osx - When it's a right time to -expandItem: in a NSOutlineView? -

i have nsoutlineview use display items grouped sections.

┌──────────────────────────────┐ │ section 0                    │ └──────────────────────────────┘   ┌────────────────────────────┐   │ item 0                     │   └────────────────────────────┘   ┌────────────────────────────┐   │ item 1                     │   └────────────────────────────┘ ┌──────────────────────────────┐ │ section 1                    │ └──────────────────────────────┘   ┌────────────────────────────┐   │ item 2                     │   └────────────────────────────┘ 

outline view backed custom fetched results controller issues 2 kinds of notifications on model changes:

• insert/move/delete section @ index (to index)
  when notification insert/move/delete item @ root level of outline view.
• insert/update/move/delete item @ index in section (to index in section)
  when notification insert/update/move/delete item @ corresponding section level.

that is, manage outline view in incremental fashion , didn't make single -reloaddata call.

everything works expected. the sole problem need sections appear expanded.

unfortunately, nsoutlineview api doesn't allow insert item in expanded state beginning. , there no obvious way customize behaviour via subclassing (i used hopper disassembler learn nsoutlineview internals, correct me if wrong).

my first attempt call -expanditem: after insert section, doesn't have effect @ all.

the second attempt call -expanditem: before add first nested item simulated section. has side effect of double insert.

the workaround found delay -expanditem: call this:

id section = ...  dispatch_async(dispatch_get_main_queue(), ^ {   [self.outlineview expanditem: section]; }); 

this feels ugly , doesn't solve problem completely. example, more 1 section being added in 1 batch. item moves existing section new one, created , want row movement animation happen. instead corrupted nsoutlineview layout, section row gets clipped after section populated first time via -insertitemsatindexes:inparent:withanimation:. run loop trick ruins everything.

so question is, when right time expand item, inserted via -insertitemsatindexes:inparent:withanimation:?