how to set current cell in wpf gatagrid

DataGridCell objCellToFocus = DataGridExtensions.GetCell(Dg,(DataGridRow)Dg.ItemContainerGenerator.ContainerFromIndex(1), 2);
            objCellToFocus.Focus();

public static class DataGridExtensions
    {
        public static DataGridCell GetCell(this DataGrid grid, DataGridRow row, int columnIndex = 0)
        {
            if (row == null) return null;

            var presenter = FindVisualChild<datagridcellspresenter>(row);
            if (presenter == null) return null;

            var cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(columnIndex);
            if (cell != null) return cell;

            // now try to bring into view and retreive the cell
            grid.ScrollIntoView(row, grid.Columns[columnIndex]);
            cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(columnIndex);

            return cell;
        }

        public static IEnumerable<t> FindVisualChildren<t>(DependencyObject depObj) where T : DependencyObject
        {
            if (depObj != null)
            {
                for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
                {
                    DependencyObject child = VisualTreeHelper.GetChild(depObj, i);
                    if (child != null && child is T)
                    {
                        yield return (T)child;
                    }

                    foreach (T childOfChild in FindVisualChildren<t>(child))
                    {
                        yield return childOfChild;
                    }
                }
            }
        }

        public static childItem FindVisualChild<childitem>(DependencyObject obj) where childItem : DependencyObject
        {
            foreach (childItem child in FindVisualChildren<childitem>(obj))
            {
                return child;
            }

            return null;
        }
    }
</childitem></childitem></t></t></t></datagridcellspresenter>