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;
}
