EnableExplicit

Define a

If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  ComboBoxGadget(1,10,10,100,20,0)
  For a=1 To 5
    AddGadgetItem(1,-1,"TestItem",0,0)
  Next
  
  MessageRequester("","Anzahl der Items: "+Str(SendMessage_(GadgetID(1),#CB_GETCOUNT,0,0)),0)
Repeat : Until WaitWindowEvent() = #PB_Event_CloseWindow
EndIf