为什么不保留Translation属性（Composition）？

Question

我有以下代码将矩形下移100px ，然后完成翻译，将矩形右100px 平移，但是我希望向右平移以保持动画Y （100像素），但是它不会那样做。调试时，我注意到Translation的值为（0,0,0）而不是（0,100,0）。

这是我应用程序中的代码（应用程序必须具有UWP目标+最低sdk 17763 ）：

public MainPage()
{
    this.InitializeComponent();

    this.Loaded += (sender1, e1) =>
    {
        var compositor = Window.Current.Compositor;
        var batch = compositor.CreateScopedBatch(Windows.UI.Composition.CompositionBatchTypes.Animation);

        var vertical = compositor.CreateVector3KeyFrameAnimation();

        vertical.InsertKeyFrame(1.0f, new Vector3(0f, 100f, 0f));
        vertical.Duration = TimeSpan.FromMilliseconds(2000);
        vertical.Target = "Translation";

        Rect.StartAnimation(vertical);

        batch.End();

        batch.Completed += (sender2, e2) =>
        {
            var horizontal = compositor.CreateVector3KeyFrameAnimation();

            // PROBLEM: ... Rect.Translation.Y is not 100, it's 0 ...
            horizontal.InsertKeyFrame(1.0f, new Vector3(100f, Rect.Translation.Y, 0f));
            horizontal.Duration = TimeSpan.FromMilliseconds(2000);
            horizontal.Target = "Translation";

            Rect.StartAnimation(horizontal);
        };
    };
}

完成初始动画后，保持Y位置的正确方法是什么？

Answer 1

我很确定 Johhny Westlake 有一个有效的答案，但是我通过以下方法解决了我的问题：

this.Loaded += (sender1, e1) =>
{
    var compositor = Window.Current.Compositor;

    ElementCompositionPreview.SetIsTranslationEnabled(Rect, true);
    var visual = ElementCompositionPreview.GetElementVisual(Rect);
    var batch = compositor.CreateScopedBatch(Windows.UI.Composition.CompositionBatchTypes.Animation);

    var vertical = compositor.CreateScalarKeyFrameAnimation();

    vertical.InsertKeyFrame(1.0f, 100f);
    vertical.Duration = TimeSpan.FromMilliseconds(2000);

    visual.StartAnimation("Translation.Y", vertical);

    batch.End();

    batch.Completed += (sender2, e2) =>
    {
        var horizontal = compositor.CreateScalarKeyFrameAnimation();

        horizontal.InsertKeyFrame(1.0f, 100f);
        horizontal.Duration = TimeSpan.FromMilliseconds(2000);

        visual.StartAnimation("Translation.X", horizontal);
    };
};