Fix append positioning behavior for collections with `renderFromLast=true`

[pzuraq]

Currently, collections will never fix their scroll position when items are appended. When collections use renderFromLast=true and they are scrolled all the way to the bottom, appended items should push scroll top down more. This is the expected behavior for messaging apps and other users of this setting.

[makepanic]

I think we're affected by this issue. Is there any chance on fixing this bug?

If not, could you maybe point in a direction where the scroll correction is happening for the other cases?

thanks

[pzuraq]

@runspired and I ended up discussing for a while the best way to fix this issue. We want to add a few different APIs that would allow users to modify the scroll position either imperatively or by specifying behavior for these situations (like on prepend and on append), and neither of us has really had the time to dig in to figure those out. Hopefully sometime after EmberConf

[NullVoxPopuli]

is the scrolling for this totally controlled by js? or can we use the default / css way of auto-scrolling to the end?

I have a messaging app, and recently just added vertical-collection, and I lost the auto-scroll-to-end ness that my css was providing :-\

[pzuraq]

Scrolling is actually completely not controlled by JS, VC just reacts to user scroll. That said, if you have dynamic height items I could see it interfering, or if you’re adding items dynamically.

[josiahbryan]

Any luck on this? I'm working on the exact same thing - messaging app and needing to scroll to bottom.