Sorting and Scrolling problem in wpf datagrid

I was facing this issue because of drag and drop datagrid items
I added following code in PreviewMouseLeftButtonDown and Drop events of datagrid

DataGrid grd = e.Source as DataGrid;
if (grd == null)
return;

//make sure the row under the grid is being selected
Point position = e.GetPosition(grd);
var row = UIHelpers.TryFindFromPoint(grd, position);
if (row == null) return;