WPF绑定问题

我在XAML/WPF中绑定有问题。 我创建了扩展FrameworkElement的Action类。每个操作都有ActionItem列表。问题是ActionItem的Data/DataContext属性没有设置,所以它们总是空的。

XAML编号:

<my:Action DataContext="{Binding}">
    <my:Action.Items>
        <my:ActionItem DataContext="{Binding}" Data="{Binding}" />
    </my:Action.Items>
</my:Action>

C#:

public class Action : FrameworkElement
{
    public static readonly DependencyProperty ItemsProperty =
        DependencyProperty.Register("Items", typeof(IList), typeof(Action), 
                                    new PropertyMetadata(null, null), null);

    public Action()
    {
        this.Items = new ArrayList();
        this.DataContextChanged += (s, e) => MessageBox.Show("Action.DataContext");
    }

    public IList Items
    {
        get { return (IList)this.GetValue(ItemsProperty); }
        set { this.SetValue(ItemsProperty, value); }
    }
}

public class ActionItem : FrameworkElement
{
    public static readonly DependencyProperty DataProperty =
        DependencyProperty.Register("Data", typeof(object), typeof(ActionItem),
            new PropertyMetadata(
                null, null, (d, v) =>
                {
                    if (v != null)
                        MessageBox.Show("ActionItem.Data is not null");
                    return v;
                }
            ), null
        );

    public object Data
    {
        get { return this.GetValue(DataProperty); }
        set { this.SetValue(DataProperty, value); }
    }

    public ActionItem()
    {
        this.DataContextChanged += (s, e) => MessageBox.Show("ActionItem.DataContext");
    }
}