left];
id move3 = [CCMoveTo actionWithDuration:5 position:ccp(winsize.width/2,0)];
[left runAction:move3];
}
-(id) init
{
// always call "super" init
// Apple recommends to re-assign "self" with the "super's" return value
if( (self=[super init]) ) {
self.touchEnabled = YES;
right = [CCSprite spriteWithFile:#"1.png"];
right.position = ccp(0,0);
[self addChild:right];
[self schedule:#selector(ringcreate:) interval:2];
[self schedule:#selector(update:)];
}
return self;
}
-(void) ccTouchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch =[touches anyObject];
CGPoint location =[touch locationInView:[touch view]];
location = [[CCDirector sharedDirector] convertToGL:location];
id move = [CCMoveTo actionWithDuration:1 position:ccp(location.x,location.y)];
[right runAction:move];
}
-(void) update:(ccTime)dt
{
if (CGRectIntersectsRect(right.boundingBox, left.boundingBox)) {
CCLOG(#"collison hoyse");
id move1 = [CCScaleTo actionWithDuration:0.4 scale:0.3];
left.visible = NO;
[left runAction:move1];
}
}

Answer 1

i solved the problem , i just have to add array and update them wining that method ,
-(void) update:(ccTime)dt
{
NSMutableArray *crabToUpdate = [[NSMutableArray alloc] init];
for (CCSprite *crab in crabarray) {
NSMutableArray *ring_to_delete = [[NSMutableArray alloc] init];
for (ring1 in ringarray) {
if (CGRectIntersectsRect(crab.boundingBox, ring1.boundingBox)) {
[ring_to_delete addObject:ring1];
}
}
for (CCSprite *ring1 in ring_to_delete) {
[ringarray removeObject:ring1];
[self removeChild:ring1 cleanup:YES];
}
if (ring_to_delete.count >0) {
[crabToUpdate addObject:crab];
}
[ring_to_delete release];
}
}