Procedure DisplayMenuInGadget(Window.l, Gadget.l, Menu.l)
  Protected Rect.rect, Pt.point
  GetClientRect_(GadgetID(Gadget), @Rect)
  Pt\x = Rect\left - 1
  Pt\y = Rect\bottom
  ClientToScreen_(GadgetID(Gadget), @Pt)
  DisplayPopupMenu(Menu, WindowID(Window), Pt\x, Pt\y)
EndProcedure

If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  ButtonGadget(1,10,10,100,20,"Menü öffnen",0)
  
  If CreatePopupMenu(1)
    For a=1 To 5
      MenuItem(a,"Testitem "+Str(a))
    Next
  EndIf
  
Repeat
EventID=WaitWindowEvent()
If EventID=#PB_Event_Gadget
  Select EventGadget()
    Case 1
      DisplayMenuInGadget(0,1,1)
  EndSelect
EndIf
If EventID=#PB_Event_CloseWindow
  Quit=1
EndIf
Until Quit=1
EndIf