/使用在iOS8 及其以上的系统/

 UIUserNotificationSettings *setting = [[UIApplication sharedApplication] currentUserNotificationSettings];
        if (UIUserNotificationTypeNone == setting.types) {
            NSLog(@"推送关闭");
        }else{
            NSLog(@"推送打开");
        }

如果用户没有开启通知 需要跳转到应用的设置中设置开启通知

 [[UIApplication sharedApplication] openURL:[NSURL URLWithString:UIApplicationOpenSettingsURLString]];