iOS 关于横竖屏问题
2020-08-13 本文已影响0人
GoldenChan
关于横竖屏相关方法的响应都是迷之存在，很难琢磨，搞的一头雾水。最近项目中正好遇到某个控制器需要横屏展示，查阅WWDC资料未发现关于orientation或者rotation相关资料。
只能通过实验与猜测大致了解其生命周期了。
首先，当前屏幕是否支持横竖屏旋转取决于当前window的支持方向。
设置window横竖屏的地方有两处，
第一处，通过工程->General->DeviceOrientation来勾选支持的方向
第二处，通过重写Appdelegate中的方法来设置当前window支持的方向
- (UIInterfaceOrientationMask)application:(UIApplication *)application supportedInterfaceOrientationsForWindow:(UIWindow *)window
那么问题来了，既然有两处都可以设置，那么最终取值以哪一个为准呢？
通过测试发现，如果两处都设置了，最终以第二种设置为（主要）判断依据；如果第二处未设置，则以第一处为准。
只有当前window支持某个方向的旋转，才能对控制器（如UIviewcontroller）进行相应方向的旋转并达到想要的效果（内容跟着转动）。
设置了可旋转的方向之后，就要对个别控制器做更细致的限制了，比如想让A控制只能竖屏，或者让B控制器只能横屏，就需要用到VC的扩展方法(系统自带的)
//是否允许旋转
- (BOOL)shouldAutorotate {
NSLog(@"%s",__FUNCTION__);
return YES;
}
//present时可支持的旋转方向（present时在supportedInterfaceOrientations前执行）
- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation {
NSLog(@"%s",__FUNCTION__);
if (_orientationMask & UIInterfaceOrientationMaskLandscapeLeft) {
return UIInterfaceOrientationLandscapeLeft;
}
return UIInterfaceOrientationPortrait;
}
//支持的旋转方向
- (UIInterfaceOrientationMask)supportedInterfaceOrientations {
NSLog(@"%s",__FUNCTION__);
if ([AppDelegate sharedInstance].supportLandscape) {
return _orientationMask | UIInterfaceOrientationMaskLandscapeLeft;
} else {
return UIInterfaceOrientationMaskPortrait;
}
}
旋转事件的传递顺序研究
通过创建一个新项目，页面布局如下：
download.png
分别自定义了UINavigationcontroller和UIviewcontroller，并重写了vc旋转相关的三个扩展方法，将UINavigationcontroller设置为window的rootviewcontroller
//appdelegate中添加的代码如下
@property(nonatomic, assign, getter=isSupportLandscape) BOOL supportLandscape;
+ (AppDelegate *)sharedInstance;
- (UIInterfaceOrientationMask)application:(UIApplication *)application supportedInterfaceOrientationsForWindow:(UIWindow *)window {
NSLog(@"%s",__FUNCTION__);
if (self.isSupportLandscape) {
return UIInterfaceOrientationMaskAllButUpsideDown;
} else {
return UIInterfaceOrientationMaskPortrait;
}
}
//自定义的nav
- (BOOL)shouldAutorotate {
NSLog(@"%s",__FUNCTION__);
return YES;
}
- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation {
NSLog(@"%s",__FUNCTION__);
if ([AppDelegate sharedInstance].supportLandscape) {
return UIInterfaceOrientationLandscapeLeft;
}
return UIInterfaceOrientationPortrait;
}
- (UIInterfaceOrientationMask)supportedInterfaceOrientations {
NSLog(@"%s",__FUNCTION__);
return UIInterfaceOrientationMaskAllButUpsideDown;
}
//自定义的vc
- (BOOL)shouldAutorotate {
NSLog(@"%s",__FUNCTION__);
return YES;
}
- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation {
NSLog(@"%s",__FUNCTION__);
if ([AppDelegate sharedInstance].supportLandscape) {
return UIInterfaceOrientationLandscapeLeft;
}
return UIInterfaceOrientationPortrait;
}
- (UIInterfaceOrientationMask)supportedInterfaceOrientations {
NSLog(@"%s",__FUNCTION__);
return UIInterfaceOrientationMaskAllButUpsideDown;
}
直接启动APP查看旋转方法调用情况如下：
2020-08-12 18:54:38.481 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.481 rotation[17319:3924945] -[NavVC supportedInterfaceOrientations]
2020-08-12 18:54:38.482 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.482 rotation[17319:3924945] -[NavVC supportedInterfaceOrientations]
2020-08-12 18:54:38.482 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.483 rotation[17319:3924945] -[NavVC supportedInterfaceOrientations]
2020-08-12 18:54:38.483 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.483 rotation[17319:3924945] -[NavVC supportedInterfaceOrientations]
