Silverlight Combobox Selection changed event problem

Hi,

I am getting the ComboBoxIndex from DataGrid Hyperlink Button.

if(i !=null)
{
cbgrpsList.SelectedIndex = i; --> "i" is from the DataGrid Hyperlink Button.
cbgrpsList.SelectionChanged += new SelectionChangedEventHandler(cbgrpsList_SelectionChanged);
}
else
{
cbgrpsList.SelectedIndex = 0;
cbgrpsList.SelectionChanged += new SelectionChangedEventHandler(cbgrpsList_SelectionChanged);
}

This is how I wrote the code. If I am getting the Index from DataGrid Hyperlink I am using "if" condition otherwise I just selecting the index 0.

When I normally changing the selection from Combo Box the selection changed event is firing normally. But when I getting the selected index from Data Grid Hyperlink Button that Selection changed event is not firing.

How can I do this... Plz help

Regards,
Murali.