private void chck_all_prd()
            {

            for (int i = 0; i < DataGrid1.Items.Count; i++)
                {
                var row1 = (DataGridRow)DataGrid1.ItemContainerGenerator.ContainerFromIndex(i);

                if (row1 == null) continue;
                var chk = (System.Windows.Controls.CheckBox)DataGrid1.Columns[0].GetCellContent(row1);
                chk.IsChecked = true;

                }
            }

        private void chbxAll_Unchecked(object sender, RoutedEventArgs e)
            {
            for (int i = 0; i < DataGrid1.Items.Count; i++)
                {
                var row1 = (DataGridRow)DataGrid1.ItemContainerGenerator.ContainerFromIndex(i);

                if (row1 == null) continue;
                var chk = (System.Windows.Controls.CheckBox)DataGrid1.Columns[0].GetCellContent(row1);
                chk.IsChecked = false;

                }
            }