loosing fps after nodes leave screen - objective-c

Question

I am currently working on a simple game in Sprite Kit. In the game, you are a square that moves around and can shoot at enemies. You shoot "Projectiles" which are just a custom class that inherits from SKSpriteNode. The game works great at first but slowly as you continue shooting the FPS rate slowly deteriorates to extremely low. As the projectiles leave the screen however the Node count goes back down to what it was originally before the projectile was fired.
The first thing I tried to fix it was somehow release the projectiles from the scene when they hit the edge. Here is the code where I attempt to do so but it has not worked at all.
-(void)didBeginContact:(SKPhysicsContact *)contact {
if (contact.bodyA.categoryBitMask == projectileCategory) {
if (contact.bodyB.categoryBitMask == edgeCategory) {
[contact.bodyA.node removeFromParent];
}
} else if (contact.bodyA.categoryBitMask == edgeCategory) {
if (contact.bodyB.categoryBitMask == projectileCategory) {
[contact.bodyB.node removeFromParent];
}
}
}

Answer 1

To improve performance, you can remove the projectiles when they are out of the screen inside the update function.
override func update(currentTime: CFTimeInterval) {
for node in self.children as [SKNode] {
if node.name == "projectile" {
if !CGRectContainsPoint(self.frame, node.position)
{
println("removed")
node.removeFromParent()
}
}
}
}