IOS之Lifecycle与Autolayout

//viewController
import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var LogingField: UITextField!

    @IBOutlet weak var passwordField: UITextField!

    @IBOutlet weak var passwordLabel: UILabel!

    @IBOutlet weak var nameLabel: UILabel!

    @IBOutlet weak var companyLabel: UILabel!

    @IBOutlet weak var imageView: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
        updateUI()
    }

    var secure = false {
        didSet {
            updateUI()
        }
    }

    var loggedInUser: User? {
        didSet {
            updateUI()
        }
    }

    private func updateUI() {
        passwordField.secureTextEntry = secure //设置密码框的加密输入,为true时密码被替换为***,为false时直接显示输入值
        passwordLabel.text = secure ? "secured Password" : "Password"
        nameLabel.text = loggedInUser?.name
        companyLabel.text = loggedInUser?.company
        image = loggedInUser?.image
    }

    @IBAction func toggleSecurity(sender: UIButton) { //改变密码显示方式
        secure = !secure
    }


    @IBAction func login() {
        loggedInUser = User.login(LogingField.text ?? "", password: passwordField.text ?? "")
    }

    var image: UIImage? {
        get {
            return imageView.image
        }
        set {
            imageView.image = newValue
            if let constrainedView = imageView {
                if let newImage = newValue { //设置约束
                    aspectRatioConstraint = NSLayoutConstraint(item: constrainedView, attribute: .Width, relatedBy: .Equal, toItem: constrainedView, attribute: .Height, multiplier: newImage.aspectRatio, constant:0)
                }else {
                    aspectRatioConstraint = nil
                }
            }
        }
    }


    //NSLayoutConstraint为所有约束的class
    var aspectRatioConstraint: NSLayoutConstraint? {
        willSet { //在未设置前清除已存在的约束
            if let existingConstraint = aspectRatioConstraint {
                view.removeConstraint(existingConstraint)
            }
        }
        didSet { //设置约束
            if let newConstraint = aspectRatioConstraint {
                view.addConstraint(newConstraint)
            }
        }
    }

}

//对Model进行扩展,添加image
extension User {
    var image: UIImage? {
        if let image = UIImage(named: login) {
              return image
        } else {
            return UIImage(named: "unknown_user")
        }

    }
}

//保证图片宽高比与原图一致
extension UIImage {
    var aspectRatio: CGFloat {
        return size.height != 0 ? size.width / size.height : 0
    }
}

//Model
import Foundation

struct User {
    let name: String
    let company: String
    let login: String
    let password: String

    static func login(login: String, password: String) -> User? {
        if let user = datebase[login] {
            if user.password == password {
                return user
            }
        }
        return nil
    }
    //数据库
    static let datebase: Dictionary<String, User> = {
        var theDatabase = Dictionary<String, User>()
        for user in [
            User(name: "John Appleseed", company: "Apple", login: "japple", password: "foo"),
            User(name: "Madisom Bumgarner", company: "World Champion San Francisco Giants", login: "madbum", password: "foo"),
            User(name: "John Hennessy", company: "Stanford", login: "hennessy", password: "foo"),
            User(name: "Bad Guy", company: "Criminals Inc", login: "baddie", password: "foo")
            ] {
                theDatabase[user.login] = user
        }
        return theDatabase
    }()

}