How to Change the Sorting in code behind 2016 r3 silverlight

[M]

I want change or set a new sorting in telerik reporting 2016 r3 in code behind.I am using silverlight.

I cannot to update or set the new sorting. It does not work?

I tried to use below code in need_datasource (before or after datasource assignning) but does not effect.

Telerik.Reporting.Sorting sorting1 = new Telerik.Reporting.Sorting();

sorting1.Expression = "=Fields.MyField";

sorting1.Direction = Telerik.Reporting.SortDirection.Asc;

this.report.Sortings.Add(sorting1);

 or by direct assigning :

this.report.Sortings.Add(new instance with new expression and direction);

Does not work!