childFocusNode property
final
The childFocusNode attribute is the optional FocusNode also associated the child or builder widget that opens the menu.
The focus node should be attached to the widget that should receive focus if keyboard focus traversal moves the focus off of the submenu with the arrow keys.
If not supplied, then keyboard traversal from the menu back to the controlling button when the menu is open is disabled.
Implementation
final FocusNode? childFocusNode;