Caliburn Micro不更新用户控件中的依赖项属性

Question

I have a Caliburn Micro View/ViewModel set which is utilizing a User Control which has one of its dependency properties bound to a value which is in the ViewModel of the main view. I can't seem to get the User Control to be notified when the value in the ViewModel changes.

ViewModel:

OutputImage.AddDirtyRect(new Int32Rect(0, 0, width, height));
OutputImage.Unlock();

NotifyOfPropertyChange(() => OutputImage);

Main View:

<local:HistogramControl x:Name="Histogram" Grid.Row="1" Grid.Column="0" OutputImage="{Binding Path=OutputImage, Mode=TwoWay}"/>

User Control:

    public static readonly DependencyProperty OutputImageProperty =
    DependencyProperty.Register("OutputImage", typeof(BitmapSource), typeof(HistogramControl), new UIPropertyMetadata(
            new WriteableBitmap(1, 1, 96, 96, PixelFormats.Rgb24, null),
            new PropertyChangedCallback((s, e) =>
            {
                var source = s as HistogramControl;
                source.UpdateHistogram();
            })));
    public BitmapSource OutputImage
    {
        get { return (BitmapSource)GetValue(OutputImageProperty); }
        set { SetValue(OutputImageProperty, value); }
    }

If I place a break point in the user control code in the PropertyChangedCallback(...) lambda it will be hit once when the application starts and the initial OutputImage set in the constructor of the ViewModel class is provided, but it will not be called again when the ViewModel code shown above is called and the OutputImage changes.

Answer 1

The problem is that the WriteableBitmap was modified via pointers to its memory in unsafe code since image data was being copied into the pixel buffer. This didn't trigger a binding update since the object bound wasn't really updated. Since the binding is via reference the pixel data in the bound value inside the user control was updated as it was changed, there just was no notification via a call to the PropertyChangedCallback(...) .