topic Re: Persisting GS::Array<API_Neig> between SelectionChangeHandlerProc and ProjectEventHandlerP in Archicad C++ API

Persisting GS::Array between SelectionChangeHandlerProc and ProjectEventHandlerProc

kuvbur — Sat, 07 Feb 2026 18:25:53 GMT

How to persist GS::Array<API_Neig> between SelectionChangeHandlerProc and ProjectEventHandlerProc in ArchiCAD add-on? I want to save selection when switching windows (floor plans/sections). In SelectionChangeHandlerProc I capture selection with ACAPI_Selection_Get() into GS::Array<API_Neig>, then in ProjectEventHandlerProc catch APINotify_ChangeWindow/ChangeFloor/ChangeProjectDB and restore with ACAPI_Element_Select(). Problem: can't reliably pass array between callbacks. Tried global variables, static locals, singleton — all fail between invocations. What's the standard way to share data between ArchiCAD notifier callbacks?

Re: Persisting GS::Array between SelectionChangeHandlerProc and ProjectEventHandlerP

Ralph Wessel — Wed, 11 Feb 2026 10:21:24 GMT

I suggest taking a look at the API call ACAPI_KeepInMemory. Add-ons are unloaded from memory when not in use by default, which means they lose all variable data between one call and the next. But if you call ACAPI_KeepInMemory(true) you ask Archicad to persist the add-on in memory for the entire session, which means variable contents also persists between calls

Re: Persisting GS::Array between SelectionChangeHandlerProc and ProjectEventHandlerP

kuvbur — Tue, 17 Feb 2026 08:32:39 GMT

Thank you for your suggestion regarding ACAPI_KeepInMemory(true). I tried implementing it, but the data only persists within one Database. As soon as I switch to another window (e.g., from floor plan to section), the data in the array gets cleared.

~~Could you please advise on the correct approach?~~

I found a bug in my code — everything works perfectly now! Thank you so much for the helpful suggestion!