一、介绍
老规矩先看SDK
Container view controllers are a critical part of iOS app design. They allow you todecompose your app into smaller and 易做图r parts, each controlled by a viewcontroller dedicated to that task. Containers allow these view controllers towork together to present a seamless inte易做图ce.
就是说，容器型的viewController能够把app分为很多小而简单的部分来管理，允许他们一起无缝的展示用户界面。
其实应该已经接触过了一些container，viewcontrollers 经常很container一起工作。例如NavigationController、TabBar就是几个典型的container，它可以管理很多view controller。这次就来小小的研究一下customer container。
二、API
addChildViewController:
removeFromParentViewController
transitionFromViewController:toViewController:duration:options:animations:completion:
willMoveToParentViewController:
didMoveToParentViewController:
基本上就是这几个方法。
三、用法
添加子节点
[cpp]
//定义child
First *first = [[Firstalloc]initWithNibName:@"First"bundle:nil];
//添加child
[selfaddChildViewController:first];
获得子节点
[cpp]
[self.childViewControllersobjectAtIndex:0];
添加进入的子节点是有顺序的，从0开始。
获取子节点的个数
[cpp]
self.childViewControllers.count
子节点的切换
使用下面的方法：
- (void)transitionFromViewController:(UIViewController *)fromViewControllertoViewController:(UIViewController *)toViewController duration:(NSTimeInterval)duration options:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion
参数：
fromViewController：必须是当前正在显示的子节点
toViewController：是当前没有被显示的子节点
duration：动画的时长，以秒为单位，如果设置为0则不显示动画。
Options：选择怎么样去表现动画，UIViewAnimationOptions是一个枚举，里面包含了很多表现动画的方式，例如UIViewAnimationOptionTransitionFlipFromBottom从底部翻滚上来。
Animations：在这里可以添加动画，用于改变view。
Completion：动画完成之后会调用的闭包，YES为动画完成，NO为动画被跳过了。
把child移除parent
removeFromParentViewController方法
[cpp]
[[self.childViewControllersobjectAtIndex:0]removeFromParentViewController];//移出第一个child
willMoveToParentViewController:与didMoveToParentViewController:
有点奇怪，我本以为这两个方法都应该是当child被加入或者移出parent的时候被调用，按照willMoveToParentViewController到didMoveToParentViewController的顺序。
但是测试结果有些奇怪，当child被加入到parent的时候只调用了willMoveToParentViewController，而当child被移出parent的时候只调用了didMoveToParentViewController方法，不解。看SDK。
willMoveToParentViewController:
Called just before the view controller is added or removed from a container viewcontroller.
也就是说被在添加或者移出前都会调用这个方法，继续看。
Your view controller can override this method when it needs to know thatit has been added to a container.
If you are implementing your own container view controller, it must callthewillMoveToParentViewController: method of the child view controller before calling theremoveFromParentViewController method, passing in a parent value ofnil.
意思是，当你实现自己的container viewcontroller的时候，在使用removeFromParentViewController方法移出child之前，首先要手动调用willMoveToParentViewController,并且设置parent参数为nil才行。所以说child移出的时候根本不会自动调用willMoveToParentViewController==。。。
When your custom container calls the addChildViewController: method, it automatically calls the willMoveToParentViewController: method of the view controller to be added as a child before adding it.
而当调用addChildViewController添加child的时候则会被自动调用。
再来看看didMoveToParentViewController。
didMoveToParentViewController:
Calledafter the view controller is added or removed from a container view controller.
当子节点已经被添加或者移出容器的时候被调用。
Discussion
Your view controller can override this method when it wants to react tobeing added to a container.
If you are implementing your own container view controller, it must callthedidMoveToParentViewController: method of the child view controller after the transition to the newcontroller is complete or, if there is no transition, immediately after callingtheaddChildViewController: method.
必须在从一个child到另一个child的转换之后（transitionFromViewController方法），手动调用didMoveToParentViewController方法。如果没有转化则需要在addChildViewController之后立即调用。
The removeFromParentViewController method automatically calls thedidMoveToParentViewController: method of the child view controller after it removes thechild.
同理，didMoveToParentViewController也只会在子节点被移出时自动调用。