2020-08-12 18:54:38.496 rotation[17319:3924945] -[NavVC viewWillAppear:]
2020-08-12 18:54:38.498 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.498 rotation[17319:3924945] -[NavVC supportedInterfaceOrientations]
2020-08-12 18:54:38.499 rotation[17319:3924945] -[NavVC shouldAutorotate]
2020-08-12 18:54:38.546 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.546 rotation[17319:3924945] -[NavVC supportedInterfaceOrientations]
2020-08-12 18:54:38.547 rotation[17319:3924945] -[NavVC shouldAutorotate]
2020-08-12 18:54:38.547 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.547 rotation[17319:3924945] -[NavVC supportedInterfaceOrientations]
2020-08-12 18:54:38.583 rotation[17319:3924945] -[ViewController viewWillAppear:]
2020-08-12 18:54:38.585 rotation[17319:3924945] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 18:54:38.585 rotation[17319:3924945] -[ViewController supportedInterfaceOrientations]
通过以上打印结果可以看出，APP启动时，调用顺序为APPdelegate的application:supportedInterfaceOrientationsForWindow: -> nav的supportedInterfaceOrientations -> nav的shouldAutorotate -> vc的supportedInterfaceOrientations
通过以上结果论证得出结论：APP在监听到旋转时，会首先通知window 并执行delegate中的supportedInterfaceOrientationsForWindow方法，然后通知rootviewcontroller并执行supportedInterfaceOrientations方法,最后通知栈顶vc并执行supportedInterfaceOrientations。
以上例子我们发现只调用了nav的shouldAutorotate，而栈顶vc的shouldAutorotate方法被忽略了，或许我们可以猜测出，是否能够旋转取决于vc的父容器即nav。
此时，我们手动旋转模拟器，看看打印结果如何?
2020-08-12 19:32:08.191 rotation[18013:3934444] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 19:32:08.191 rotation[18013:3934444] -[NavVC supportedInterfaceOrientations]
2020-08-12 19:32:08.191 rotation[18013:3934444] -[NavVC shouldAutorotate]
2020-08-12 19:32:08.191 rotation[18013:3934444] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 19:32:08.191 rotation[18013:3934444] -[NavVC supportedInterfaceOrientations]
2020-08-12 19:32:08.199 rotation[18013:3934444] -[NavVC shouldAutorotate]
2020-08-12 19:32:08.199 rotation[18013:3934444] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 19:32:08.200 rotation[18013:3934444] -[NavVC supportedInterfaceOrientations]
2020-08-12 19:32:08.202 rotation[18013:3934444] -[NavVC shouldAutorotate]
2020-08-12 19:32:08.202 rotation[18013:3934444] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 19:32:08.202 rotation[18013:3934444] -[NavVC supportedInterfaceOrientations]
通过以上打印结果可以看出，手动旋转APP时，调用顺序为APPdelegate的application:supportedInterfaceOrientationsForWindow: -> nav的supportedInterfaceOrientations -> nav的shouldAutorotate
即使，手动旋转手机，也没有调用vc的shouldAutorotate方法，甚至连vc的supportedInterfaceOrientations方法都没有调用，
据此可以猜测当被旋转的视图容器为uinavigationcontroller时，其vc内容是否能够旋转取决于nav的支持方向；即使我们设置vc的方向仅为横向，最终方向还是取决于nav的支持方向。
为了进一步验证猜想，我们点击push按钮，跳转到另一个只允许横屏的自定义vc（LandscapeRightVC），打印结果如下:
2020-08-12 20:08:45.697 rotation[20626:3970125] -[ViewController viewWillDisappear:]
2020-08-12 20:08:45.698 rotation[20626:3970125] -[LandscapeRightVC viewWillAppear:]
2020-08-12 20:08:45.698 rotation[20626:3970125] -[LandscapeRightVC switchToLandscapeRight]
2020-08-12 20:08:45.698 rotation[20626:3970125] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:08:45.698 rotation[20626:3970125] -[NavVC supportedInterfaceOrientations]
2020-08-12 20:08:45.698 rotation[20626:3970125] -[NavVC shouldAutorotate]
2020-08-12 20:08:45.699 rotation[20626:3970125] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:08:45.699 rotation[20626:3970125] -[NavVC supportedInterfaceOrientations]
