uses shlobj;


function TfrmMain.OpenFolder(root: Integer; Caption: string): string; //Verzeichnis-Öffnen-Dialog-Funktion
var
  bi: TBrowseInfo;
  lpBuffer: PChar;
  pidlPrograms, pidlBrowse: PItemIDList;
begin
  if (not SUCCEEDED(SHGetSpecialFolderLocation(GetActiveWindow, root,
    pidlPrograms))) then
    exit;
  lpBuffer := StrAlloc(MAX_PATH);
  bi.hwndOwner := GetActiveWindow;
  bi.pidlRoot := pidlPrograms;
  bi.pszDisplayName := lpBuffer;
  bi.lpszTitle := PChar(Caption);
  bi.ulFlags := BIF_RETURNONLYFSDIRS;
  bi.lpfn := nil;
  bi.lParam := 0;

  pidlBrowse := SHBrowseForFolder(bi);
  if (pidlBrowse <> nil) then
    if SHGetPathFromIDList(pidlBrowse, lpBuffer) then
      Result := lpBuffer;
  StrDispose(lpBuffer);
end;

procedure TfrmMain.cmdOpenClick(Sender: TObject);
begin
  txtPath.Caption := OpenFolder(CSIDL_DRIVES, 'Verzeichnis wählen'); //Übergabe des gewählten Verzeichnisses
end;