Force WPF BitmapImage to reload from its UriSource

Question

I am trying to build a custom control, based on Image, which simply makes the image reload (from the same URI) on a timer. The original image is displaying fine, but it doesn't seem to refresh.

And here is custom control:

public class RefreshImage : Image
{
    protected override void OnInitialized(EventArgs e)
    {
        base.OnInitialized(e);
        this.Loaded += RefreshImage_Loaded;
    }

    private void RefreshImage_Loaded(object sender, RoutedEventArgs e)
    {
        var timer = new DispatcherTimer();
        timer.Interval = TimeSpan.FromSeconds(1);
        timer.Tick += RefreshImage_Tick;
        timer.Start();
    }

    private void RefreshImage_Tick(object sender, System.EventArgs e)
    {
        var bm = (BitmapImage) Source;
        bm.InvalidateProperty(BitmapImage.UriSourceProperty);
    }
 }

And I'm using it like so:

  <custom:RefreshImage>
      <Image.Source>
          <BitmapImage UriCachePolicy="NoCacheNoStore"
                       CreateOptions="IgnoreImageCache" CacheOption="None"
                       UriSource="{Binding Uri}"/>
      </Image.Source>
  </custom:RefreshImage>

Documentation for InvalidateProperty seems to indicate it's exactly what I need:

You can also use InvalidateProperty to force re-evaluation of a binding against a data source that is not able to implement the recommended INotifyPropertyChanged notification mechanism.

Raising an INotifiyPropertyChanged.PropertyChanged event on the Uri also does not trigger the image to reload.

Answer 1

Seems that BitmapSource are, in general, immutable objects. Once they have finished being initialized any further property changes are ignored. I suspect this includes the UriSource.

This following phase is repeated often in this MSDN post on creating custom ImageSources:

The ISupportInitialize interface is used to snap the values of the properties when initialization is complete. Further changes to the properties are ignored.