vb.net - Detect if progress bar value was assigned before P/INVOKE PBM_SETSTATE -

i'm making library progressbar includes p/invoke native methods progress state.

<toolboxbitmap(gettype(progressbar))> public class myprogressbar : inherits progressbar      private const pbm_setstate integer = &h400 + 16      private _state progressstates = progressstates.normal      <dllimport("user32.dll", charset:=charset.auto, setlasterror:=false)>     private shared function sendmessage(byval hwnd intptr, byval msg integer, byval wparam intptr, byval lparam string) intptr     end function      public sub new()         mybase.new()     end sub      <category("appearance")>     <defaultvalue(progressstates.normal)>     <description("it sets progress state")>     public property state progressstates                     return _state         end         set(value progressstates)             _state = value             me.recreatehandle()         end set     end property      public enum progressstates         normal = &h1         [error] = &h2         paused = &h3     end enum      protected overrides sub oncreatecontrol()         mybase.oncreatecontrol()         sendmessage(me.handle, pbm_setstate, _state, intptr.zero)     end sub  end class 

i have problem:
when pbm_setstate called before value assigned, progressbar value 0.

is there way detect if value assigned progress bar before call pbm_setstate p/invoke?
want this: when value assigned, automatically call pbm_setstate.

you cannot set state of progressbar before assigning value
must assign value, @ least 1 time (before setting state).

i suppose .net framework sends pbm_setpos when value property changed.

the short question is:
how tell if pbm_setpos called? pbm_setstate not work until pbm_setpos called.

did try send pbm_getpos , check if it's null?

if sendmessage(progressbar.handle, pbm_getpos, 0, 0) isnot nothing     'do stuff here end if