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iOS 关于横竖屏问题

iOS 关于横竖屏问题

作者: GoldenChan | 来源:发表于2020-08-13 11:33 被阅读0次

    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）

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