We are afraid that RadNavigation control does not support to customize items opening direction. The possible solution is to collapse all items when there is not enough space for sub-items. To achieve such behavior, you can set the minWidth
property. This determine a break-point where all items will be collapsed:
nav = $find(
Other possible solution is to use RadMenu
control, which has boundary detection integrated, so opening direction is calculated depending on space needed for displaying entire popup.