public void Acquire(short ShowUI, short ModalUI)
        {
            TwRC rc;

            CloseSrc();
            if (appid.Id == IntPtr.Zero)
            {
                Init(hwnd);
                if (appid.Id == IntPtr.Zero)
                {
                    return;
                }
            }
            rc = DSMident(appid, IntPtr.Zero, TwDG.Control, TwDAT.Identity, TwMSG.OpenDS, srcds);
            if (rc != TwRC.Success)
            {
                return;
            }

            TwCapability cap = new TwCapability(TwCap.XferCount, -1);

            rc = DScap(appid, srcds, TwDG.Control, TwDAT.Capability, TwMSG.Set, cap);
            if (rc != TwRC.Success)
            {
                CloseSrc();
                return;
            }


            TwUserInterface guif = new TwUserInterface();

            guif.ShowUI     = ShowUI;
            guif.ModalUI    = ModalUI;
            guif.ParentHand = hwnd;



            rc = DSuserif(appid, srcds, TwDG.Control, TwDAT.UserInterface, TwMSG.EnableDS, guif);
            if (rc != TwRC.Success)
            {
                CloseSrc();
                return;
            }
        }
 private static extern TwRC DScap([In, Out] TwIdentity origin, [In] TwIdentity dest, TwDG dg, TwDAT dat, TwMSG msg, [In, Out] TwCapability capa);