What is the "Uncategorized" Android Notification Channel and when does it appear?

Question

While transitioning an application to Android O, I have noticed a strange thing. Sometimes my foreground service notification goes into a channel that I have not made, called "Uncategorized". I have no idea how or when this happens.

The channels are always created before the notifications start being posted, and the ID of the channel is correct. I have tried putting in a random String as the channel ID to see if I could reproduce the issue, but the notification just doesn't get posted in that case. So it seems to be some weird case when the channel was already created before.

This is the channel's page:

And this is the channel appearing in the list of all channels of the app (note, I have removed the icon for privacy reasons).

Does anyone have any experience with this and could they explain when this can happen? Unfortunately, I found no documentation regarding this, and heard nothing about it in the Google I/O talks.

Answer 1

I think this is what happens if a part of your app does not support notification channel it seems.

Specifically in our case, if a SDK of ours is notification channel capable, but an app targets 25 and uses legacy features. We will always have legacy app notification go to that Uncategorized channel.

I can imagine there are other cases where the OS decides you need this channel because the OS thinks not everything is migrated properly. Do you have a targetSDK of 26 for the entire app with forced 26.0.1 support libs?