Swift KVO ( Key Value Observing, Reactive Programming)

 

 

 

//
//  ViewController.swift
//  KVO
//
//  Created by Kyle Lee on 10/12/18.
//  Copyright © 2018 Kyle Lee. All rights reserved.
//

import UIKit


class User: NSObject {
    // send notification (dynamic)
    @objc dynamic var name = String()
    
    @objc var age = 0 {
        willSet { willChangeValue(forKey: #keyPath(age))}
        didSet { didChangeValue(for: \User.age)}
    }
}

class ViewController: UIViewController {

    @IBOutlet weak var nameLabel: UILabel!
    @IBOutlet weak var ageLabel: UILabel!
    @IBOutlet weak var textLabel: UILabel!
    @IBOutlet weak var textField: UITextField!
    
    var nameObservationToken: NSKeyValueObservation?
//    var ageObservationToken: NSKeyValueObservation?
    var inputTextObservationToken: NSKeyValueObservation?
    
    // it is able to absorb notifications
    @objc let user = User()
    // make it observable string
    @objc dynamic var inputText: String?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // observe returns token
        // anything new call the block of code (starts with guard let ..)
        // == \ViewController.user.name
        nameObservationToken = observe(\.user.name, options: [.new]) { (strongSelf, change) in
            guard let updatedName = change.newValue else { return }
            strongSelf.nameLabel.text = updatedName
        }
        
//        ageObservationToken = observe(\.user.age, options: .new) { (strongSelf, change) in
//            guard let updatedAge = change.newValue else { return }
//            strongSelf.ageLabel.text = String(updatedAge)
//        }
        
        inputTextObservationToken = observe(\.inputText, options: .new, changeHandler: { (vc, change)  in
            guard let updatedInputText = change.newValue as? String else { return }
            vc.textLabel.text = updatedInputText
        })
        
        addObserver(self, forKeyPath: #keyPath(user.age), options: .new, context: nil)
        
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        nameObservationToken?.invalidate()
//        ageObservationToken?.invalidate()
        inputTextObservationToken?.invalidate()
    }
    
    @IBAction func didTapUpdateName() {
        user.name = "kilo"
    }
    
    @IBAction func didTapUpdateAge() {
        user.age = 27
    }
    
    @IBAction func textFieldTextDidChange() {
        inputText = textField.text
    }
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        
        if keyPath == #keyPath(user.age) {
            guard let updatedAge = change?[.newKey] as? Int else { return }
            ageLabel.text = String(updatedAge)
        }
        
    }


}

 

 

출처: https://www.youtube.com/watch?v=_AWyXA1sPuc