怎样在TMemo控件中用TFindDialog实现查找文本，用TReplaceDialog实现替换文本功能？

Question

//查找
procedure TForm1.FindClick(Sender:TObject)
var
  where:integer;
begin
  if FindDialog1.Execute then
  begin
    where:=Pos(FindDialog1.FindText,Memo1.Lines.Text);
    if where=0 then
      ShowMessage('找不到')
    else begin
      Memo1.SelStart:=where-1;
      Memo1.SelLength:=Length(FindDialog1.FindText);
    end;
  end;
end;//替换
procedure TForm1.ReplaceClick(Sender:TObject);
var
  where:integer;
begin
  if ReplaceDialog1.Execute then
  begin
    where:=Pos(ReplaceDialog1.FindText,Memo1.Lines.Text);
    if where=0 then
      ShowMessage('找不到'+ReplaceDialog1.FindText);
    else beign
      Memo1.SelStart:=where-1;
      Memo1.SelLength:=Length(ReplaceDialog1.FindText);
      Memo1.SelText:=ReplaceDialog1.ReplaceText;
    end;
  end;
end;