DBGrid保存EXCEL

function TForm1.ExportDBGrid(DBGrid: TDBGrid; SheetName: string): Boolean;   //直接保存，不显示EXCEL
var
c, r, i, j: integer;
app: Olevariant;
TempFileName, ResultFileName: string;
begin
try
    result := True;
      app := CreateOLEObject('Excel.application');
    // app.WorkBooks.Add(xlWBatWorkSheet);
    except
      Application.MessageBox('Excel没有正确安装！','警告',MB_OK);
      result := False;
      exit;
    end;
    SaveDialog1.DefaultExt := 'xls';
    SaveDialog1.FileName := SheetName;
    if SaveDialog1.Execute then
      TempFileName := SaveDialog1.FileName
    else
      Exit;
    app.Workbooks.add;
    app.Visible := false;
    Screen.Cursor := crHourGlass;
    DBGrid.DataSource.DataSet.First;
    c := DBGrid.DataSource.DataSet.FieldCount;
    r := DBGrid.DataSource.DataSet.RecordCount;
    Application.ProcessMessages;
    for i := 0 to c - 1 do
      app.cells(1, 1 + i) := DBGrid.DataSource.DataSet.Fields[i].DisplayLabel;
    for j := 1 to r do
    begin
      for i := 0 to c - 1 do
        app.cells(j + 1, 1 + i) := DBGrid.DataSource.DataSet.Fields[i].AsString;
      DBGrid.DataSource.DataSet.Next;
    end;
    ResultFileName := TempFileName;
    if ResultFileName = '' then
      ResultFileName := '数据导出';
    if FileExists(TempFileName) then
     DeleteFile(TempFileName);
    app.Activeworkbook.saveas(TempFileName);
    app.Activeworkbook.close(false);
    app.quit;
    app := unassigned;
end;