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scrollbox1.VertScrollBar.Position := GetScrollPos(RichEdit1.Handle, SB_VERT);					

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scrollbox1.VertScrollBar.visible := False;					

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procedure TForm1.RichEdWndProc(var Msg: TMessage);
begin
  Msg.Result := CallWindowProc(POldWndProc, RichEdit1.Handle, Msg.Msg, Msg.WParam,
    Msg.LParam);

  if (Msg.Msg = WM_VSCROLL)  then
  begin
    Label1.Caption := 'scrollbar move' + IntToStr(HIWORD(Msg.Wparam));
    RichEdit1.SelStart := RichEdit1.Perform(EM_LINEINDEX,
      RichEdit1.Perform(EM_GETFIRSTVISIBLELINE, 0, 0), 0) + 1;
  end;
end;					

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if (Msg.Msg = WM_Pfeil_Down ???? ) then  ...					

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unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ComCtrls;

type
  TRichEdit=Class(ComCtrls.TRichEdit)

  private
    procedure WndProc(var Msg: TMessage);override;
  End;
  TForm1 = class(TForm)
    RichEdit1: TRichEdit;
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
procedure TRichEdit.WndProc(var Msg: TMessage);
begin

  if (Msg.Msg =  WM_VSCROLL)
  or ((Msg.Msg = WM_KeyDown) and (Msg.WParam in [VK_Down,VK_UP]))
  or (msg.Msg =  WM_MouseWheel)
  then
  begin
     msg.Result := 0;
  end
  else inherited;
end;

end.