Can't invoke double click on datagrid

[Shirley]

hi,
   SL5 support double click by the "ClickCount".But on the RadGridView, it won't invoke the event "MouseLeftButtonUp" when i click the data row.But when i click on the blank area it invoke, but the ClickCount always is 1.
Is any body know what's the matter?

My code like below:

<telerik:RadGridView  AutoGenerateColumns="False" ShowGroupPanel="False" x:Name="dg" Grid.Row="0" Grid.Column="0" ScrollMode="RealTime"  DataLoadMode="Synchronous"
                              Width="auto"  ShowGroupFooters="True" IsReadOnly="True"  MouseLeftButtonUp="dg_MouseLeftButtonUp"
                                            EnableRowVirtualization="True" RowIndicatorVisibility="Collapsed"   EditTriggers="CellClick" >
            <telerik:RadGridView.Columns>

                <telerik:GridViewDataColumn Header="ID" Width="120" DataMemberBinding="{Binding C_id,Mode=TwoWay}">

</telerik:RadGridView.Columns>
</telerik:RadGridView>

 void dg_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            //双击选中
            if (e.ClickCount == 2)
            {
               //do something
            }
        }

Thanks for your help.
Shirley