[list-box] Reset the focused item when connected (or disconnected) from the DOM

[jouni]

When the list box is connected to the DOM, we should reset the focused item either to the first selected item or, if there is no selected item, to the first item in the list.

This would at least help when used inside vaadin-context-menu, where the common case is that when the menu opens the focus should be on the first item in the menu.

[platosha]

Note that resetting focus on when connected might break overlays with list box inside, e. g., the dropdown menu.

Removing focus indication when disconnected should be fine, since naturally disconnected elements loose focus anyway.

[jouni]

Why would it break?

I’m not talking about removing focus indication, though. I’m talking about changing which item has the focus indication and keyboard focus when the list-box becomes visible.

Maybe we should even switch the focus back to the first (selected) item when the list-box itself loses focus? Is there a benefit of letting the user return to the previous item they had keyboard focus on? It’s not visible at least, so it can be a bit arbitrary for the user where the keyboard focus lands in a longer list. Could be more expected that it always lands on the first (selected) item.