为什么在 WinRT 中为枚举依赖属性设置默认值会失败？

Question

我正在尝试使用枚举作为依赖属性的类型，但任何默认设置似乎都失败了。

编译成功，但是当我尝试在 XAML 中使用该对象时，我收到“Specified Cast is not Valid”错误，并且我的对象上有蓝色下划线。

VS2012 使用 WinRT。

我做错了什么？

这是我正在使用的代码：

public class WheelPanel : Panel
{
    public enum ItemAlignmentOptions
    {
        Left, Center, Right
    }

    /// <summary>
    /// Identifies the <see cref="ItemAlignment" /> dependency property.
    /// </summary>

    // This fails using null

    //public static readonly DependencyProperty ItemAlignmentProperty = DependencyProperty.Register(
    //    ItemAlignmentPropertyName,
    //    typeof(ItemAlignmentOptions),
    //    typeof(WheelPanel),
    //    new PropertyMetadata(null,new PropertyChangedCallback(ItemAlignmentChanged)));

    // This fails using a default value

    //public static readonly DependencyProperty ItemAlignmentProperty = DependencyProperty.Register(
    //    ItemAlignmentPropertyName,
    //    typeof(ItemAlignmentOptions),
    //    typeof(WheelPanel),
    //    new PropertyMetadata(ItemAlignmentOptions.Center,new PropertyChangedCallback(ItemAlignmentChanged)));

    // This works!
    public static readonly DependencyProperty ItemAlignmentProperty = DependencyProperty.Register(
        ItemAlignmentPropertyName,
        typeof(ItemAlignmentOptions),
        typeof(WheelPanel),
        new PropertyMetadata(new PropertyChangedCallback(ItemAlignmentChanged)));

    /// <summary>
    /// The <see cref="ItemAlignment" /> dependency property's name.
    /// </summary>
    public const string ItemAlignmentPropertyName = "ItemAlignment";

    /// <summary>
    /// Gets or sets the value of the <see cref="ItemAlignment" />
    /// property. This is a dependency property.
    /// </summary>
    public ItemAlignmentOptions ItemAlignment
    {
        get { return (ItemAlignmentOptions)GetValue(ItemAlignmentProperty); }
        set { SetValue(ItemAlignmentProperty, value); }
    }

Answer 1

尝试使用“1”作为值。枚举的底层类型是 Int32（默认），也许它需要一个整数作为默认值。