How to Create a Value for key

Question

Im trying to have my SKNode have a value forkey that I can access to get a value from. Its just like the name property (skspritenode.name) but I want to be able to have booleans be the value.

This is how I'm trying to create this value.

block.setValue(false, forUndefinedKey: "is-Block")

Then when I try to access it I use this

if block.valueForKey("is_Block") == true {
   //run code here
}

I'm stumped. Any suggestions? I apologize if this is a little confusing. I'm not good at explaining simple things.

Answer 1

The issue is that is_Block does not exist on SKNode.

setValue forUndefinedKey will raise NSUndefinedKeyException by default.

If you had a subclass, you would override this function to do what you want to do.

See https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/KeyValueCoding/Articles/BasicPrinciples.html to better understand key value coding.

If you want to have SKNode have a custom variable named is_Block, you are going to have to create an extension for SKNode, and create a property that will store this data for you.

import Foundation
import SpriteKit
import ObjectiveC

extension SKNode{
    var isBlock: Bool {
        get {
            var key = "isBlock";

            guard let block = objc_getAssociatedObject(self, &key) as? Bool
            else{
                print("Error");
                return false
            }
            print("Success");
            return block
        }
        set(newValue) {
            var key = "isBlock";
            print("Setting \(newValue)")
            objc_setAssociatedObject(self, &key, newValue , objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
        }
    }

}

Test in playground:

import Foundation
import SpriteKit
import ObjectiveC

extension SKNode{
    var isBlock: Bool {
        get {
            var key = "isBlock";

            guard let block = objc_getAssociatedObject(self, &key) as? Bool
            else{
                print("Error");
                return false
            }
            print("Success");
            return block
        }
        set(newValue) {
            var key = "isBlock";
            print("Setting \(newValue)")
            objc_setAssociatedObject(self, &key, newValue , objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
        }
    }

}


let a = SKNode()
let b = SKNode()

a.isBlock = false
b.isBlock = true
print ("\(a.isBlock), \(b.isBlock)")    

b.isBlock = false
a.isBlock = true
print ("\(b.isBlock), \(a.isBlock)")