The previous code did not handle refreshing correctly; it retained some
of the cache, and tried merge new statuses in to the cache. This does
not work, and resulted in the app creating gaps in the timeline if more
than a page's worth of statuses had appeared since the user last
refreshed (e.g., overnight).
Fix this by treating the on-device cache as disposable, as the Paging3
library intends. On refresh the cached timeline is emptied and replaced
with a fresh page.
This causes a problem for state that is not stored on the server but is
part of a status' viewdata (has the user toggled viewing a piece of
media, expanded a CW, etc).
The previous code tried to work around that by pulling the state out of
the page cache and copying it in to the new statuses. That won't work
when the page cache is being destroyed.
So do it properly -- store the viewdata state in a separate (sparse)
table that contains only rows for statuses that have a non-default
state.
Save changes to the state when the user interacts with a status, and
use the state to ensure that the viewdata for a status in a thread
matches the viewdata for the same status if it is shown on the home
timeline (and vice-versa).
Fixes#16
402bcef588