private void simpleButton1_Click(object sender, EventArgs e) { OpenFileDialog dialog = new OpenFileDialog(); dialog.Filter = "All Excel|*.xls;*.xlsx"; if (dialog.ShowDialog() == DialogResult.OK) { tFileName.EditValue = dialog.FileName; IEx = new ImportExcel(dialog.FileName); List <string> sheets = IEx.GetSheets(); lSheet.Properties.Items.Clear(); lSheet.Properties.Items.AddRange(sheets.ToArray()); } }