2020-08-12 20:08:45.705 rotation[20626:3970125] -[NavVC shouldAutorotate]
2020-08-12 20:08:45.706 rotation[20626:3970125] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:08:45.706 rotation[20626:3970125] -[NavVC supportedInterfaceOrientations]
2020-08-12 20:08:45.714 rotation[20626:3970125] -[NavVC shouldAutorotate]
2020-08-12 20:08:45.715 rotation[20626:3970125] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:08:45.726 rotation[20626:3970125] -[NavVC supportedInterfaceOrientations]
通过打印可以看到只调用了LandscapeRightVC的旋转方向的方法，而supportedInterfaceOrientations、shouldAutorotate方法均未调用，但屏幕方向确实已经横屏了，之所以能够横屏时因为此时nav支持横屏方向，进一步验证了以上观点。
我们再将当前nav设置为只支持竖屏，并且点击present按钮，跳转到只支持横屏的vc看看打印情况：
2020-08-12 20:15:28.471 rotation[20923:3973796] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:15:28.471 rotation[20923:3973796] -[NavVC supportedInterfaceOrientations]
2020-08-12 20:15:28.472 rotation[20923:3973796] -[LandscapeRightVC preferredInterfaceOrientationForPresentation]
2020-08-12 20:15:28.472 rotation[20923:3973796] -[LandscapeRightVC supportedInterfaceOrientations]
2020-08-12 20:15:28.477 rotation[20923:3973796] -[NavVC shouldAutorotate]
2020-08-12 20:15:28.477 rotation[20923:3973796] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:15:28.477 rotation[20923:3973796] -[NavVC supportedInterfaceOrientations]
2020-08-12 20:15:28.477 rotation[20923:3973796] -[LandscapeRightVC shouldAutorotate]
2020-08-12 20:15:28.477 rotation[20923:3973796] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:15:28.478 rotation[20923:3973796] -[LandscapeRightVC supportedInterfaceOrientations]
2020-08-12 20:15:28.481 rotation[20923:3973796] -[ViewController viewWillDisappear:]
2020-08-12 20:15:28.482 rotation[20923:3973796] -[NavVC viewWillDisappear:]
2020-08-12 20:15:28.482 rotation[20923:3973796] -[LandscapeRightVC viewWillAppear:]
2020-08-12 20:15:28.500 rotation[20923:3973796] -[LandscapeRightVC switchToLandscapeRight]
2020-08-12 20:15:29.005 rotation[20923:3973796] -[NavVC shouldAutorotate]
2020-08-12 20:15:29.006 rotation[20923:3973796] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:15:29.006 rotation[20923:3973796] -[NavVC supportedInterfaceOrientations]
2020-08-12 20:15:29.007 rotation[20923:3973796] -[LandscapeRightVC shouldAutorotate]
2020-08-12 20:15:29.008 rotation[20923:3973796] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-12 20:15:29.008 rotation[20923:3973796] -[LandscapeRightVC supportedInterfaceOrientations]
执行顺序大致是：
[AppDelegate application:supportedInterfaceOrientationsForWindow:] ->
[NavVC supportedInterfaceOrientations] ->
[LandscapeRightVC preferredInterfaceOrientationForPresentation] ->
[LandscapeRightVC supportedInterfaceOrientations] ->
[NavVC shouldAutorotate] ->
[LandscapeRightVC shouldAutorotate] ->
[LandscapeRightVC supportedInterfaceOrientations]
image.png
通过present后确实已经横屏，得出结论，如果是从vc中present出来的视图，即使上一层nav不支持横屏，最终屏幕旋转方向取决于被present出来的视图容器所支持的屏幕方向。
总结：
屏幕旋转的需求大概有两种：
1.通过翻转手机自动旋转内容
2.项目只支持竖屏或横屏模式，个别页面需要强制横屏或竖屏展示
以上两种需求其实都可以通过 设置appdelegate -> nav或tabbar 来支持需要旋转的方向，唯一区别在于需求1中无需强制执行代码来旋转方向，属于被动旋转；而需求2则要在需要旋转到固定方向的vc中做强制旋转。
//通过代码强制旋转
//为了防止plus及ipad机型自带桌面旋转功能时，横屏失败，所以先强制旋转到其他方向，再设置横屏才会有效果
[[UIDevice currentDevice] setValue:@(UIDeviceOrientationFaceDown) forKey:@"orientation"];
[[UIDevice currentDevice] setValue:@(UIDeviceOrientationLandscapeRight) forKey:@"orientation"];
那么对于一个项目中个别页面需要横屏时，我们大致可以进行如下写法：
