begin edit cell in datagrid without double click mouse to edit

my code in Grid_PreviewKeyDown event:

var uie = e.OriginalSource as UIElement;

            if (e.Key == Key.Enter)
            {
                e.Handled = true;
                uie.MoveFocus(
                new TraversalRequest(
                FocusNavigationDirection.Next));
            }

then the cell is selected but not move a cursor and open to edit .. without double click mouse on cell. why??