I am using a DataGrid in my silverlight project which contains a custom checkbox column. I have binded its command property with a property of my ViewModel class. Now, the problem is that I want to send the "selected item" of DataGrid through the command paramter for which I have written the following code :

<sdk:DataGrid AutoGenerateColumns="False" Margin="10,0,10,0" Name="dataGridOrders" ItemsSource="{Binding OrderList}" Height="190">
                    <sdk:DataGrid.Columns>
                        <sdk:DataGridTemplateColumn Header="Select">
                            <sdk:DataGridTemplateColumn.CellTemplate>
                                <DataTemplate>
                                    <CheckBox>
                                        <is:Interaction.Triggers>
                                        <is:EventTrigger EventName="Checked">
                                                <is:InvokeCommandAction Command="{Binding Source={StaticResource ExecutionTraderHomePageVM},Path=OrderSelectedCommand,Mode=TwoWay}"
                                                                        CommandParameter="{Binding ElementName=dataGridOrders,Path=SelectedItem}" />
                                        </is:EventTrigger>
                                            <is:EventTrigger EventName="Unchecked">
                                                <is:InvokeCommandAction Command="{Binding Source={StaticResource ExecutionTraderHomePageVM},Path=OrderSelectedCommand,Mode=TwoWay}"
                                                                        CommandParameter="{Binding ElementName=dataGridOrders,Path=SelectedItem}" />
                                            </is:EventTrigger>
                                        </is:Interaction.Triggers>
                                    </CheckBox>

But I am always getting null in the parameter of my command's execute method. I have tried with other properties of DataGrid such as Width, ActualHeight e.t.c. but of no use. What am I missing here ?