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

```xml
<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` etc. but of no use. What am I missing here?