subroutine CancelSub( dlg, id, callbacktype )
  use ProgressBox
  use user32
  implicit none
  ! Arguments
  type (dialog) dlg
  integer id, callbacktype
  ! Variables
  type(PBContext) context
  pointer ( pc, context )
  integer iret
  ! Set the bCancelled flag in the context block.  
  ! SetProgress checks this flag and returns PBStatus_Aborted
  if (callbacktype == dlg_clicked) then
    !  Get the "context" window property
    pc = GetProp( dlg % hwnd, "PBContext" )
    context % bCancelled = .TRUE.
  endif
end subroutine CancelSub