Sprite Kit, Remove Sprite for collision - ios

Question

Im making a game in sprite kit and I'm fairly new to iOS programming and i have been working on getting it so when 2 images collide that one is deleted or made invisible. I have been very unsuccessful with this and was wondering if anyone knew how to do it?
Below is the ship (which always stays) and one of the objects to be deleted.
-(void)addShip
{
//initalizing spaceship node
ship = [SKSpriteNode spriteNodeWithImageNamed:#"Spaceship"];
[ship setScale:0.5];
ship.zRotation = - M_PI / 2;
//Adding SpriteKit physicsBody for collision detection
ship.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:ship.size];
ship.physicsBody.categoryBitMask = shipCategory;
ship.physicsBody.dynamic = YES;
ship.physicsBody.contactTestBitMask = DonutCategory | PizzaCategory | ChocolateCategory | SoftCategory | AppleCategory | GrapeCategory | OrangeCategory | BananaCategory;
ship.physicsBody.collisionBitMask = 0;
ship.physicsBody.usesPreciseCollisionDetection = YES;
ship.name = #"ship";
ship.position = CGPointMake(260,30);
actionMoveRight = [SKAction moveByX:-30 y:0 duration:.2];
actionMoveLeft = [SKAction moveByX:30 y:0 duration:.2];
[self addChild:ship];
}
- (void)shoot1 //donut
{
// Sprite Kit knows that we are working with images so we don't need to pass the image’s extension
Donut = [SKSpriteNode spriteNodeWithImageNamed:#"1"];
[Donut setScale:0.15];
// Position the Donut outside the top
int r = arc4random() % 300;
Donut.position = CGPointMake(20 + r, self.size.height + Donut.size.height/2);
Donut.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:Donut.size];
Donut.physicsBody.categoryBitMask = DonutCategory;
Donut.physicsBody.dynamic = YES;
Donut.physicsBody.contactTestBitMask = shipCategory;
Donut.physicsBody.collisionBitMask = 0;
Donut.physicsBody.usesPreciseCollisionDetection = YES;
// Add the Dount to the scene
[self addChild:Donut];
// Here is the Magic
// Run a sequence
[Donut runAction:[SKAction sequence:#[
// Move the Dount and Specify the animation time
[SKAction moveByX:0 y:-(self.size.height + Donut.size.height) duration:5],
// When the Dount is outside the bottom
// The Dount will disappear
[SKAction removeFromParent]]]];
}

Answer 1

You have to set the delegate of your physics world:
self.physicsWorld.contactDelegate = self;
Then, you have a delegate that is called when two objects contact :
- (void)didBeginContact:(SKPhysicsContact *)contact {
SKPhysicsBody *firstBody, *secondBody;
if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask)
{
firstBody = contact.bodyA;
secondBody = contact.bodyB;
}
else
{
firstBody = contact.bodyB;
secondBody = contact.bodyA;
}
if ((firstBody.categoryBitMask & projectileCategory) != 0 &&
(secondBody.categoryBitMask & monsterCategory) != 0)
{
//remove the donut and the target
SKSpriteNode *firstNode = (SKSpriteNode *) firstBody.node;
SKSpriteNode *secondNode = (SKSpriteNode *) secondBody.node;
[firstNode removeFromParent];
[secondNode removeFromParent];
}
}
For more information you can jump to the collision part in this tutorial.