Save the sortorder from a datagrid

Question

I whant to save the sortorder and the selectedIndex from my Silverlight datagrid.

I use:

Application.Current.Resources.Add("CurrentIndex", dg.SelectedIndex);

to save the selectedIndex.

If my list was sorted when i selected a item the index will not be correct when returning to the datagrid. How do I save the sortorder so the correct item will be highlighted?