[WPF] ComboBox: error multiConverter and Selected Item

Question

Hi,


in my datagrid I insert a TextBlock and ComboBox for edit cell.


When I click in the cell for edit and I select an item of combox:
1) the item selected is not shown in cell of DataGrid.
2) my Convert is called two times.


Why?


XAML


<DataGridTemplateColumn Header="{StaticResource datagridDay}">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding Day, Mode=TwoWay}" />
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ComboBox Name="dgCmbDay" DataContext="{Binding}">
<ComboBox.ItemsSource>
<MultiBinding Converter="{StaticResource DateNumNameConverter}" >                                            
<MultiBinding.Bindings>                                                
<Binding ElementName="dgPlan" Path="CurrentItem"/>
<Binding Source="{StaticResource AnalysisPlanViewModel}" Path="ListDayNameOfWeek"/>
<Binding Source="{StaticResource AnalysisPlanViewModel}" Path="ListDayNumOfMonth"/>                                                
<Binding Path="Items"></Binding>
</MultiBinding.Bindings>
</MultiBinding>
</ComboBox.ItemsSource>
</ComboBox>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>
My Converter:


    public class DayNumName : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            if (values == null || values.Length < 4)
                return null;


            AnalysisPlanItemExt analisysPlanItem = (AnalysisPlanItemExt)values[0];
            List<string> listDayOfWeek = (List<string>)values[1];
            List<string> listDayNumOfMonth = (List<string>)values[2];


            if (analisysPlanItem.Type != null)
            {
                //Day of Weeks
                if (analisysPlanItem.Type.Value.Equals(Definition.SchedTypeEnum.DayOfWeek))
                    return listDayOfWeek;


                if (analisysPlanItem.Type.Value.Equals(Definition.SchedTypeEnum.DayOfMonth))
                    return listDayNumOfMonth;
            }


            return null;
        }


        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new System.NotImplementedException();
        }
    }
Thanks!