C＃Wpf自定义转换器已创建但未调用

Question

I've got XAML parse exception "BitmapImage UriSource must be set". While parsing, my converter is created, but Convert() method is not called. What am I doing wrong?

XAML:

<ImageBrush >
    <ImageBrush.ImageSource>
          <BitmapImage UriSource="{Binding Path=Value.Image, Converter={StaticResource imageConverter}, ConverterParameter=Value.Image}" CacheOption="OnLoad"></BitmapImage>
    </ImageBrush.ImageSource>
</ImageBrush>

C#:

public class ImageConverter : IValueConverter
{
    public ImageConverter()
    {
    }
    public object Convert(object value, Type targetType,
                      object parameter, CultureInfo culture)
    {
        try
        {
            return new BitmapImage(new Uri((string)value));
        }
        catch
        {
            return new BitmapImage();
        }
    }

    public object ConvertBack(object value, Type targetType,
                              object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Answer 1

I've found kind of solution. Since I needed to use <BitmapImage> only for setting CacheOption.OnLoad so my local source file would not be locked, I've created custom ImageConverter :

[ValueConversion(typeof(Uri), typeof(BitmapImage))]
public class ImageConverter : IValueConverter
{
    public ImageConverter()
    {
    }
    public object Convert(object value, Type targetType,
                      object parameter, CultureInfo culture)
    {
        try
        {
            if(value == null)
            {
                return null;
            }
            var image = new BitmapImage();
            image.BeginInit();
            image.UriSource = value is Uri ? (Uri)value : new Uri(value.ToString());
            image.CacheOption = BitmapCacheOption.OnLoad;
            image.EndInit();
            return image;               
        }
        catch
        {
            return null;
        }
    }

    public object ConvertBack(object value, Type targetType,
                              object parameter, CultureInfo culture)
    {
        throw new NotSupportedException("Convert back function is not supported");
    }
}

And XAML:

<ImageBrush ImageSource="{Binding Path=Value.Image, Converter={StaticResource imageConverter}}">
</ImageBrush>