SpriteKit: find all descendants of SKNode of certain class?

5
votes

This question shows how to find all children of a SKNode that belong to a certain class, but what if we want all descendants (e.g., grandchildren) that belong to a certain class?

Is there a native way to do this in SpriteKit, or is the only option to create a recursive form of the solution from the aforementioned question?

The SKNode documentation highlights a search function that lets you find descendants with a certain name, but is there a way to filter descendants by class and not be name? We don't want to assign names to nodes if avoidable.

We're using Swift 3.

2
iosswiftsprite-kitsknode
Turn the answer in that question into an extension on SKNode and then add a recursive call into it. – davecom
@davecom yup just wondering if there's a more elegant or native way to do it, thanks. – Crashalot

2 Answers

3
votes

Just add this extension to your project

import SpriteKit

extension SKNode {
    func allDescendants<Element: SKNode>(byType type: Element.Type) -> [Element] {
        let currentLevel:[Element] = children.flatMap { $0 as? Element }
        let moreLevels:[Element] = children.reduce([Element]()) { $0 + $1.allDescendants(byType: type) }
        return currentLevel + moreLevels
    }
}

Now you can fetch all the descendants of an SKNode having a specific type (e.g. SKSpriteNode) writing

let descendants = node.allDescendants(byType: SKSpriteNode.self)

Example

class Enemy: SKSpriteNode { }

let root = SKNode()
let a = Enemy()
let b = SKNode()
let c = SKNode()
let d = Enemy()

root.addChild(a)
root.addChild(b)
a.addChild(c)
a.addChild(d)

let enemies: [Enemy] = root.allDescendants(byType: Enemy.self)

print(enemies.count) // 2
2
votes

What we did was pass a block to the SKNode function that finds nodes by name, and used * as the search term to avoid assigning a name to desired nodes.

    var descendants = [CustomClass]()
    nodeToSearch.enumerateChildNodes(withName: ".//*") { node, stop in
        if node is CustomClass {
            descendants.append(node as! CustomClass)
        }
    }