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function FindWindowByTitle(WindowTitle: string): Hwnd;
var
  NextHandle: Hwnd;
  NextTitle: array[0..260] of char;
begin
  // Get the first window
  NextHandle := GetWindow(Application.Handle, GW_HWNDFIRST);
  while NextHandle > 0 do
  begin
    // retrieve its text
    GetWindowText(NextHandle, NextTitle, 255);
    if Pos(WindowTitle, StrPas(NextTitle)) <> 0 then
    begin
      Result := NextHandle;
      Exit; 
    end
    else 
      // Get the next window 
      NextHandle := GetWindow(NextHandle, GW_HWNDNEXT);
  end; 
  Result := 0; 
end;
function FindControlByNumber(hApp: HWND; ControlClassName: string; EditNr: Integer): HWND; 
var 
  i: Word;
  hEdit: HWND;
begin
  Result := 0;
  if not IsWindow(hApp) then Exit;
  for i := 0 to EditNr do
  begin
    hEdit := FindWindowEx(hApp, hEdit, PChar(ControlClassName), nil);
    if hEdit = 0 then Exit;
  end;
  Result := hEdit;
end;


procedure TForm1.Button1Click(Sender: TObject);
var
  hEdit,h: hwnd;
begin
  hEdit := FindWindowByTitle('test');
  if hEdit = 0 then
    h := FindControlByNumber(FindWindow('test', nil), 'Richedit', 0);
  if h <> 0 then
      SendMessage(h, WM_SETTEXT, 0, Integer(PChar('test')))
  else
    ShowMessage('not found.');
end;