Collision Detection in Cocos2d game?

i am trying to detect Collision of two sprites in the following way...but when i try to run the game no collision takes place.... what am i possibly doing wrong??

- (void)update:(ccTime)dt {



    CGRect projectileRect = CGRectMake(projectile.position.x - (projectile.contentSize.width/2), 
                                       projectile.position.y - (projectile.contentSize.height/2), 
                                       projectile.contentSize.width, 
                                       projectile.contentSize.height);

    //CGRectMake(0,220,320,50);
    CGRect targetRects =  CGRectMake(_monkey.position.x - (_monkey.contentSize.width/2), 
                                 _monkey.position.y - (_monkey.contentSize.height/2), 
                                 _monkey.contentSize.width, 
                                 _monkey.contentSize.height);

        if (CGRectIntersectsRect(projectileRect, targetRects)) {
                    NSLog(@"ha ha Collision detected"); 
        }                       

}

projectile sprite is animating from top of screen to the bottom and monkey sprite is animating from left to right at the bottom the projectile goes through the monkey but the log does not get called???

- (void)update:(ccTime)dt {

CGRect projectileRect = [projectile boundingBox];
CGRect targetRects = [_monkey boundingBox];

if (CGRectIntersectsRect(projectileRect, targetRects))
{
    NSLog(@"ha ha Collision detected");
}

CGRect projectileRects = CGRectMake(projectile.position.x - (projectile.contentSize.width/2), 
                                   projectile.position.y - (projectile.contentSize.height/2), 
                                   projectile.contentSize.width, 
                                  projectile.contentSize.height);
CGRect targetRect = CGRectMake(_monkey.position.x - (_monkey.contentSize.width/2), 
                               _monkey.position.y - (_monkey.contentSize.height/2), 
                               _monkey.contentSize.width, 
                              _monkey.contentSize.height);
if (CGRectIntersectsRect(projectileRects, targetRect)) {
    NSLog(@"@@@@@@@@@@@@@@@@@@@@@@@@@@@@");             
}

}

-(void)spriteMoveFinished:(id)sender {

//NSLog(@"spriteMoveFinished");
CCSprite *sprite = (CCSprite *)sender;
[self removeChild:sprite cleanup:YES];

if (sprite.tag == 1) { 
    [_targets removeObject:sprite];



} else if (sprite.tag == 2) { 
    [_projectiles removeObject:sprite];
}

}

-(void)addTarget {

projectile = [CCSprite spriteWithFile:@"egg.png" rect:CGRectMake(0, 0, 10, 10)];
projectile.position = ccp(_bear.position.x,_bear.position.y-20);
projectile.tag=2;
[self addChild:projectile];

CGPoint realDest = ccp(_bear.position.x, _bear.position.y - 380);

int minDuration = 2.0;
int maxDuration = 4.0;
int rangeDuration = maxDuration - minDuration;
int actualDuration = (arc4random() % rangeDuration) + minDuration;

// Move projectile to actual endpoint
[projectile runAction:[CCSequence actions:
                       [CCMoveTo actionWithDuration:actualDuration position:realDest],
                       [CCCallFuncN actionWithTarget:self selector:@selector(spriteMoveFinished:)],
                       nil]];

// Add to projectiles array
projectile.tag = 2;
[_projectiles addObject:projectile];

}

-(void) registerWithTouchDispatcher
{
    [[CCTouchDispatcher sharedDispatcher] addTargetedDelegate:self priority:0 swallowsTouches:YES];
}

-(BOOL) ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event {

CGPoint touchLocation = [self convertTouchToNodeSpace:touch];


if(CGRectContainsPoint(CGRectMake(0,0,320,50),touchLocation)) 
{
    if (![_walkMonkey isDone]) {
        [_monkey runAction:_walkMonkey];
    }


}
else {

}

return YES;

}

-(void) ccTouchEnded:(UITouch *)开发者_如何学Pythontouch withEvent:(UIEvent *)event {

CGPoint touchLocation = [self convertTouchToNodeSpace:touch];

if(CGRectContainsPoint(CGRectMake(0,0,320,50),touchLocation)) 
{

    [_monkey stopAction:_walkMonkey];

}

}

- (void)ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event {       

    CGPoint touchLocation = [self convertTouchToNodeSpace:touch];

    CGPoint oldTouchLocation = [touch previousLocationInView:touch.view];
    oldTouchLocation = [[CCDirector sharedDirector] convertToGL:oldTouchLocation];
    oldTouchLocation = [self convertToNodeSpace:oldTouchLocation];

    CGPoint translation = ccpSub(touchLocation, oldTouchLocation);    

    if (translation.x > 3) {

        _monkey.flipX=YES;
    }
    else if (translation.x < -3){
        _monkey.flipX=NO;

    }

    if(CGRectContainsPoint(CGRectMake(40,0,240,50),touchLocation)) 
    {

        CGPoint newPos = ccpAdd(translation,_monkey.position);
        if(newPos.x >= 320 || newPos.x <= 20)
        {
            NSLog(@"monkey not walking");
        }
        else {
            newPos.y = 100;
            _monkey.position = newPos;
        }

    }

}

You should use the built-in functionality:

CGRect projectileRect = [projectile boundingBox];
CGRect targetRects = [_monkey boundingBox];

if (CGRectIntersectsRect(projectileRect, targetRects))
{
    NSLog(@"ha ha Collision detected");
}

The boundingBox method takes a couple more things into account, for example if the node is positioned relative to its parent.

Also note that prefixing variables with an underscore is considered bad practice in Objective-C. Apple reserves variable names with leading underscores for their internal libraries. If you really need to classify instance variables, one common way is to suffix them with an underscore.