Scroll to view

[xarvic]

This PR adds the scroll_to_view and scroll_area_to_view methods to UpdateCtx, LifecycleCtx and EventCtx, which can be used to bring specific parts of a widget into view.

There are still some things to discuss:

• Currently the methods send commands if they are called from UpdateCtx or LifecycleCtx, but i am not sure this is the right way to do it.
• Calling the methods produces warnings, since the Notifications are passed up to the root. Should we hard code that this is intended behavior for this Selector or search for a better way to do it, like a supress_warnings flag in Notification?

[maan2003]

Some minor nits for now. haven't carefully reviewed default_scroll_to_view_handling logic yet. hope to get that done tomorrow

[xarvic]

On Desktop this should be fine, but it probably will cause problems on mobile. For an example focusing a textbox, will first update the scroll positions and then request the virtual-keyboard, which results in a layout change and therefore the text box is might be hidden again.
Do you have an idea how to solve this or is this a problem we should not care about for now?

[maan2003]

I think the fundamental problem is "the focused should stay in view" or "the focused widget should come in view once". maybe Scroll widget keeps track of a "focused" rect that will stay in view unless manually scroll away

[maan2003]

for this PR, I would just add scroll_to_view and not do it automatically on focus change yet

[xarvic]

Ok

[xarvic]

I think the fundamental problem is "the focused should stay in view" or "the focused widget should come in view once". maybe Scroll widget keeps track of a "focused" rect that will stay in view unless manually scroll away

A focused region that stays in in view until scrolled away sounds good, but i think keeping the rect wont be enough. If we have a two Scrolls in a Flex which again is wrapped in a Scroll, it could be possible that both of the inner Scrolls believe they contain the focused region and send Notifications to the outer Scroll.

[maan2003]

Thanks! Looks good