objective c - ReloadData with expanded items not refreshing children -

i have simple nsoutlineview works nice far. thing did not work when issue reloaddata(). have expanded item , reason reload 1 child added new child not appear. parent refreshed see number of children (which output too) updated. new child not appear.

i circumvented behavior collapsing parent when adding or deleting child items. wonder if there trick children refreshed maintaining expansion state of parent is.

could use reloaditem:reloadchildren: on nsoutlineview when want reload? if want refresh reload root item passing 'nil' first parameter.