private void btn_esporta_excel_Click(object sender, EventArgs e)
        {

            Microsoft.Office.Interop.Excel.Application excelApp = null;
            try
            {
                // instantiating the excel application class
                excelApp = new Microsoft.Office.Interop.Excel.Application();
                Microsoft.Office.Interop.Excel.Workbook currentWorkbook = excelApp.Workbooks.Add(Type.Missing);
                Microsoft.Office.Interop.Excel.Worksheet currentWorksheet = (Microsoft.Office.Interop.Excel.Worksheet)currentWorkbook.ActiveSheet;
                currentWorksheet.Columns.ColumnWidth = 18;


                if (dataGridView_utenti.Rows.Count > 0)
                {
                    currentWorksheet.Cells[1, 1] = DateTime.Now.ToString("dd/MM/yyyy HH:mm");
                    int i = 1;
                    foreach (DataGridViewColumn dgviewColumn in dataGridView_utenti.Columns)
                    {
                        // Excel work sheet indexing starts with 1
                        currentWorksheet.Cells[2, i] = dgviewColumn.Name;
                        ++i;
                    }
                    Microsoft.Office.Interop.Excel.Range headerColumnRange = currentWorksheet.get_Range("A2", "M2");
                    headerColumnRange.Font.Bold = true;
                    headerColumnRange.Font.Color = 0xFF0000;

                    //imposto la colonna mansione (la più lunga) a 50
                    Microsoft.Office.Interop.Excel.Range mansione = currentWorksheet.get_Range("D2", "D2");
                    mansione.EntireColumn.ColumnWidth = 50;
                    //headerColumnRange.Rows
                    //headerColumnRange.Columns.AutoFit();
                    int rowIndex = 0;
                    for (rowIndex = 0; rowIndex < dataGridView_utenti.Rows.Count; rowIndex++)
                    {
                        DataGridViewRow dgRow = dataGridView_utenti.Rows[rowIndex];
                        for (int cellIndex = 0; cellIndex < dgRow.Cells.Count; cellIndex++)
                        {
                            currentWorksheet.Cells[rowIndex + 3, cellIndex + 1] = dgRow.Cells[cellIndex].Value;
                        }
                    }
                    Microsoft.Office.Interop.Excel.Range fullTextRange = currentWorksheet.get_Range("A1", "M" + (rowIndex + 1).ToString());
                    fullTextRange.WrapText = true;
                    //fullTextRange.HorizontalAlignment = Microsoft.Office.Interop.Excel.XlHAlign.xlHAlignLeft;
                }
                else
                {
                    string timeStamp = DateTime.Now.ToString("dd/MM/yyyy HH:mm");
                    currentWorksheet.Cells[1, 1] = timeStamp;
                }
                using (SaveFileDialog exportSaveFileDialog = new SaveFileDialog())
                {
                    exportSaveFileDialog.Title = "Seleziona il percorso";
                    exportSaveFileDialog.Filter = "Microsoft Office Excel Workbook(*.xlsx)|*.xlsx";

                    if (DialogResult.OK == exportSaveFileDialog.ShowDialog())
                    {
                        string fullFileName = exportSaveFileDialog.FileName;
                        // currentWorkbook.SaveCopyAs(fullFileName);
                        // indicating that we already saved the workbook, otherwise call to Quit() will pop up
                        // the save file dialogue box

                        currentWorkbook.SaveAs(fullFileName, Microsoft.Office.Interop.Excel.XlFileFormat.xlOpenXMLWorkbook, System.Reflection.Missing.Value, Missing.Value, false, false, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlNoChange, Microsoft.Office.Interop.Excel.XlSaveConflictResolution.xlUserResolution, true, Missing.Value, Missing.Value, Missing.Value);
                        currentWorkbook.Saved = true;
                        MessageBox.Show("File salvato con successo", "Esportato su file Excel", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Exception", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            finally
            {
                if (excelApp != null)
                {
                    excelApp.Quit();
                }
            }

        }