Silverlight Datagrid Combobox SelectedIndex Binding

See more:

C#

ASP.NET

WCF

Silverlight

Hi,

In my silverlight application, I have a combobox in my datagrid that binds to a class.
When I change the combobox, I can get the Index to the class, But the combobox doesn't change when I update the class programmatically
Please Help me to sort this out. urgent.

<data:datagridtemplatecolumn header="Sale Unit" width="80" xmlns:data="#unknown">
    <data:datagridtemplatecolumn.celleditingtemplate>
        <datatemplate>
            <combobox itemspanel="{Binding RelativeSource={RelativeSource Self}}" datacontext="{Binding}" selectedindex="{Binding Path=cursunit,Mode=TwoWay}" keydown="ComboBox_KeyDown" loaded="ComboBox_Loaded" selectionchanged="ComboBox_SelectionChanged">
                <comboboxitem content="BOX" />
                <comboboxitem content="STRIP" />
                <comboboxitem content="PEICE" />
            </combobox>
        </datatemplate>
    </data:datagridtemplatecolumn.celleditingtemplate>
</data:datagridtemplatecolumn>