When viewing a media in the media preview, you can delete it by pressing
a delete button on the action bar. It will then ask you to confirm your
choice. If you confirm, it will delete the attachment from the database
and from disk. If it was the only attachment for that message, the
message itself will also be deleted.
1) Migrate from GSON to Jackson everywhere.
2) Add support for storing identity key conflicts on message rows.
3) Add limited support for surfacing identity key conflicts in UI.
1) Allow imports from the stock SMS database at any time.
2) Provide plaintext export support, in a format compatible with
the "SMS Backup And Restore" app.
3) Fix the DB weirdness on encrypted restore that previously
required killing the app.
