为什么未在DataGrid中更新ItemsSource

我的窗口使用MyUserControl，并通过MyItemsProperty属性向其传递一组项。MyUserControl将项转换为MyClassBag，并将项添加到绑定到DataGrid的ItemsSource的WrappedItems集合（OnMyItemsChanged->CollectionChanged->AddItem）。

问题是ItemsSource没有更新（我在control.WrappedItems.Add(new MyClassBag { ... });上设置了一个制动点，它确实到达了那里）
但是，如果我在MyUserControl中放置一个按钮，并通过按钮的单击方法添加项目（WrappedItems.Add(new MyClassBag { ... });），则ItemsSource确实会得到更新。问题出在哪里？

public partial class MyUserControl : UserControl
{
    public static readonly DependencyProperty MyItemsProperty =             
      DependencyProperty.Register("MyItems",
         typeof(ObservableCollection<MyClass>), 
         typeof(MyUserControl),
         new PropertyMetadata(
            new ObservableCollection<MyClass>(),
            new PropertyChangedCallback(OnMyItemsChanged)
         )
      );
    public ObservableCollection<MyClass> MyItems
    {
        get { return (ObservableCollection<MyItems>)GetValue(MyItemsProperty); }
        set { SetValue(MyItemsProperty, value); }
    }
    private static void OnMyItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        control = d as MyUserControl;
        var items = e.NewValue as ObservableCollection<MyClass>;
        states.CollectionChanged += new NotifyCollectionChangedEventHandler(CollectionChanged);
        AddItem(control, items);
    }
    private static void CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        var items = sender as ObservableCollection<MyClass>;
        if (e.Action == NotifyCollectionChangedAction.Add)
        {
            control.AddNewItem();
        }
    }
    public ObservableCollection<MyClassBag> WrappedItems { get; set; }
    public void AddNewItem()
    {
        WrappedItems.Add(new MyClassBag { ... });
    }
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        AddNewItem();
    }
}

MyUserControl.XAML

<DataGrid ItemsSource="{Binding WrappedItems ... />
<Button Click="Button_Click" />

Window.cs

public partial class Window1 : Window
{
    public ObservableCollection<MyClass> ItemsForMyUserControl { get; set; }
    private void Load()
    {
         ItemsForMyUserControl.Add(new MyClass(...));
         ItemsForMyUserControl.Add(new MyClass(...));
    }
}

窗口.xaml

<uc:MyUserControl MyItems="{Binding ItemsForMyUserControl}" />