WPF SurfaceButton在点击时放下SurfaceScrollViewer

Question

正如标题所说，我希望有一个基础为SurfaceButton的组件，点击后会下拉SurfaceScrollViewer。我认为我已经做了正确的第一步，但SurfaceScrollViewer永远不会变得可见，它似乎也没有显示在Blend的层次结构中。我是否错误地访问或初始化了某些内容？我有多个SurfaceDropDown对象实例作为StackPanel的子项，它是另一个SurfaceScrollViewer的内容。此父级滚动查看器在网格中对齐，这就是我使用ActualHeight / Width属性设置高度和宽度的原因。

public class SurfaceDropDown : SurfaceButton
{
    public SurfaceScrollViewer scrollViewer;
    private StackPanel stackPanel;

    public SurfaceDropDown()
    {
        this.Click += OnClick;

        scrollViewer = new SurfaceScrollViewer();

        scrollViewer.Height = this.ActualHeight * 5.0;
        scrollViewer.Width = this.ActualWidth;

        scrollViewer.HorizontalAlignment = System.Windows.HorizontalAlignment.Center;
        scrollViewer.VerticalAlignment = System.Windows.VerticalAlignment.Center;
        scrollViewer.HorizontalScrollBarVisibility = ScrollBarVisibility.Disabled;
        scrollViewer.VerticalScrollBarVisibility = ScrollBarVisibility.Auto;

        stackPanel = new StackPanel();

        for (int i = 0; i < 5; ++i)
        {
            Label label = new Label();

            label.Content = "Label " + i.ToString();

            stackPanel.Children.Add(label);
        }

        scrollViewer.Content = stackPanel;

        scrollViewer.ScrollChanged += OnScroll;

        this.AddChild(scrollViewer);
    }

    private void OnClick(object sender, RoutedEventArgs e)
    {
        scrollViewer.Visibility = scrollViewer.Visibility != Visibility.Visible ? Visibility.Visible : Visibility.Collapsed;
    }

    private void OnScroll(object sender, RoutedEventArgs e)
    {
    }
}

非常感谢任何帮助和/或建议！