How can I prevent two types of SpriteKit nodes from colliding with each other?

Question

I'm writing a small game using Apple Sprite Kit.

I'm having trouble with the collisions. Sometimes I dont want two skSpriteNodes with physicsBodys to interact.

as an example I have the HERO , ENEMYS and SHOTS and I want the SHOTS only to interact with the ENEMYS.

But when 2 shots collide together then they change their position.!

the code for the shot is

   shot.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:shot.size];
   shot.physicsBody.dynamic = YES;
   shot.physicsBody.allowsRotation = FALSE;
   shot.physicsBody.categoryBitMask = playerShotCategory;
   shot.physicsBody.contactTestBitMask = enemyCategory;

and the code for the enemy is

   activeGameObject.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:activeGameObject.size];
    activeGameObject.physicsBody.dynamic = YES;
    activeGameObject.physicsBody.categoryBitMask = enemyCategory;
    activeGameObject.physicsBody.contactTestBitMask = playerCategory | playerShotCategory;
    activeGameObject.physicsBody.allowsRotation = FALSE;

Answer 1

If you only want shots to interact with enemies, you'll need to add this code:

shot.physicsBody.collisionBitMask = enemyCategory;
activeGameObject.physicsBody.collisionBitMask = playerShotCategory|playerCategory;

See the documentation for collisionBitMask for more information. You may need to tinker with the collisionBitMask if you have other categories that you want involved in the collisions.