如何创建自定义WPF集合?

我正在尝试创建一组自定义类,这些类可以通过XAML添加到WPF控件中。

我遇到的问题是向集合中添加项。这是我到目前为止所拥有的。

public class MyControl : Control
{
    static MyControl()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(MyControl), new FrameworkPropertyMetadata(typeof(MyControl)));
    }

    public static DependencyProperty MyCollectionProperty = DependencyProperty.Register("MyCollection", typeof(MyCollection), typeof(MyControl));
    public MyCollection MyCollection
    {
        get { return (MyCollection)GetValue(MyCollectionProperty); }
        set { SetValue(MyCollectionProperty, value); }
    }
}

public class MyCollectionBase : DependencyObject
{
    // This class is needed for some other things...
}

[ContentProperty("Items")]
public class MyCollection : MyCollectionBase
{
    public ItemCollection Items { get; set; }
}

public class MyItem : DependencyObject { ... }

和XAML。

<l:MyControl>
    <l:MyControl.MyCollection>
        <l:MyCollection>
            <l:MyItem />
        </l:MyCollection>
    </l:MyControl.MyCollection>
</l:MyControl>

例外情况是:
System.Windows.Markup.XamlParseException occurred Message="'MyItem' object cannot be added to 'MyCollection'. Object of type 'CollectionTest.MyItem' cannot be converted to type 'System.Windows.Controls.ItemCollection'.

有人知道我怎么修这个吗?谢谢