objective-c 黒魔術.md

• Associated Object
• Method Swizzling

SwiftでObjective-Cの黒魔術ってどうなった？

import UIKit

var imageDebugStringKey: UInt8 = 0

extension UIImage {
    var debugString: String {
        get {
            return objc_getAssociatedObject(self, &imageDebugStringKey) as? String ?? ""
        }
        set {
            objc_setAssociatedObject(self, &imageDebugStringKey, newValue, .OBJC_ASSOCIATION_RETAIN)
        }
    }
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()


        let img1 = UIImage(named: "img")!
        img1.debugString = "画像１"
        let img2 = UIImage()
        img2.debugString = "画像２"

        print(img1.debugString)
        print(img2.debugString)
    }
}