delegate使用注意：
1、協(xié)議繼承自NSObjectProtocol
2、弱引用delegate，防止代理對象無法釋放導(dǎo)致的循環(huán)引用

自定義Person類，設(shè)置代理

class Person: NSObject {
    
    weak var delegate: PersonDelegate?
    override init() {
        super.init()
        DispatchQueue.main.asyncAfter(deadline: .now()+1) {
            self.peopleLife()
            DispatchQueue.main.asyncAfter(deadline: .now()+1) {
                self.peopleRun()
            }
        }
    }
    func peopleLife() {
        delegate?.life()
    }
    func peopleRun() {
        delegate?.run()
    }
    deinit {
        print("Person deinit")
    }
}

protocol PersonDelegate: NSObjectProtocol {
    func life()
    func run()
}

SecViewController成為Person的代理：實(shí)現(xiàn)協(xié)議中的方法

class SecViewController: UIViewController, PersonDelegate {    
    func life() {
        print("vc-life")
    }
    func run() {
        view.backgroundColor = .purple
        print("vc-dismiss")
    }
    var per: Person?
    override func viewDidLoad() {
        super.viewDidLoad()
        
        per = Person()
        per?.delegate = self
        
    }
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        self.dismiss(animated: true) {
            
        }
    }
    deinit {
        print("sec deinit")
    }
}