C# uwp表达式节点淡入动画

我正在使用Windows UI开发实验室示例库上的示例。我在我的应用程序中使用了ShyHeader示例，但我没有使用完全相同的代码，但实际上我根据自己的需要编辑了示例。 我的问题是如何使用expression node淡入与scroll viewer相对应的特定XAML元素，我可以使用scroll viewer淡出元素。但是我不能从不透明0->不透明1淡入元素。 这是我的代码。

<ScrollViewer x:Name="MyScrollViewer">
    <Grid>
        <local:MyAdaptiveView Margin="0,300,0,0"
                  x:Name="AllVideosGridView"/>
        <Grid x:Name="Header" Height="300" VerticalAlignment="Top">
            <FlipView x:Name="MainFlipView" 
            </FlipView>
            <Grid Background="Blue" Height="150" VerticalAlignment="Bottom" Opacity="0.5" Name="FrontGrid">

            </Grid>
        </Grid>
    </Grid>
</ScrollViewer>

你的表情看起来不错

请注意，使用合成设置动画的
Opacity
是
Visual
的
Opacity
。但是，您在
FrontGrid
XAML上设置的
0.5
的
Opacity
来自
UIElement
。这样做将破坏合成不透明度表达式动画

修复方法很简单-尝试在
初始化组件后立即获取
FrontGrid
的
视觉
，并将其
不透明度设置为
0.5
（即
frontVisual.Opacity=0.5
），而不是在XAML中设置


由于XAML组合互操作行为的改变，您将从周年更新开始看到这种“奇怪”的行为

要了解完整的解释，请阅读此文

简而言之，XAML不知道合成是否改变了
不透明度
，它仍然认为它应该是
0.5
，因为它是上次设置的。因此，它将尝试覆盖并导致动画失败。另外一些属性也会出现这种情况，如
偏移量
和
大小

我的建议是，如果你去写作文，试着一路写下去。：）

        // Create a PropertySet that has values to be referenced in the ExpressionAnimations below
        _props = _compositor.CreatePropertySet();
        _props.InsertScalar("progress", 0);
        _props.InsertScalar("clampSize", 150);
        _props.InsertScalar("scaleFactor", 0.7f);

        // Get references to our property sets for use with ExpressionNodes
        var scrollingProperties = _scrollerPropertySet.GetSpecializedReference<ManipulationPropertySetReferenceNode>();
        var props = _props.GetReference();
        var progressNode = props.GetScalarProperty("progress");
        var clampSizeNode = props.GetScalarProperty("clampSize");
        var scaleFactorNode = props.GetScalarProperty("scaleFactor");

        // Create a blur effect to be animated based on scroll position
        var blurEffect = new GaussianBlurEffect()
        {
            Name = "blur",
            BlurAmount = 0.0f,
            BorderMode = EffectBorderMode.Hard,
            Optimization = EffectOptimization.Balanced,
            Source = new CompositionEffectSourceParameter("source")
        };

        var blurBrush = _compositor.CreateEffectFactory(
            blurEffect,
            new[] { "blur.BlurAmount" })
            .CreateBrush();

        blurBrush.SetSourceParameter("source", _compositor.CreateBackdropBrush());

        // Create a Visual for applying the blur effect
        _blurredBackgroundImageVisual = _compositor.CreateSpriteVisual();
        _blurredBackgroundImageVisual.Brush = blurBrush;
        _blurredBackgroundImageVisual.Size = new Vector2((float)Header.ActualWidth, (float)Header.ActualHeight);

        // Insert the blur visual at the right point in the Visual Tree
        ElementCompositionPreview.SetElementChildVisual(Header, _blurredBackgroundImageVisual);

        // Create and start an ExpressionAnimation to track scroll progress over the desired distance
        ExpressionNode progressAnimation = EF.Clamp(-scrollingProperties.Translation.Y / clampSizeNode, 0, 1);
        _props.StartAnimation("progress", progressAnimation);

        // Create and start an ExpressionAnimation to animate blur radius between 0 and 15 based on progress
        ExpressionNode blurAnimation = EF.Lerp(0, 15, progressNode);
        _blurredBackgroundImageVisual.Brush.Properties.StartAnimation("blur.BlurAmount", blurAnimation);

        // Get the backing visual for the header so that its properties can be animated
        Visual headerVisual = ElementCompositionPreview.GetElementVisual(Header);

        // Create and start an ExpressionAnimation to clamp the header's offset to keep it onscreen
        ExpressionNode headerTranslationAnimation = EF.Conditional(progressNode < 1, 0, -scrollingProperties.Translation.Y - clampSizeNode);
        headerVisual.StartAnimation("Offset.Y", headerTranslationAnimation);

        // Create and start an ExpressionAnimation to scale the header during overpan
        ExpressionNode headerScaleAnimation = EF.Lerp(1, 1.25f, EF.Clamp(scrollingProperties.Translation.Y / 50, 0, 1));
        headerVisual.StartAnimation("Scale.X", headerScaleAnimation);
        headerVisual.StartAnimation("Scale.Y", headerScaleAnimation);

        //Set the header's CenterPoint to ensure the overpan scale looks as desired
        headerVisual.CenterPoint = new Vector3((float)(Header.ActualWidth / 2), (float)Header.ActualHeight, 0);

        // Get the backing visual for the photo in the header so that its properties can be animated
        Visual photoVisual = ElementCompositionPreview.GetElementVisual(MainFlipView);

        // Create and start an ExpressionAnimation to opacity fade out the image behind the header
        ExpressionNode imageOpacityAnimation = 1 - progressNode;
        photoVisual.StartAnimation("opacity", imageOpacityAnimation);

        // Get the front visual for the photo in the header so that its properties can be animated
        Visual frontVisual = ElementCompositionPreview.GetElementVisual(FrontGrid);

        // Create and start an ExpressionAnimation to opacity fade out the image behind the header
        ExpressionNode imageOpacityAnimation2 = 0 + progressNode;
        frontVisual.StartAnimation("opacity", imageOpacityAnimation2);
    }