Collision without physics (Cocos2D + Box2D iOS) - ios

Question

I'm a beginner in the Cocos2D world, and even more in Box2D's. I'm developing an iOS game with these two engines, and what I want, is to have a guy (hero) to pick up coins in a scrolling map.
Well, the problem is the "Contact Listener". I can't seem to understand what it really does, and how I can use it to make the difference between my coins and other bodies (that are all static bodies) around the map.
I set all the coins .isSensor = true to disable collisions. I'm using MyContactListener from raywenderlich.com tutorial.
So, the main question is: How to know what type of body is in collision with the hero's body through the contact listener?
(i've read many tutorials and questions on here and I can't seem to know where to begin)
Thanks!
Edit:
Si, I finally got it to work with sprite.tag, but I can't destroy the bodies and the textures. Sometimes when using [textureB removeFromParentAndCleanup:YES]; I get EXC_BAD_ACCESS.
And as I understood, I can't destroy the body since I'm actually using it.
But when trying to use body->SetUserData(self); in my Hero class
#interface Hero : CCNode {
CCSprite * texture;
CGPoint position;
b2Body* body;
TypeCase type;
}
I get EXC_BAD_ACCESS in my update method:
for(b2Body *b = world_->GetBodyList(); b; b=b->GetNext()) {
if (b->GetUserData() != NULL) {
if ([b->GetUserData() isKindOfClass:[Hero class]])
{
Hero* hero = (Hero*)b->GetUserData();
CCSprite *heroSprite = hero.texture;
heroSprite.position = ccp(b->GetPosition().x * PTM_RATIO,
b->GetPosition().y * PTM_RATIO);
}
else if ([b->GetUserData() isKindOfClass:[Tile class]])
{
Tile* tile = (Tile*)b->GetUserData();
CCSprite *tileSprite = tile.texture;
tileSprite.position = ccp(b->GetPosition().x * PTM_RATIO,
b->GetPosition().y * PTM_RATIO);
}
}
}
I get EXC_BAD_ACCESS when calling isKindOfClass.
Hero userData
b2BodyDef heroBodyDef;
heroBodyDef.fixedRotation = true;
heroBodyDef.type = b2_dynamicBody;
heroBodyDef.position.Set(position.x/PTM_RATIO, position.y/PTM_RATIO);
body = world_->CreateBody(&heroBodyDef);
body->SetUserData(self);
Tile userData
b2BodyDef blockBodyDef;
blockBodyDef.type = b2_staticBody;
blockBodyDef.position.Set(position.x/PTM_RATIO, position.y/PTM_RATIO);
blockBodyDef.userData = self;
b2Body *body = world ->CreateBody(&blockBodyDef);

Answer 1

Don't use physics objects for coins.. this will affect on fps :)
create CCSprite for coins and detect collisions with coin sprite and body->UserData;
Add your coins in CCArray and write something like this in your update method:
CCSprite *sprite = (CCSprite*)yourObject.body->GetUserData();
Coins *coinObject;
CCARRAY_FOREACH(coinsArray, coinObject)
{
if (CGRectIntersectsRect([sprite boundingBox], [coinObject boundingBox]))
{
// collision detected;
}
}
if you want to use physics body for your coins, you need to create typedef for yourObject states, and in your contact listener void ContactListener::EndContact(b2Contact* contact) method change yourObject currentState. currentState is yourObject's property.
Do something like this in void ContactListener::EndContact(b2Contact* contact)
yourObject.currentState = isCollideOnCoin;
and after this in your update add this line:
if (yourObject.currentState == isCollideOnCoin)
{
// collision detected;
}

Answer 2

You can create a custom class (say BodyType) which indicates bodies type (in your case player/coin)
then you can use the user data property on your created bodies :
playerBody->SetUserData(new BodyType(1));
coinBody->SetUserData(new BodyType(2));
In the contact listener there is a method named beginContact which has an argument of type b2Contact* named contact.
Use this argument to get the two bodies :
b2Body* bodyA = contact->GetFixtureA()->GetBody();
b2Body* bodyB = contact->GetFixtureB()->GetBody();
then you can know if your player hit a coin by checking :
if ((bodyA->GetUserData().getType() == 1 && bodyB->GetUserData().getType() == 2) ||
(bodyA->GetUserData().getType() == 2 && bodyB->GetUserData().getType() == 1)) {
// Mark collision or save coin body in a member of your contact listener for removing it later
}
Of course make sure the user data is not null as all bodies will be passed to the contact listener and not all might have the user data member set.
EDIT
Regarding the BAD_ACCESS do the following :
if (b->GetUserData() != NULL) {
id myUserData = (id)b->GetUserData();
if ([myUserData isKindOfClass:[Hero class]])
{
Hero *hero = (Hero *)myUserData;
// Do your stuff
}
}