public string LeggiValore(string foglio, int indicecolonna, int indiceriga)
{
 Excel.Application ObjFileExcel = new Excel.Application();
 Excel.Workbook XlwbDati;
 Excel.Worksheet XlshDati;
 object oMissing = System.Reflection.Missing.Value;
 try {
   LeggiValore = "";
   XlwbDati = ObjFileExcel.Workbooks.Open(this.percorsofile, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing, oMissing);
   XlshDati = XlwbDati.Sheets.Item(foglio);
   LeggiValore = XlshDati.Cells(indiceriga, indicecolonna).value + "";
   ObjFileExcel.Quit();
   System.Runtime.InteropServices.Marshal.ReleaseComObject(ObjFileExcel);
 } catch (Exception ex) {
   ObjFileExcel = null;
   XlwbDati = null;
 }
}