if ([[UIDevice currentDevice].systemVersion floatValue] >= 10.0) 运行环境判断；
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_10_0 编译器、开发环境支持；
部署环境支持；
UNUserNotificationCenter *center = [UNUserNotificationCenter currentNotificationCenter]
在低于库版本的运行环境运行时，center返回值为nil；
结论：
1）在对象或类符号不存在时，动态库没有任何存在，返回值为nil；
2）当一个类的接口存在跨系统级别的函数存在时，因为类或对象存在，函数符号不存在，所以存在崩溃的情况。
- (void)registerRemoteNotification {
if ([[UIDevice currentDevice].systemVersion floatValue] >= 10.0) {
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_10_0 // Xcode 8编译会调用
UNUserNotificationCenter *center = [UNUserNotificationCenter currentNotificationCenter];
center.delegate = self;
[center requestAuthorizationWithOptions:(UNAuthorizationOptionBadge | UNAuthorizationOptionSound | UNAuthorizationOptionAlert | UNAuthorizationOptionCarPlay) completionHandler:^(BOOL granted, NSError *_Nullable error) {
if (!error) {
NSLog(@"request authorization succeeded!");
}
}];
[[UIApplication sharedApplication] registerForRemoteNotifications];
#endif
} else if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0) {
UIUserNotificationType types = (UIUserNotificationTypeAlert | UIUserNotificationTypeSound | UIUserNotificationTypeBadge);
UIUserNotificationSettings *settings = [UIUserNotificationSettings settingsForTypes:types categories:nil];
[[UIApplication sharedApplication] registerUserNotificationSettings:settings];
[[UIApplication sharedApplication] registerForRemoteNotifications];
} else {
UIRemoteNotificationType apn_type = (UIRemoteNotificationType)(UIRemoteNotificationTypeAlert |
UIRemoteNotificationTypeSound |
UIRemoteNotificationTypeBadge);
[[UIApplication sharedApplication] registerForRemoteNotificationTypes:apn_type];
}
}