Element-android: Read markers

[nadonomy]

(Internal) zeplin: https://zpl.io/VkeZXQg

Unread messages

• [ ] Show unread messages banner when there are unread messages
• [ ] Tap anywhere to action banner, tap [x] to dismiss, also updating read marker
• [ ] Automatically hide banner after 10s of inactivity

Scroll down / new messages

• [ ] Show new messages floating button after scrolling up (shouldn't appear while actively scrolling)
• [ ] Show new messages badge on floating button if they appear while scrolled up

@bwindels or @ara4n we spoke in some detail about the read marker UX in Riot Web last year, with notes captured here: https://docs.google.com/document/d/1PAZYgCfrGJuDOYGTJ8HZH7Pd2LK0yUkW13C9FMwhWHw/edit#

Could either of you speak to the implementation we arrived at in the end?

[bwindels]

Yes, riot web does the following with the read markers (mostly unrelated to read receipts) currently:

• if the read marker is above the viewport, we show an arrow up with a green badge with a dot in it to scroll up to the read marker. The read marker is set after the last visible message after 30s of user activity*.

• if the read marker is in the viewport, no button is shown, and the read marker is put after the last visible message after 1s of user activity*.

• if the read marker is below the viewport, we don't change it automatically. If new messages arrive, we show a badge on the arrow button to scroll down, but I don't think this is based on the position of read marker, it is just something we reset when you scroll to the bottom.

• ask me what user activity means in riot web if your curious.

[bwindels]

Also see https://github.com/matrix-org/matrix-react-sdk/pull/2345#issue-237724855

[bmarty]

Handle in #592