DataGridComboBoxColumn初始值

Question

我无法绑定WPF DataGridComboBoxColumn并设置初始值。我可以使用集合中的数据填充组合框，但我似乎无法设置初始值。

    <DataGridComboBoxColumn Header="Target Account Number" 
ItemsSource="{Binding Account.RawAccountNumber}"
                            SelectedValueBinding="{Binding Account.RawAccountNumber, Mode=TwoWay}"  
                            DisplayMemberPath="RawAccountNumber" 
                            SelectedValuePath="RawAccountNumber">
        <DataGridComboBoxColumn.ElementStyle>
            <Style TargetType="ComboBox">
                <Setter Property="ItemsSource" 
                        Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.Accounts}"/>
            </Style>
        </DataGridComboBoxColumn.ElementStyle>
        <DataGridComboBoxColumn.EditingElementStyle>
            <Style TargetType="ComboBox">
                <Setter Property="ItemsSource" 
                        Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.Accounts}"/>
            </Style>
        </DataGridComboBoxColumn.EditingElementStyle>
    </DataGridComboBoxColumn>

我尝试更改ItemSource，但这会导致组合框变空。

我看过several SO posts但这些都没有给我带来答案。请有人帮我指点正确的方向吗？

UPDATE 我打算包含我的datagrid定义，显示Grid的ItemSource。

<DataGrid x:Name="dataGrid" DataGridCell.Selected="DataGrid_GotFocus" AutoGenerateColumns="False" HorizontalAlignment="Left" Margin="10,51,0,0" VerticalAlignment="Top" Height="521" Width="862" ItemsSource="{Binding Transaction.Rows}">