stop dialog form from closing

procedure TForm1.button1Click(Sender: TObject);
  var
  f:TAddRes;
begin
    f := TAddRes.Create(Self);
  try
    f.ShowModal;
  finally
    f.Release;
  end;
end;

//dialog form below
//the modalresult on the dialog form is set to mrOK 

procedure TForm2.OKbuttonClick(Sender: TObject);
begin
     if (TitleEdit.Text = '') or (FirstNEdit.Text = '') or (LastNEdit.Text ='') 
or (PostEdit.Text = '') or (AddrMemo.Text = '')
     then begin
     ShowMessage('Please Complete All Required Fields');

     end
     else
     begin
//do something
  end;
end;

if not SomeCondition then
begin
  ShowMessage('You have not entered something');
  Abort;
end;