仓库github/DrawController(github.com/sascha/Draw…)
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[developer.apple.com/library/con…] 概念的例子。这里面：

1. 类DrawerController就是一个Container View Controller
2. 其他的视图控制器就是Child View Controller
3. 第一个类和其他类构成了父子关系
4. 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 UIKitvar drawerController : DrawerPage?@UIApplicationMainclass AppDelegate: UIResponder, UIApplicationDelegate {var window : UIWindow?func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {window = UIWindow()drawerController = DrawerPage()window!.rootViewController = drawerControllerwindow!.rootViewController!.view.backgroundColor = .bluewindow!.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 = 0var label : UILabel!override func viewDidLoad() {super.viewDidLoad()self.view.backgroundColor = .whitelabel   = 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 = .whitelabel   = 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 = .bluebutton.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 impleopen class DrawerController: UIViewController {fileprivate var _centerViewController: UIViewController?fileprivate var _leftDrawerViewController: UIViewController?fileprivate var _leftDrawerWidth = DrawerDefaultWidthopen 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 = DrawerDefaultShadowRadiusopen var shadowOpacity = DrawerDefaultShadowOpacityfileprivate 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.boundslet centerContainerView = DrawerCenterContainerView(frame: centerFrame)centerContainerView.autoresizingMask = [.flexibleWidth, .flexibleHeight]centerContainerView.backgroundColor = UIColor.clearself.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.leftDrawerViewControllercase .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 = falseself.centerContainerView.layer.shadowRadius = shadowRadiusself.centerContainerView.layer.shadowOpacity = shadowOpacityif let shadowPath = centerContainerView.layer.shadowPath {let currentPath = shadowPath.boundingBoxOfPathif 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 inreturn 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 inreturn drawerSide != .center}(), "drawerSide cannot be .None")if let vc = self.leftDrawerViewController{vc.view.isHidden = falsevar newFrame: CGRectnewFrame = view.framenewFrame.size.width = _leftDrawerWidthvc.view.frame = newFrame//            vc.view.frame = vc.evo_visibleDrawerFrame}func panRight(_ view : UIView,_ value : CGFloat){var newFrame: CGRectnewFrame = view.framenewFrame.origin.x = valueview.frame = newFrame}panRight(centerContainerView, _leftDrawerWidth)self.openSide = drawerSide}fileprivate func setDrawer(_ vc: UIViewController?, for drawerSide: DrawerSide) {assert({ () -> Bool inreturn drawerSide != .center}(), "drawerSide cannot be .None")let currentSideViewController = self.sideDrawerViewController(for: drawerSide)if currentSideViewController == vc {return}self._leftDrawerViewController = vcif 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 = vcif vc != nil {self.addChildViewController(vc!)vc!.didMove(toParentViewController: self)self.centerContainerView.addSubview(vc!.view)self._centerViewController!.view.frame = self.centerContainerView.boundsself.updateShadowForCenterView()}}open func closeDrawer(animated: Bool, completion: ((Bool) -> Void)?) {let newFrame = self.childControllerContainerView.boundsself.setNeedsStatusBarAppearanceUpdate()self.centerContainerView.frame = newFrameself.openSide = .center}open override func viewDidLoad() {super.viewDidLoad()self.view.backgroundColor = UIColor.black}static let DrawerDefaultWidth: CGFloat = 210.0 //280.0static let DrawerDefaultShadowRadius: CGFloat = 10.0static let DrawerDefaultShadowOpacity: Float = 0.8typealias  DrawerCenterContainerView =  UIViewpublic enum DrawerSide: Int {case centercase 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:

1. 全部的Center View Controller的视图全部放置到centerContainerView内
2. 全部的left View Controller和right View Controller的视图全部放置到centerContainerView内
3. 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。