Can't get enemy to disappear upon collision - sprite-kit

Question

I have been trying all my resources and thanks to my dear friend Sangon, a member here and the IOS Games by tutorial book from Ray Wenderlich and what I am trying to do is to first of all set categories for each node and then if my player's bullet gets collided with the enemy, I want the enemy to disappear. Now I got some suggestions where to start from but this thing is driving me nuts I have tried and tried and the enemy does not disappear. Please help me on this. thanks.
static const uint32_t EnemyCategory = 1;
static const uint32_t bulletCategory = 2;
- (void) fire:(float)targetAngle {
bullet = [SKSpriteNode spriteNodeWithImageNamed:#"cannonbullet"];
bullet.position = _Player.position;
bullet.physicsBody = [SKPhysicsBody
bodyWithCircleOfRadius:bullet.frame.size.width/2];
bullet.physicsBody.categoryBitMask = bulletCategory;
bullet.physicsBody.collisionBitMask = bulletCategory | EnemyCategory;
bullet.physicsBody.contactTestBitMask = bulletCategory | EnemyCategory;
[self addChild:bullet];
int x = _Player.position.x + 1000 * cos(targetAngle);
int y = _Player.position.y + 1000 * sin(targetAngle);
[bullet runAction:[SKAction moveTo:CGPointMake(x, y) duration:2]];
}
- (void) didBeginContact:(SKPhysicsContact *)contact {
SKPhysicsBody *temp;
if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask) {
temp = contact.bodyB;
} else {
temp = contact.bodyA;
}
if (temp.categoryBitMask == EnemyCategory) {
[temp.node removeFromParent];
}
}
- (void) Enemy:(CGSize)size {
Enemy = [SKSpriteNode spriteNodeWithImageNamed:#"enemy1#2x"];
Enemy.position = CGPointMake(self.size.width/2, self.size.height/2);
Enemy.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:Enemy.frame.size];
Enemy.physicsBody.dynamic = NO;
Enemy.physicsBody.categoryBitMask = EnemyCategory;
[self addChild:Enemy];
}

Answer 1

The only problem that I can see is that you didn't set the SKPhysicsContactDelegate delegate properly
You will have to do something like this:
#interface MyScene : SKScene<SKPhysicsContactDelegate>
Once you do that you will also have to set the scene as the contactDelegate. It would look something like this:
self.physicsWorld.contactDelegate = self;
And after this is done your scene will receive the didBeginContact: and didEndContact: messages automatically. Those methods are not something that you call manually.
Here you can find a tutorial that uses collision detection (and removes the objects after collision detection)
From the documentation ’SKPhysicsContactDelegate’
An object that implements the SKPhysicsContactDelegate protocol can respond when two physics bodies are in contact with each other in a physics world. To receive contact messages, you set the contactDelegate property of a SKPhysicsWorld object. The delegate is called when a contact starts or ends.
Hope this helps