box2d collision detection, code - cocos2d-iphone

Question

im new to programming, i have tried the ray wenderlich tutorial but im still confused.
i have a sprite called rock, and a sprite called player, im trying to detect collision between them. but im extremely confused. in need of some help.
-(void)addRock {
CCSprite *rock = [CCSprite spriteWithFile:#"rock.png"
rect:CGRectMake(0, 0, 27, 40)];
// Determine where to spawn the target along the X axis
CGSize winSize = [[CCDirector sharedDirector] winSize];
int minX = rock.contentSize.width/2;
int maxX = winSize.width - rock.contentSize.width/2;
int rangeX = maxX - minX;
int actualX = (arc4random() % rangeX) + minX;
// Create the target slightly off-screen along the right edge,
// and along a random position along the X axis as calculated above
rock.position = ccp(actualX, 500);
[self addChild:rock];
// Determine speed of the sprite
int actualDuration = 5;//speed of sprite
}
- (id)init {
if ((self=[super init])) {
CGSize winSize = [[CCDirector sharedDirector] winSize];
CCSprite *player = [CCSprite spriteWithFile:#"Player.png"
rect:CGRectMake(0, 0, 27, 40)];
player.position = ccp(winSize.width/2, winSize.height/4+15);
[self addChild:player];
[self schedule:#selector(gameLogicRock:) interval:0.2];
they are the two sprites, they spawn and position correctly, i only need to detect collision

Answer 1

You have to implement a new class for the collision or say contact listener based on some criteria as tag no. i have an example for you.
// ContactListener.h
#import "Box2D.h"
class ContactListener : public b2ContactListener
{
private:
void BeginContact(b2Contact* contact);
void EndContact(b2Contact* contact);
};
// ContactListener.mm
#import "ContactListener.h"
#import "cocos2d.h"
#import "BodyNode.h"
#import "GameScene.h"
void ContactListener::BeginContact(b2Contact* contact)
{
b2Body* bodyA = contact->GetFixtureA()->GetBody();
b2Body* bodyB = contact->GetFixtureB()->GetBody();
if (bodyA->GetUserData() != NULL && bodyB->GetUserData() != NULL)
{
BodyNode* bNodeA = (BodyNode*)bodyA->GetUserData();
BodyNode* bNodeB = (BodyNode*)bodyB->GetUserData();
if ((bNodeA.tag == GameSceneNodeTagBall && bNodeB.tag == GameSceneNodeTagHole) ||
(bNodeA.tag == GameSceneNodeTagHole && bNodeB.tag == GameSceneNodeTagBall))
{
switch (bNodeA.tag) {
case GameSceneNodeTagBall:
if ([bNodeA isKindOfClass:[Ball class]]) {
Ball* ball = (Ball*)bNodeA;
ball.sprite.visible = NO;
[[GameScene sharedGameScene] gameOver];
}
break;
case GameSceneNodeTagHole:
if ([bNodeB isKindOfClass:[Ball class]]) {
Ball* ball = (Ball*)bNodeB;
ball.sprite.visible = NO;
[[GameScene sharedGameScene] gameOver];
}
break;
default:
break;
}
}
}
}
This is an example of ball and hole collision. You can use this as per your requirement.
Hope this will help you.
Thanks!