下面这个方法是写在AppDelegate.m文件中的锁定屏幕的方法：

- (NSUInteger)application:(UIApplication *)application supportedInterfaceOrientationsForWindow:(UIWindow *)window

但是如果直接写这个方法会报下面的警告：

Conflicting return type in implementation of 'application:supportedInterfaceOrientationsForWindow:': 'UIInterfaceOrientationMask' (aka 'enum UIInterfaceOrientationMask') vs 'NSUInteger' (aka 'unsigned long')

解决方案如下：

#if __IPHONE_OS_VERSION_MAX_ALLOWED < __IPHONE_9_0

- (NSUInteger)application:(UIApplication *)application supportedInterfaceOrientationsForWindow:(UIWindow *)window

#else

- (UIInterfaceOrientationMask)application:(UIApplication *)application supportedInterfaceOrientationsForWindow:(UIWindow *)window

#endif

{

    return 返回想要的类型;

}