仓库github/DrawController()
是一个Swift语言编写的抽屉库。它可以传入一个中心视图控制器，一个左侧视图控制器，并由一个MaxDrawerWidth属性。创建完毕后，中心视图控制器的视图内容占据全部屏幕；当执行打开抽屉的函数时，整个中心控制的视图内容一起向右平移MaxDrawerWidth这么宽，并且显示左侧视图控制器的内容到屏幕上，内容占满屏幕，但是宽度不超过MaxDrawerWidth指定的值。研究此代码库的时候，发现它是一个很好的解说Container View Controller[] 概念的例子。这里面：
- 类DrawerController就是一个Container View Controller
- 其他的视图控制器就是Child View Controller
- 第一个类和其他类构成了父子关系
- 视图控制器内的视图其实都是放置到DrawerController.view之内的
我把此库内的关于动画和手势的代码全部去掉，专门留下特定于这些控制器交互的代码留下。从1000多行的代码抽取出来247行的代码如下：
import UIKit var drawerController : DrawerPage? @UIApplicationMain class AppDelegate: UIResponder, UIApplicationDelegate { var window : UIWindow? func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool { window = UIWindow() drawerController = DrawerPage() window!.rootViewController = drawerController window!.rootViewController!.view.backgroundColor = .blue window!.makeKeyAndVisible() return true } } class DrawerPage : DrawerBase{ init(){ super.init(CenterPage(),LeftPage()) } // 哄编译器开心的代码 required init?(coder aDecoder: NSCoder) { super.init(coder: aDecoder) } } class DrawerBase : DrawerController{ init(_ center : UIViewController,_ left : UIViewController){ super.init(centerViewController: center, leftDrawerViewController: left) } // 从入门到入门： // 1. What exactly is init coder aDecoder? // 2. What does the question mark means in public init?(coder aDecoder: NSCoder)? required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") } } class LeftPage: UIViewController { var count = 0 var label : UILabel! override func viewDidLoad() { super.viewDidLoad() self.view.backgroundColor = .white label = UILabel() label.frame = CGRect(x: 100, y: 100, width: 120, height: 50) label.text = "Left" view.addSubview(label) let button = UIButton(type: .system) button.frame = CGRect(x: 120, y: 150, width: 120, height: 50) button.setTitle("Close",for: .normal) button.addTarget(self, action: #selector(buttonAction(_:)), for: .touchUpInside) view.addSubview(button) } @objc func buttonAction(_ sender:UIButton!){ drawerController?.toggleLeftDrawerSide(animated: true, completion: nil) } } class CenterPage: UIViewController { var label : UILabel! override func viewDidLoad() { super.viewDidLoad() self.view.backgroundColor = .white label = UILabel() label.frame = CGRect(x: 100, y: 100, width: 120, height: 50) label.text = "Center" view.addSubview(label) let button = UIButton(type: .system) button.frame = CGRect(x: 120, y: 150, width: 120, height: 50) button.backgroundColor = .blue button.setTitle("Left Page Drawer",for: .normal) button.addTarget(self, action: #selector(buttonAction(_:)), for: .touchUpInside) view.addSubview(button) } @objc func buttonAction(_ sender:UIButton!){ drawerController?.toggleLeftDrawerSide(animated: true, completion: nil) } @objc func buttonAction1(_ sender:UIButton!){// drawerController?.toggleRightDrawerSide(animated: true, completion: nil) } } // code imple open class DrawerController: UIViewController { fileprivate var _centerViewController: UIViewController? fileprivate var _leftDrawerViewController: UIViewController? fileprivate var _leftDrawerWidth = DrawerDefaultWidth open var centerViewController: UIViewController? { get { return self._centerViewController } } open var leftDrawerViewController: UIViewController? { get { return self._leftDrawerViewController } } open var leftDrawerWidth: CGFloat { get { return self._leftDrawerWidth } } open var shadowRadius = DrawerDefaultShadowRadius open var shadowOpacity = DrawerDefaultShadowOpacity fileprivate lazy var childControllerContainerView: UIView = { let a = UIView(frame: self.view.bounds) self.view.addSubview(a) return a }() fileprivate lazy var centerContainerView: DrawerCenterContainerView = { let centerFrame = self.childControllerContainerView.bounds let centerContainerView = DrawerCenterContainerView(frame: centerFrame) centerContainerView.autoresizingMask = [.flexibleWidth, .flexibleHeight] centerContainerView.backgroundColor = UIColor.clear self.childControllerContainerView.addSubview(centerContainerView) return centerContainerView }() open fileprivate(set) var openSide: DrawerSide = .center { didSet { if self.openSide == .center { self.leftDrawerViewController?.view.isHidden = true } self.setNeedsStatusBarAppearanceUpdate() } } public required init?