using flatMap to enumerate SpriteKit nodes - ios

Question

I tried using the following to get all nodes of a certain class:
let enemies = children.flatMap { $0 as? SomeEnemyClass }
The result is an empty array. I would like to understand why I'm not getting any results. enumerateChildNodesWithName works, but it doesn't list the parent/child relationships which I thought might shed some light. Thanks!
Here is the code: There is a simple class for the enemy, a level manager that replaces nodes in the scene editor with enemy objects, and GameScene.swift. Everything gets assigned to a world node.
Enemy Class
class Enemy: SKSpriteNode {
func spawn(parentNode:SKNode, position: CGPoint, size: CGSize = CGSize(width: 50, height: 50)) {
parentNode.addChild(self)
self.size = size
self.position = position
self.name = "enemy"
self.physicsBody = SKPhysicsBody(circleOfRadius: size.width / 2)
self.physicsBody?.affectedByGravity = false
self.physicsBody?.categoryBitMask = PhysicsCategory.enemy.rawValue
self.physicsBody?.contactTestBitMask = PhysicsCategory.hero.rawValue
self.physicsBody?.collisionBitMask = 0
}
}
Level Manager
class LevelManager
{
let levelNames:[String] = ["Level1"]
var levels:[SKNode] = []
init()
{
for levelFileName in levelNames {
let level = SKNode()
if let levelScene = SKScene(fileNamed: levelFileName) {
for node in levelScene.children {
switch node.name! {
case "enemy":
let enemy = Enemy()
enemy.spawn(level, position: node.position)
default: print("Name error: \(node.name)")
}
}
levels.append(level)
}
}
func addLevelsToWorld(world: SKNode)
{
for index in 0...levels.count - 1 {
levels[index].position = CGPoint(x: -2000, y: index * 1000)
world.addChild(levels[index])
}
}
}
GameScene.swift - didMoveToView
world = SKNode()
world.name = "world"
addChild(world)
levelManager.addLevelsToWorld(self.world)
levelManager.levels[0].position = CGPoint(x:0, y: 0)

Answer 1

map and flatMap transform one array into another, what you are really trying to do is just filtering your child nodes for enemies. Use filter instead.
let enemines = children.filter { $0 is SomeEnemyClass }
That said, I don't see any reason why your sample code would not work.
Here is an example of this code working.
This code will only work if you have real classes derived from SKNode. It is much more common to use node name strings to identify types of nodes. This would work if you had a constant string name for your enemies.
let enemies = children.filter { $0.name == "SomeEnemy" }

Answer 2

You said
let enemies = children.flatMap { $0 as? SomeEnemyClass }
The result is an empty array. I would like to understand why I'm not getting any results. enumerateChildNodesWithName works
First of all this code
let enemies = children.flatMap { $0 as? Enemy }
is correct and it does returns an array of Enemy. Specifically all objects inside children that are Enemy or subclasses of Enemy.
Look
Why is not working for you?
You said that enumerateChildNodesWithName si working for you. This makes me think that you don't have Enemy objects into children. You just have SKNode(s) you assigned the name enemy.

Answer 3

What I learned was that the node tree is really a tree and you have to start looking on the right branch to get results. The answer to my question is:
let enemies = childNodeWithName("//level")!.children.flatMap { ($0 as? SomeEnemyClass) }
or
let enemies = childNodeWithName("//level")!.children.filter { $0 is SomeEnemyClass }
This is not an answer to my question, but it works too...
self.enumerateChildNodesWithName("//*") {
node, stop in
if (node.name == "enemy") {
print(node)
}
}
Thank you to everyone who offered their input. It got me pointed in the right direction.