TOpenDialog, TSaveDialog,MessageDlg

procedure TForm1.FileOpenClick(Sender: TObject);
var
  getStream: TFileStream;
begin
  if isOpen then
    if openDialog1.Execute then
      FFileName := openDialog1.FileName;
  Encoding := Form22.GetTextEncoding(FFileName);
  getStream := TFileStream.Create(FFileName, fmOpenRead or fmShareDenyNone);
  richEdit.Lines.LoadFromStream(getStream, Encoding);
  getStream.Free;
  Form1.Caption := FFileName;
  isOpen := true;
end;

procedure TForm1.FileSaveAsClick(Sender: TObject);
var
  SetStream: TFileStream;
  temp: TStringList;
begin
  if SaveDialog1.Execute then
  begin
    if FileExists(SaveDialog1.FileName) then
      if MessageDlg('是否保存到' + SaveDialog1.FileName,
        mtConfirmation, [mbYes, mbNo], 0) <> mrYes then Exit;
    SaveFile(SaveDialog1.FileName);
    richEdit.Modified := False;
  end;
end;

function TForm1.SaveFile(const FileName: string): boolean;
var
  SetStream: TFileStream;
  temp: TStringList;
begin
  SetStream := TFileStream.Create(FileName, fmCreate);
  temp := TStringList.Create;
  temp.AddStrings(richEdit.Lines);
  temp.SaveToStream(SetStream, Encoding);
  temp.Free;
  SetStream.Free;
end;