Listbox default image - silverlight

Question

In an windows phone 7 application I'm populating one listbox with remote images .. since the images are not downloaded instantly I want to load a default image until the remote image are ready. What is the best way to do this?
Until now, I have the following code skelton:
public partial class RemoteImage : PhoneApplicationPage
{
ObservableCollection<Image> images = new ObservableCollection<Image> { };
public RemoteImage()
{
InitializeComponent();
listImage.ItemsSource = GetAllImages();
}
private ImageSource GetImageSource(string fileName)
{
return new BitmapImage(new Uri(fileName, UriKind.Absolute));
}
private ObservableCollection<Image> GetAllImages()
{
WebClient restClient = new WebClient();
restClient.OpenReadAsync(new Uri(#"http://www.my-api.com"));
restClient.OpenReadCompleted += new OpenReadCompletedEventHandler(onReadComplete);
return images;
}
private void onReadComplete(object sender, OpenReadCompletedEventArgs args)
{
Stream stm = args.Result;
DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(RootObject));
RootObject ro = (RootObject)ser.ReadObject(stm);
foreach (var item in ro.items)
{
images.Add(new Image{ PhotoSource = GetImageSource(item.image.link) });
}
}
}

Answer 1

If you know, how many images you would need, you should create first the number of default images. Load some image file directly at your project and use it as imageSource for default images. Then, when you'll finish downloading remote images, you should set the new image source for each.
When I got the similar issue, I had some problems with defining which exactly downloaded image refers to which object on page. (As you remember the WebClient objects work asynchronously, so if you have 10 images on page and download 10 remote images at once you can't say that the first downloaded image is the first on page) To solve this you could create more complicated download method (I used a delegate to transfer the id/name of image) or use recursion (Start download method for first image, download it, set source for one on page, download next one...).