2015年12月10日
Stanford CS193p第八课 View Controller Lifecycle, Autolayout
View Controller Lifecycle
View Controller Lifecycle是什么
即一系列发送至View Controller消息的生命周期为什么要关心View Controller Lifecycle
通常我们会在项目的子类中腹泻这些发送给View Controller 的消息,来了解我们的应用正在干什么.
我们可能希望做一些决定或其他操作在View Controller 生命周期的某一个特定时刻View Controller Lifecycle如何工作
1.从StoryBoard中得到实例化
2.得到awakeFromNib
3.segue准备发生
4.outlets将被系统设置
5.viewDidLoad方法将被调用
6.View将会出现并且消失(viewWillAppear,ViewDidAppear,viewWillDisappear,viewDidDisappear)
7.随着视图控制器的几何变化(屏幕翻转)viewWillLayoutSubview方法被调用,然后是viewDidLayoutSubview.这也许会发生很多次
8.如果可用内存很小,可能会得到内存警报(didReceiveMemoryWarning)viewDidLoad
在viewDidLoad中初始化视图代码是最好的方式,因为在viewDidLoad进行加载前,segue已经准备完毕、outlets的设定已经完成.不要忘记调用super. viewDidLoad
通常我们在viewDidLoad中做的是更新UI,一旦我们的Model发生了改变,我们的Model会在属性观察器中更新UI.所以最好在viewDidLoad中进行UI更新注意:不要在viewDidLoad中做与几何位置相关的操作.
Autolayout
Autolayout主要是通过StoryBoard来进行实现, Autolayout还是要在自己不断的使用和调试中积累经验,在此不做过多的叙述.
AutolayoutDemo
本课跟随教程实现了一个小登录器的项目,主要是调试登录后图片的自动布局及旋转后的布局,大多数布局由StoryBoard上的操作完成,图片的自动布局有代码来完成.DEMO的代码如下
//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
}()
}