(coder aDecoder: NSCoder) { super.init(coder: aDecoder) } override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) { super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil) } public init(centerViewController: UIViewController, leftDrawerViewController: UIViewController?) { super.init(nibName: nil, bundle: nil) self.setCenter(centerViewController) self.setDrawer(leftDrawerViewController,for:.left) } fileprivate func childViewController(for drawerSide: DrawerSide) -> UIViewController? { var childViewController: UIViewController? switch drawerSide { case .left: childViewController = self.leftDrawerViewController case .center: childViewController = self.centerViewController } return childViewController } fileprivate func sideDrawerViewController(for drawerSide: DrawerSide) -> UIViewController? { var sideDrawerViewController: UIViewController? if drawerSide != .center { sideDrawerViewController = self.childViewController(for: drawerSide) } return sideDrawerViewController } fileprivate func updateShadowForCenterView() { self.centerContainerView.layer.masksToBounds = false self.centerContainerView.layer.shadowRadius = shadowRadius self.centerContainerView.layer.shadowOpacity = shadowOpacity if let shadowPath = centerContainerView.layer.shadowPath { let currentPath = shadowPath.boundingBoxOfPath if currentPath.equalTo(centerContainerView.bounds) == false { centerContainerView.layer.shadowPath = UIBezierPath(rect: centerContainerView.bounds).cgPath } } else { self.centerContainerView.layer.shadowPath = UIBezierPath(rect: self.centerContainerView.bounds).cgPath } } open func toggleLeftDrawerSide(animated: Bool, completion: ((Bool) -> Void)?) { self.toggleDrawerSide(.left, animated: animated, completion: completion) } open func toggleDrawerSide(_ drawerSide: DrawerSide, animated: Bool, completion: ((Bool) -> Void)?) { assert({ () -> Bool in return drawerSide != .center }(), "drawerSide cannot be .None") if self.openSide == DrawerSide.center { self.openDrawerSide(drawerSide,completion: completion) } else { if (drawerSide == DrawerSide.left && self.openSide == DrawerSide.left) { self.closeDrawer(animated: animated, completion: completion) } else if completion != nil { completion!(false) } } } fileprivate func openDrawerSide(_ drawerSide: DrawerSide,completion: ((Bool) -> Void)?) { assert({ () -> Bool in return drawerSide != .center }(), "drawerSide cannot be .None") if let vc = self.leftDrawerViewController{ vc.view.isHidden = false var newFrame: CGRect newFrame = view.frame newFrame.size.width = _leftDrawerWidth vc.view.frame = newFrame // vc.view.frame = vc.evo_visibleDrawerFrame } func panRight(_ view : UIView,_ value : CGFloat){ var newFrame: CGRect newFrame = view.frame newFrame.origin.x = value view.frame = newFrame } panRight(centerContainerView, _leftDrawerWidth) self.openSide = drawerSide } fileprivate func setDrawer(_ vc: UIViewController?, for drawerSide: DrawerSide) { assert({ () -> Bool in return drawerSide != .center }(), "drawerSide cannot be .None") let currentSideViewController = self.sideDrawerViewController(for: drawerSide) if currentSideViewController == vc { return } self._leftDrawerViewController = vc if vc != nil { self.addChildViewController(vc!) vc!.didMove(toParentViewController: self) self.childControllerContainerView.addSubview(vc!.view) self.childControllerContainerView.sendSubview(toBack: vc!.view) vc!.view.isHidden = true } } fileprivate func setCenter(_ vc: UIViewController?) { self._centerViewController = vc if vc != nil { self.addChildViewController(vc!) vc!.didMove(toParentViewController: self) self.centerContainerView.addSubview(vc!.view) self._centerViewController!.view.frame = self.centerContainerView.bounds self.updateShadowForCenterView() } } open func closeDrawer(animated: Bool, completion: ((Bool) -> Void)?) { let newFrame = self.childControllerContainerView.bounds self.setNeedsStatusBarAppearanceUpdate() self.centerContainerView.frame = newFrame self.openSide = .center } open override func viewDidLoad() { super.viewDidLoad() self.view.backgroundColor = UIColor.black } static let DrawerDefaultWidth: CGFloat = 210.0 //280.0 static let DrawerDefaultShadowRadius: CGFloat = 10.0 static let DrawerDefaultShadowOpacity: Float = 0.8 typealias DrawerCenterContainerView = UIView public enum DrawerSide: Int { case center case left } }复制代码 这里的代码，很关键的是在DrawerController内的view中，创建了一个子视图叫做childControllerContainerView，其内在创建一个子视图centerContainerView，它们几个的大小都是屏幕大小，视图层次为：
--view----childControllerContainerView------centerContainerView复制代码
并约定好:
- 全部的Center View Controller的视图全部放置到centerContainerView内
- 全部的left View Controller和right View Controller的视图全部放置到centerContainerView内
- left View Controller和right View Controller的视图放置完毕后，需要首先隐藏起来，并且sendToBack，保证它是不可见的，也不会遮挡任何Center View Controller的内容
这样当指定打开抽屉函数时，centerContainerView整体平移，如果打开左边的抽屉，就向右移动，反之亦然。从而Center View Controller的视图也就跟着平移。并同时把抽屉视图（left View Controller和right View Controller的视图）显示出来，但是宽度不超过MaxDrawerWidth。
通过以上分析，可以加强对Container View Controller概念的理解。