By default, DataGrid will not sort the underlying collection when displayed in the grid. When you sort a column, internally datagrid will maintain the underlying collection and does a sort that reflects only in view. So, if you want to sort the underlying collection of view model, you can apply sorting by using SortColumnChanged event.
Note: In Silverlight, the following code sample can be used to get the current sort column value.
Here, the underlying collection of SfDataGrid is taken by GetValue. If sortColumn.Direction is ListSortDirection.Ascending the sorting is applied for that collection in ascending direction, that is based on SortDescriptions column, otherwise it will be sorted in descending direction. OrderSource method is used to get the column value.
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