Show placeholder if there are no messages in folder

[marbetschar]

Problem

Right now there is no placeholder image or indication that a folder contains no messages:

Proposal

We should display some sort of placeholder, so the user does not think this is due to an error. In case we are dealing with the inbox folder it would be even nicer to show some rewarding thing which celebrates the fact that there is "nothing to do".

Prior Art

Seen this "Yay, you're all done :partying_face:" in quite a lot of different places. Despite, I'm still a little proud of myself every time I get to see this :) Here's just one example of what GitHub does:

[cassidyjames]

@marbetschar I'm in favor of an AlertView here or something, but I want to double-check, is this sometimes blank when there are just no mails fetched, but we're expecting to show some? It would be awkward on first set-up to have something cheeky like

:tada: Inbox Zero! There are no messages here. You’ve achieved inbox zen.

…just to throw a bunch of mails in their face in a second :sweat_smile:

[cassidyjames]

To be less cheeky, we could do an AlertView as simple as:

:heavy_check_mark: No Messages If you’re expecting something, try fetching new messages.

[marbetschar]

Sounds good to me 👍

[casasfernando]

Also when the last message in the folder is deleted, this placeholder should be displayed as well, instead of keeping the last selected message content in the view pane.

Wasn't sure if I should report this here or as a new issue so just let me know if you want me to go with the second option.

Thanks.

[danirabbit]

@casasfernando that sounds like a separate issue. Could you indeed open another report for that? :)

[casasfernando]

Sure @danrabbit, will do.

Thanks.