//AppDelegate中
@property(nonatomic, assign, getter=isSupportLandscape) BOOL supportLandscape;
+ (AppDelegate *)sharedInstance {
return (AppDelegate *)[UIApplication sharedApplication].delegate;
}
- (UIInterfaceOrientationMask)application:(UIApplication *)application supportedInterfaceOrientationsForWindow:(UIWindow *)window {
NSLog(@"%s",__FUNCTION__);
if (self.isSupportLandscape) {
return UIInterfaceOrientationMaskAllButUpsideDown;
} else {
return UIInterfaceOrientationMaskPortrait;
}
}
//自定义的Navigationcontroller中
//虽然nav是控制旋转的主要因素，但为了保持和最上层vc的旋转方向一致，这里统一取topvc的方向设置
- (BOOL)shouldAutorotate {
NSLog(@"%s",__FUNCTION__);
return [self.viewControllers.lastObject shouldAutorotate];
}
- (UIInterfaceOrientationMask)supportedInterfaceOrientations {
NSLog(@"%s",__FUNCTION__);
return [self.viewControllers.lastObject supportedInterfaceOrientations];
}
- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation {
NSLog(@"%s",__FUNCTION__);
return [self.viewControllers.lastObject preferredInterfaceOrientationForPresentation];
//需要横屏展示的vc中
@interface LandscapeRightVC ()
@property (nonatomic, assign) UIInterfaceOrientationMask orientationMask;
@end
@implementation LandscapeRightVC
- (instancetype)init {
self = [super init];
if (self) {
_orientationMask = UIInterfaceOrientationMaskLandscapeLeft|UIInterfaceOrientationMaskPortrait;
}
return self;
}
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
self.title = NSStringFromClass([self class]);
self.view.backgroundColor = [UIColor whiteColor];
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[AppDelegate sharedInstance].supportLandscape = YES;
NSLog(@"%s",__FUNCTION__);
[self switchToLandscapeRight];
}
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
[AppDelegate sharedInstance].supportLandscape = NO;
NSLog(@"%s",__FUNCTION__);
[self switchToLandscapePortrait];
}
- (BOOL)shouldAutorotate {
NSLog(@"%s",__FUNCTION__);
return YES;
}
- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation {
NSLog(@"%s",__FUNCTION__);
//这里加入[AppDelegate sharedInstance].supportLandscape判断，是为了防止appdelegate中不支持目标方向，而产生Supported orientations has no common orientation with the application的错误
if ([AppDelegate sharedInstance].supportLandscape) {
if (_orientationMask & UIInterfaceOrientationMaskLandscapeLeft) {
return UIInterfaceOrientationLandscapeLeft;
}
}
return UIInterfaceOrientationPortrait;
}
- (UIInterfaceOrientationMask)supportedInterfaceOrientations {
NSLog(@"%s",__FUNCTION__);
//这里加入[AppDelegate sharedInstance].supportLandscape判断，是为了防止appdelegate中不支持目标方向，而产生Supported orientations has no common orientation with the application的错误
if ([AppDelegate sharedInstance].supportLandscape) {
return _orientationMask | UIInterfaceOrientationMaskLandscapeLeft;
} else {
return UIInterfaceOrientationMaskPortrait;
}
}
// 手动设置横屏
- (void)switchToLandscapeRight {
NSLog(@"%s",__FUNCTION__);
_orientationMask = UIInterfaceOrientationMaskLandscapeLeft;
//为了防止plus及ipad机型自带桌面旋转功能时，横屏失败，所以先强制旋转到其他方向，再设置横屏才会有效果
[[UIDevice currentDevice] setValue:@(UIDeviceOrientationFaceDown) forKey:@"orientation"];
[[UIDevice currentDevice] setValue:@(UIDeviceOrientationLandscapeRight) forKey:@"orientation"];
}
// 手动设置竖屏
- (void)switchToLandscapePortrait {
NSLog(@"%s",__FUNCTION__);
_orientationMask = UIInterfaceOrientationMaskPortrait;
[[UIDevice currentDevice] setValue:@(UIDeviceOrientationFaceDown) forKey:@"orientation"];
