ListBox bound to ObservableCollection not refreshing on view loaded - wpf

Question

I have the following XAML containing a ListBox bound to an ObservableCollection
<ListBox
Margin="0,5"
Grid.Row="1"
Grid.ColumnSpan="3"
Visibility="{Binding ArePicturesAvailable, Converter={StaticResource BoolToVisConv}}"
SelectedItem="{Binding SelectedPicture}"
ItemsSource="{Binding Pictures, NotifyOnSourceUpdated=True}"
ScrollViewer.VerticalScrollBarVisibility="Disabled">
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<WrapPanel Orientation="Vertical" />
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemTemplate>
<DataTemplate>
<Image Margin="8"
Height="{Binding Size.Height}"
Width="{Binding Size.Width}"
Source="{Binding FullPath, Converter={StaticResource RelativeToFullConv}}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Since there is noticeable delay in populating the ListBox, I am attempting to defer this until the ListBox's containing view has loaded using Dispatcher.BeginInvoke as illustrated below:
public class PictureMarkerEditorViewModel
{
private PictureSelectorViewModel _pictureSelectorViewModel;
public string PhotoCollectionDirectory { get; set; }
protected ISymbolEditor GetEditorImpl(ISymbolInfo symbolInfo)
{
var picSymbolInfo = (PictureMarkerSymbolInfo)symbolInfo;
_pictureSelectorViewModel = new PictureSelectorViewModel(picSymbolInfo);
var editor = new PictureMarkerSymbolEditor(_pictureSelectorViewModel, picSymbolInfo);
editor.Dispatcher.BeginInvoke(DispatcherPriority.Background, new Action(() =>
{
var photos = GetPhotoCollection();
_pictureSelectorViewModel.Pictures.AddRange(photos);
}));
//var photos = GetPhotoCollection();
//_pictureSelectorViewModel.Pictures.AddRange(photos);
return editor;
}
public IEnumerable<Picture> GetPhotoCollection()
{
if (string.IsNullOrEmpty(PhotoCollectionDirectory))
return null;
if (!Directory.Exists(PhotoCollectionDirectory))
throw new ArgumentException("Cannot show images from invalid directory " + PhotoCollectionDirectory + ".");
var files = Directory.GetFiles(PhotoCollectionDirectory, "*.png", SearchOption.AllDirectories);
return files.Select(f => new Picture(Path.GetFileName(f), f, ImageUtils.GetDimensions(f)));
}
}
where PictureSelectorViewModel.Pictures is simply an ObservableCollection of Picture:
public class PictureSelectorViewModel
{
private readonly ObservableCollection<Picture> _pictures= new ObservableCollection<Picture>();
public ObservableCollection<Picture> Pictures
{
get
{
return _pictures;
}
}
}
and Picture is a simple class containing Name and FullPath properties:
public class Picture
{
public string Name { get;set}
public string FullPath {get; set;}
public Size Size {get;set;}
}
I simply cannot get the list populated after it has loaded. If I populate the Pictures collection before the view is loaded (the commented part of the code, I see the images.
Any one know why?
TIA.