WPF Datagrid Binding

Hello

I have following code in xaml:

<DataGrid AutoGenerateColumns="False" HorizontalGridLinesBrush="Black" IsReadOnly="False"
          ItemsSource="{Binding AccessList, Mode=TwoWay}" Margin="5,8,5,0" Name="dgAccess">
    <DataGrid.Columns>
        <DataGridTemplateColumn Header="Group">
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <ComboBox
                        SelectedItem="{Binding Path=UserGroup, Mode=TwoWay}"
                        ItemsSource="{Binding Path=DataContext.UserGroupList,
                        RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"
                        IsReadOnly="False" Background="White" />
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns

The grid has a list of objects (List<doctypeaccess>).
The ComboBox in the datagrid has a list of objects (List<usergroup>).

When i select a group in a row, the binding sould set the property UserGroup in my object AccessList. But it not works. The AccessList.UserGroup is always null?

Class DocTypeAccess

public class DocTypeAccess
{
    public UserGroup UserGroup { get; set; }
}

Binding Property on ViewModel

public List<DocTypeAccess> AccessList
{
    get { return m_listAccess; }
    set
    {
        m_listAccess = value;
        OnPropertyChanged("AccessList");
    }
}

What make i wrong?

Thanks for your help...

Tags: C#, WPF, Combobox, DataGrid