问在非UI线程中填充WP7后，ObservableCollection中的跨线程访问无效

EN

public partial class MainPage : PhoneApplicationPage
{
    private ObservableCollection<string> obrazkiFinal = new ObservableCollection<string>();

    public ObservableCollection<string> ObrazkiFinal
    {
        get { return obrazkiFinal; }
        set { obrazkiFinal = value; }
    }

    // Constructor
    public MainPage()
    {
        InitializeComponent();
    }

    private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
    {
        lBox.ItemsSource = ObrazkiFinal;

        HttpWebRequest httpRequest = WebRequest.CreateHttp(@"http://website");
        IAsyncResult res = httpRequest.BeginGetResponse(new AsyncCallback(RespResult),httpRequest);
    }

    private void RespResult(IAsyncResult respResylt)
    {
        var res = (HttpWebRequest)respResylt.AsyncState;
        var resp = res.EndGetResponse(respResylt);

        /* some parsing code */
         foreach (/* found pic urls */)
         {
             //new httpwebrequest
             HttpWebRequest picHttpRequest = WebRequest.CreateHttp(picUrl);
             IAsyncResult picRes = picHttpRequest.BeginGetResponse(DownloadImageResult, picHttpRequest );

       }

    private void DownloadImageResult(IAsyncResult result)
    {
        var res = state.HttpWebRequest;
        var resp = res.EndGetResponse(result);

        /*some saving code*/

        Dispatcher.BeginInvoke(() => { ObrazkiFinal.Add(fileName); });
     }
    }
}

<ListBox Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Height="Auto" Name="lBox">
 <ListBox.ItemTemplate>
     <DataTemplate>
        <StackPanel>
              <Image Source="{Binding}"></Image>
        </StackPanel>
     </DataTemplate>
 </ListBox.ItemTemplate>
</ListBox>

DataContext="{Binding RelativeSource={RelativeSource Self}}"