ShowModal，要按两次才可以,该怎么处理

procedure tmainform.FormCreate(Sender: TObject);
var
  Login:TLoginForm;
begin
  Login :=TLoginForm.Create(Self);
  if Login.ShowModal=mrOk then
  begin

  end;
end;

procedure TLoginForm.Button2Click(Sender: TObject);//Button2的默认ModalResult为mrNone
begin
  if (Length(Trim(Edit1.Text))=0) then
  begin
    ShowMessage('输入帐号');
    Exit;
  end;
  if (Length(Trim(Edit2.Text))=0) then
  begin
    ShowMessage('输入密码');
    Exit;
  end;
  Button2.ModalResult :=mrOk;
end;