If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  ComboBoxGadget(1,10,10,100,20,0)
  ButtonGadget(2,120,10,100,20,"Anzeigen",0)
  
  AddGadgetItem(1,-1,"Teststring",0,0)
Repeat
EventID=WaitWindowEvent()
If EventID=#PB_Event_Gadget
  Select EventGadget()
   Case 2
     SendMessage_(GadgetID(1),#CB_SHOWDROPDOWN,1,1)
  EndSelect
EndIf
Until EventID = #PB_Event_CloseWindow
EndIf