iOS 注册通知失败 with an alert but haven't received permission from the user to display alerts

在iOS8以后使用通知要先注册

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    if ([UIApplication instancesRespondToSelector:@selector(registerUserNotificationSettings:)]) {
        [application registerUserNotificationSettings:[UIUserNotificationSettings settingsForTypes:UIUserNotificationTypeAlert |UIUserNotificationTypeBadge|UIUserNotificationTypeSound categories:nil]];
    }
    return YES;
}