Keeping track of SKNodes for a category - ios

Question

I have a function that adds enemies to my scene that get called by an timing interval
How can I keep track of the number of enemies on the Scene to limit the amount of enemies I have in each level?
**In my update function **
CFTimeInterval timeSinceLastEnemy = currentTime - self.lastEnemyUpdateTime;
self.lastEnemyUpdateTime = currentTime;
if (timeSinceLastEnemy > 1) { // more than a second since last update
timeSinceLastEnemy = 1.0 / 60.0;
self.lastEnemyUpdateTime = currentTime;
}
[self spwanEnemyWithTime:timeSinceLastEnemy];
**The timer and The method to add enemies **
- (void)spwanEnemyWithTime:(CFTimeInterval)timeSinceLast {
self.lastEnemySpawn += timeSinceLast;
if (self.lastEnemySpawn > 0.6) {
self.lastEnemySpawn = 0;
[self spawnEnemy];
}
}
-(void) spawnEnemy {
SKSpriteNode *enemy = [SKSpriteNode spriteNodeWithImageNamed: enemySprite];
int minX = 5;
int maxX = self.frame.size.width;
int rangeX = maxX - minX;
int actualX = (arc4random() % rangeX) + minX;
// Create the enemy slightly off-screen along the upper edge,
enemy.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(enemy.size.height - 10 , enemy.size.width)];
enemy.physicsBody.dynamic = YES;
enemy.physicsBody.categoryBitMask = enemyCategory;
enemy.physicsBody.contactTestBitMask = bulletCategory;
enemy.physicsBody.collisionBitMask = 0;
// and along a random position along the X axis as calculated above
enemy.position = CGPointMake(actualX, self.frame.size.height + enemy.size.height);
[self addChild:enemy];
enemy.xScale = 0.2;
enemy.yScale = 0.2;
enemy.zPosition = 4;
// Create the actions
SKAction * actionMove = [SKAction moveToY:(0 - enemy.size.height) duration:4];
SKAction * actionMoveDone = [SKAction removeFromParent];
[enemy runAction:[SKAction sequence:#[actionMove, actionMoveDone]]];
}

Answer 1

I confess I couldn't grasp what you are doing with the double timers, so I will assume that portion works as you want it to. for the enemy count couldn't this be as simple as incrementing a counter on your spawnEnemy and decrementing the counter when the enemy removes itself from the scene?
You'll have to double check my Obj-c I haven't used it in a while.
int enemyCount = 0;
-(void) spawnEnemy {
enemyCount += 1
...
// Create the actions
SKAction *actionMove = [SKAction moveToY:(0 - enemy.size.height) duration:4];
SKAction *actionMoveDone = [SKAction removeFromParent];
SKAction *decrementCount = [SKAction runBlock: ^(void) {
enemyCount -= 1;
}];
[enemy runAction:[SKAction sequence:#[actionMove, actionMoveDone, decrementCount]]];
}
FYI you have a typo in your method "spwanEnemyWithTime"