Add a readonly Image
property to your Zipfile class, and move the converter code to the property getter:
public class Zipfile
{
...
public ImageSource Image
{
get
{
Compressor.Unzip(this);
var uri = string.Format("{0}{1}.jpg", Compressor.TempPath, this.ToString());
return new BitmapImage(new Uri(uri));
}
}
}
Then write your binding like this:
<Image Source="{Binding Path=CurrentItem.Image, IsAsync=True}"/>