createNotificationChannels.java

@TargetApi(Build.VERSION_CODES.O)
private void createNotificationChannels(AppConfig config) {
    if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.O &&
            config.getChannelGroups()!= null) {
        for (AppConfig.ChannelGroup cg: config.getChannelGroups()) {
            NotificationChannelGroup ncg =
                    new NotificationChannelGroup(cg.groupId, cg.groupName);
            notificationManager.createNotificationChannelGroup(ncg);

            for (AppConfig.Channel channel : cg.channels) {
                NotificationChannel notificationChannel =
                        new NotificationChannel(channel.channelId, channel.channelName, channel.importance);
                notificationChannel.setGroup(ncg.getId());
                notificationManager.createNotificationChannel(notificationChannel);
            }
        }
    }
}