How do I implement Silverlight DataGrid ComboBox to maintain the Selected item on each row

See more:

C#

C#4.0

Silverlight4

Dear All,

I want to select an Item from a combobox within a Datagrid in Silverlight. But when I select an Item on any row, all the rows show the same Item. The XAML is shown below:

<navigation:page x:class="ChinaAfricaCotton.Views.TestPage" xmlns:x="#unknown" xmlns:navigation="#unknown">
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
           xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
           xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
           mc:Ignorable="d"
           xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"
           d:DesignWidth="640" d:DesignHeight="480"
           Title="TestPage Page" 
           xmlns:riaControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.DomainServices"
           xmlns:my="clr-namespace:ChinaAfricaReportLibrary" 
           xmlns:my1="clr-namespace:ChinaAfricaCotton.Web.DomainServices" 
           xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

    <usercontrol.resources>
        <riacontrols:domaindatasource autoload="False" xmlns:riacontrols="#unknown">
                                      LoadedData="tblItemDomainDataSource_LoadedData" 
                                     x:Name="tblItemDomainDataSource" 
                                      QueryName="GetTblItemsQuery">            
        </riacontrols:domaindatasource>
           
    </usercontrol.resources>
    <grid x:name="LayoutRoot">
        <sdk:datagrid x:name="datagrid1" grid.row="0" autogeneratecolumns="False" xmlns:sdk="#unknown">
            <sdk:datagrid.columns>
                <sdk:datagridtextcolumn header="Item Code" binding="{Binding ItemCode}" />
                <sdk:datagridtextcolumn header="Item Name" binding="{Binding ItemName}" />                
                <sdk:datagridtextcolumn header="Category" binding="{Binding tblCategory.CategoryName}" />

                <sdk:datagridtemplatecolumn header="Item Name">
                    
                    <sdk:datagridtemplatecolumn.celleditingtemplate>
                        <datatemplate>
                            <combobox x:name="cmbItemName">
                                ItemsSource="{Binding Data, Source={StaticResource tblItemDomainDataSource}}" 
                                SelectedValuePath="ItemCode"
                                DisplayMemberPath="ItemName"
                                
                                SelectedValue="{Binding Path=ItemCode, Mode=TwoWay}" />
                        </combobox></datatemplate>
                    </sdk:datagridtemplatecolumn.celleditingtemplate>
                </sdk:datagridtemplatecolumn>

                
            </sdk:datagrid.columns>
        </sdk:datagrid>

    </grid>
</navigation:page>

Can someone help me please? I need this to work like yesterday....!