View Controller中可以添加多個(gè)sub view，在需要的時(shí)候顯示出來；

可以通過viewController(parent)中可以添加多個(gè)child viewController;來控制頁面中的sub view，降低代碼耦合度；

通過切換，可以顯示不同的view；，替代之前的addSubView的管理

//在parent view controller 中添加 child view controller

FirstViewController *firstViewController=[[FirstViewController alloc] initWithNibName:@"FirstViewController" bundle:nil];

[self addChildViewController:firstViewController];

SecondViewController *secondViewController=[[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];

[self addChildViewController:secondViewController];

ThirdViewController *thirdViewController=[[ThirdViewController alloc] initWithNibName:@"ThirdViewController" bundle:nil];

[self addChildViewController:thirdViewController];

[self.view? addSubview:thirdViewController.view];

// addChildViewController回調(diào)用[child willMoveToParentViewController:self] ，但是不會(huì)調(diào)用didMoveToParentViewController，所以需要顯示調(diào)用

[thirdViewController didMoveToParentViewController:self];

currentViewController=thirdViewController;

//切換child view controller

[self transitionFromViewController:currentViewController toViewController:firstViewController duration:4 options:UIViewAnimationOptionTransitionFlipFromLeft animations:^{

}? completion:^(BOOL finished) {

//......

}];

currentViewController=firstViewController;

//移除child view controller

// removeFromParentViewController在移除child前不會(huì)調(diào)用[self willMoveToParentViewController:nil] ，所以需要顯示調(diào)用

[currentViewController willMoveToParentViewController:nil];

[currentViewController removeFromSuperview];

[currentViewController removeFromParentViewController];