[[UIDevice currentDevice] setValue:@(UIDeviceOrientationPortrait) forKey:@"orientation"];
}
延伸：测试一下UITabbarController是如何响应的
假如将rootviewcontroller设置为tabbar，并将tabbar设置为只支持竖屏，而将其中一个item设置为LandscapeRightVC，打印结果如下：
2020-08-13 18:19:59.440 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.440 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.443 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.443 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.443 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.444 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.444 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.444 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.453 rotation[84659:4616469] -[LandscapeRightVC viewWillAppear:]
2020-08-13 18:19:59.453 rotation[84659:4616469] -[LandscapeRightVC switchToLandscapeRight]
2020-08-13 18:19:59.453 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.454 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.454 rotation[84659:4616469] -[CusTabViewController shouldAutorotate]
2020-08-13 18:19:59.454 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.454 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.455 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.455 rotation[84659:4616469] -[LandscapeRightVC supportedInterfaceOrientations]
2020-08-13 18:19:59.456 rotation[84659:4616469] -[CusTabViewController shouldAutorotate]
2020-08-13 18:19:59.456 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.457 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.457 rotation[84659:4616469] -[CusTabViewController shouldAutorotate]
2020-08-13 18:19:59.457 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.457 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.458 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.458 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
2020-08-13 18:19:59.458 rotation[84659:4616469] -[AppDelegate application:supportedInterfaceOrientationsForWindow:]
2020-08-13 18:19:59.458 rotation[84659:4616469] -[CusTabViewController supportedInterfaceOrientations]
可以看到tabbar的传递顺序与nav类似，并且属于是视图容器，假如tabbar不支持横屏，那么子控制器无论如何旋转都不会有效
顺便提一提UIDeviceOrientation（设备方向）和UIInterfaceOrientation（UI方向）的区别
typedef NS_ENUM(NSInteger, UIInterfaceOrientation) {
UIInterfaceOrientationUnknown = UIDeviceOrientationUnknown,
UIInterfaceOrientationPortrait = UIDeviceOrientationPortrait,
UIInterfaceOrientationPortraitUpsideDown = UIDeviceOrientationPortraitUpsideDown,
UIInterfaceOrientationLandscapeLeft = UIDeviceOrientationLandscapeRight,
UIInterfaceOrientationLandscapeRight = UIDeviceOrientationLandscapeLeft
} API_UNAVAILABLE(tvos);
typedef NS_ENUM(NSInteger, UIDeviceOrientation) {
UIDeviceOrientationUnknown,
UIDeviceOrientationPortrait, // Device oriented vertically, home button on the bottom
UIDeviceOrientationPortraitUpsideDown, // Device oriented vertically, home button on the top
UIDeviceOrientationLandscapeLeft, // Device oriented horizontally, home button on the right
UIDeviceOrientationLandscapeRight, // Device oriented horizontally, home button on the left
UIDeviceOrientationFaceUp, // Device oriented flat, face up
UIDeviceOrientationFaceDown // Device oriented flat, face down
} API_UNAVAILABLE(tvos);
可以看到横向的方向命名是相反的，在使用时需要注意
思考：如果rootviewcontroller是nav，而nav的root是tabbar，tabbar的item又是nav 那么子视图的旋转又是如何受约束的呢？我猜应该是， 取当前栈顶容器（如果是push，则取当前栈顶容器nav，如果是present，则取当前present栈顶中的容器nav或vc，且present的视图不受parent视图的横竖屏限制）
