DataGrid的行在写入后变为只读

Question

我有一个绑定到ObservableCollection的DataGrid的问题，如果我在OC上显式设置了一个跳过DataGrid的值[我有一个自动完成的文本框，所以当用户点击列表框条目时我将OC设置为当前选择索引到正确的AutoCompleted对象]它变为只读，如果我尝试用F2编辑它我得到这个异常：InvalidOperationException - 添加的项目不会出现在给定的索引'0'。

XAML：

<Window x:Class="LDary.Compras"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:l="clr-namespace:LDary"
    Title="Compras" Height="300" Width="300" Name="WinCompras">
<Window.Resources>
    <CollectionViewSource Source="{Binding ElementName=WinCompras, Path=AutoCSource}" x:Key="Source" Filter="CollectionViewSource_Filter" />
    <l:VisibilityToBooleanConverter x:Key="VisToBool" />
</Window.Resources>
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="*" />
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    <TextBlock Text="Articulos de la compra:" Padding="0,2"/>
    <DataGrid Grid.Row="1" AutoGenerateColumns="False" x:Name="Lista" CanUserAddRows="True" ItemsSource="{Binding ElementName=WinCompras, Path=CompraActual}">
        <DataGrid.Columns>
            <DataGridTemplateColumn Header="Nombre" x:Name="Nombre">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Nombre}"/>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
                <DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <StackPanel>
                            <TextBox Text="{Binding Nombre}" TextChanged="TextBox_TextChanged" Loaded="TextBox_Loaded" Unloaded="TextBox_Unloaded"/>
                            <Popup IsOpen="{Binding ElementName=ACLB, Path=Visibility, Mode=OneWay, Converter={StaticResource VisToBool}}">
                            <ListBox Visibility="Hidden" ItemsSource="{Binding Source={StaticResource Source}}" MouseLeftButtonUp="ListBox_MouseLeftButtonUp"
                                     Focusable="False" Loaded="ListBox_Loaded" Unloaded="ListBox_Unloaded" x:Name="ACLB">
                                <ListBox.ItemTemplate>
                                    <DataTemplate>
                                        <TextBlock Text="{Binding Nombre}"/>
                                    </DataTemplate>
                                </ListBox.ItemTemplate>
                            </ListBox>
                            </Popup>
                        </StackPanel>
                    </DataTemplate>
                </DataGridTemplateColumn.CellEditingTemplate>
            </DataGridTemplateColumn>
            <DataGridTextColumn Header="Cantidad" Binding="{Binding Cantidad}" />
            <DataGridTextColumn Header="Valor" Binding="{Binding Valor}" />
            <DataGridTextColumn Header="Referencia" Binding="{Binding Referencia}" />
            <DataGridTextColumn Header="Material" Binding="{Binding Material}" />
            <DataGridTextColumn Header="Color" Binding="{Binding Color}" />
        </DataGrid.Columns>
    </DataGrid>
    <Button Name="BtnGuardar" Content="Guardar" Padding="0,5" Grid.Row="2" />
    <Button Name="BtnReset" Content="Reiniciar" Padding="0,5" Grid.Row="3" />
</Grid>

代码隐藏：

public partial class Compras : Window, INotifyPropertyChanged
{

    public ColeccionArticulos CompraActual { get { return _CompraActual; } set { _CompraActual = value; NotifyChange("CompraActual"); } }
    public ColeccionArticulos _CompraActual;
    public ColeccionArticulos AutoCSource { get { return _AutoCSourse; } set { _AutoCSourse = value; NotifyChange("AutoCSource"); } }
    public ColeccionArticulos _AutoCSourse;
    private TextBox Txt;
    private ListBox Lst;

    public Compras()
    {
        AutoCSource = CentralStorage.Articulos;
        CompraActual = new ColeccionArticulos();
        InitializeComponent();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public void NotifyChange(String Info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(Info));
        }
    }

    private void CollectionViewSource_Filter(object sender, FilterEventArgs e)
    {
        if (Txt != null)
        {
            Articulo Ar = e.Item as Articulo;
            e.Accepted = Ar.Nombre.ToUpper().Contains(Txt.Text.ToUpper()) || Ar.Categoria.ToUpper().Contains(Txt.Text.ToUpper())
                            || Ar.Material.ToUpper().Contains(Txt.Text.ToUpper()) || Ar.Observaciones.ToUpper().Contains(Txt.Text.ToUpper())
                            || Ar.Referencia.ToUpper().Contains(Txt.Text.ToUpper()) || Ar.Color.ToUpper().Contains(Txt.Text.ToUpper());
        }
    }

    private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        CollectionViewSource CVS = (CollectionViewSource)WinCompras.FindResource("Source");
        Lst.Visibility = Txt.Text != "" ? Visibility.Visible : Visibility.Hidden;
        CVS.View.Refresh();
    }

    #region Find Template Controls
    private void TextBox_Loaded(object sender, RoutedEventArgs e)
    {
        Txt = sender as TextBox;
    }

    private void TextBox_Unloaded(object sender, RoutedEventArgs e)
    {
        Txt = null;
    }

    private void ListBox_Loaded(object sender, RoutedEventArgs e)
    {
        Lst = sender as ListBox;
    }

    private void ListBox_Unloaded(object sender, RoutedEventArgs e)
    {
        //Lst = null;
    }
    #endregion

    private void ListBox_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        //THIS IS WHERE THE PROBLEM STARTS >.<
        Articulo Ar = ((sender as ListBox).SelectedItem as Articulo);
        CompraActual[Lista.SelectedIndex] = Ar.Clone() as Articulo;
        Lista.CommitEdit();
    }
}

public class VisibilityToBooleanConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        Visibility Vis = (Visibility)value;
        switch (Vis)
        {
            case Visibility.Collapsed:
                return false;
            case Visibility.Hidden:
                return false;
            case Visibility.Visible:
                return true;
            default:
                return false;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

任何想法？