Caret in ComboBox

[DBR]

Delphi-Quellcode:

const
  Hook: Hhook = 0;

var
  pos: integer;

procedure TForm1.ComboBox1KeyUp(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  pos := Combobox1.selstart;
end;

function MouseProc(HookCode: Integer; WParam: WPARAM;
  LParam: LPARAM): LRESULT; stdcall;
var pt: TPoint;
begin
  if (HookCode = HC_ACTION) and (WParam = WM_LBUTTONUP) then begin
    with Form1.Combobox1 do begin
      pt := ScreenToClient(PMOUSEHOOKSTRUCT(LParam)^.pt);
      if ptinrect(rect(0, 0, width, height), pt) then begin
        pos := selstart;
        result := 0;
        exit;
      end;
    end;
  end;
  result := CallNextHookEx(Hook, HookCode, WParam, LParam);
end;

procedure HookInst;
begin
  if Hook <> 0 then exit;
  Hook := SetWindowsHookEx(WH_MOUSE, MouseProc,
    HInstance, GetCurrentThreadId);
  if Hook = 0 then
    MessageBox(0, 'Der Hook wurde nicht installiert!',
      'FEHLER', MB_ICONERROR);
end;

procedure HookUninst;
begin
  if Hook <> 0 then UnhookWindowsHookEx(Hook);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
// ---- zum Testen ---------------
  combobox1.items[0] := 'Zeile 1';
  combobox1.items[1] := 'Zeile 2';
  combobox1.items[2] := 'Zeile 3';
  combobox1.items[3] := 'Zeile 4';
  combobox1.items[4] := 'Zeile 5';
// ------------------------------
  combobox1.itemindex := 0;
  HookInst;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  HookUninst;
end;

procedure TForm1.Button1Click(Sender: TObject);
var s: string;
begin
  s := Combobox1.text;
  insert('###', s, pos);
  Combobox1.text := s;
end;

Gruß DBR