只能被class继承的协议

• 被@objc修饰的协议,还可以暴露给OC去遵守实现

        protocol Runnable : AnyObject {}
        protocol Runnable : class {}
        @objc protocol Runnable: {}

可选协议

• 可以通过@objc定义可选协议,这种协议只能被class遵守

@objc protocol Runnable {
    func run1()
    @objc optional func run2()//可选协议
    func run3()
}

class HomeViewController: UIViewController, Runnable {
    func run1() {
        
    }
    
    func run3() {
        
    }
}

dynamic

• 被@objc dynamic修饰的内容会具有动态性,比如调用方法会走runtime那一套流程

class Dog: NSObject {
    @objc dynamic func test1(){}//runTime流程
    func test2() { }//虚表
}

KVC \ KVO

• Swift支持KVC\KVO的条件
• 属性所在的类,监听器最终继承自NSObject
• 用@objc dynamic修饰对应的属性

class Observer: NSObject {
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        
        print("observeValue",change?[.oldKey] ?? (Any).self)
        print("observeValue",change?[.newKey] ?? (Any).self)
    }
}

class Person: NSObject {
    @objc dynamic var age: String = "0"
    var observer: Observer = Observer()
    override init() {
        super.init()
        self.addObserver(observer, forKeyPath: "age", options: [.new,.old], context: nil)
    }
    deinit {
        self.removeObserver(observer, forKeyPath: "age")
    }
}

class HomeViewController: UIViewController {

    
    override func viewDidLoad() {
        
        let p = Person()
        p.age = "20"
        p.age = "30"
        p.setValue("25", forKey: "age")
   
    } 
}
//打印结果
observeValue 0
observeValue 20
observeValue 20
observeValue 30
observeValue 30
observeValue 25

block方式的KVO

class Person: NSObject {
    @objc dynamic var age: Int = 0
    var observation: NSKeyValueObservation?
    override init() {
        super.init()
        observation = observe(\Person.age, options: .new, changeHandler: { (_, change) in
            print(change.newValue as Any)
        })
    }
    
}

class HomeViewController: UIViewController {

    override func viewDidLoad() {
        
        let p = Person()
        p.age = 10
   
    } 
}

关联对象(Associated Object)

• 在Swift中,class依然可以使用关联对象
• 默认情况extension不可以增加存储属性
• 借助关联对象,可以实现类似extension为class增加存储属性的效果

class Person { }
extension Person {
    private static var AGE_KEY: Void?
    var age: Int {//可读 可写计算属性,不占用内存空间
        get {
            (objc_getAssociatedObject(self, &Self.AGE_KEY) as? Int) ?? 0
        }
        set {
            objc_setAssociatedObject(self, &Self.AGE_KEY, newValue, .OBJC_ASSOCIATION_ASSIGN)
        }
    }
    
}
class HomeViewController: UIViewController {

    override func viewDidLoad() {
        
        let p = Person()
        print(p.age)//0
        p.age = 10;
        print(p.age)//10
   
    } 
}

资源名管理

        let img = UIImage(named: "logo")
        let btn = UIButton(type: .custom)
        btn.setTitle("添加", for: .normal)
        performSegue(withIdentifier: "login_main", sender: self)

• 这种做法实际上参考了Android的资源名管理方式

enum R {
    enum string: String {
        case add = "添加"
    }
    enum image: String {
        case logo
    }
    enum segue: String {
        case login_main
    }
}

class HomeViewController: UIViewController {

    override func viewDidLoad() {
        
        let img = UIImage(named: R.image.logo.rawValue)
        let btn = UIButton(type: .custom)
        btn.setTitle(R.string.add.rawValue, for: .normal)
        performSegue(withIdentifier: R.segue.login_main.rawValue, sender: self)
   
    } 
}

enum R {
    enum string: String {
        case add = "添加"
    }
    enum image: String {
        case logo
    }
    enum segue: String {
        case login_main
    }
}

extension UIImage {
    convenience init?(_ name: R.image) {
        self.init(named: name.rawValue)
    }
}
extension UIViewController {
   func performSegue(withIdentifier identifier: R.segue, sender: Any?){
        performSegue(withIdentifier: identifier.rawValue, sender: sender)
    }
}

extension UIButton {
    func setTitle(_ title: R.string, for state: UIControl.State) {
        setTitle(title.rawValue, for: state)
    }
}
class HomeViewController: UIViewController {

    override func viewDidLoad() {
        
        let img = UIImage.init(R.image.logo)
        let btn = UIButton(type: .custom)
        btn.setTitle(R.string.add, for: .normal)
        performSegue(withIdentifier: R.segue.login_main, sender: self)
        
    } 
}

enum R {
    
    enum image {
        static var logo = UIImage(named: "logo")
    }
    enum font {
        static func arial(_ size: CGFloat) -> UIFont? {
            UIFont(name: "Arial", size: size)
        }
    }
}


class HomeViewController: UIViewController {

    override func viewDidLoad() {
        
        let img = R.image.logo
        let font = R.font.arial(14)
  
        
    } 
}

• 更多优秀思路参考:
  R.swift
  SwiftGen