依赖项属性–WinRT DependencyProperty,IEnumerable根本没有触发

我已经仔细搜索过了,因为我知道有很多关于依赖属性的内容,但我还没有看到任何有效的解决方案.我正在尝试将ObservableCollection从我的ViewModel绑定到我的AutoCompleteBox.我的ViewModel正在返回数据,Getter正在被击中.但是,之后,控件的SetValue或OnItemsSourcePropertyChanged不会触发.有什么可能是错的想法吗？

我有一个像这样的控件：

[ContentProperty(Name = "ItemsSource")]
public partial class AutoCompleteBox : Control
{
    //local stuff
    private ListBox lb;
    private List<Person> _items;
    private ObservableCollection<Person> _view;

    public AutoCompleteBox() : base()
    {
        DefaultStyleKey = typeof(AutoCompleteBox);
        Loaded += (sender,e) => ApplyTemplate();
    }
    protected override void OnApplyTemplate()
    {
        this.lb = this.GetTemplateChild("Selector") as ListBox;
        base.OnApplyTemplate();

    }
    #region ItemsSource

    public IEnumerable ItemsSource
    {
        get { return GetValue(ItemsSourceProperty) as ObservableCollection<Person>; }
        set { SetValue(ItemsSourceProperty,value); } //Never gets called
    }

    public static readonly DependencyProperty ItemsSourceProperty =
        DependencyProperty.Register(
            "ItemsSource",typeof(IEnumerable),typeof(AutoCompleteBox),new PropertyMetadata(null,OnItemsSourcePropertyChanged));

    private static void OnItemsSourcePropertyChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
    {
       //Never gets called :(
    }
    #endregion

    public String SearchText
    {
        get { return GetValue(SearchTextProperty) as String; }
        set
        {
            SetValue(SearchTextProperty,value);
        }
    }


    public static readonly DependencyProperty SearchTextProperty =
        DependencyProperty.Register(
            "SearchText",typeof(String),OnSearchTextPropertyChanged));

    private static void OnSearchTextPropertyChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
    {
         //gets fired when loaded,with data being bound
    }

}

以下是它如何使用控件：

<toolkit:AutoCompleteBox Grid.Row="5" Grid.Column="2" ItemsSource="{Binding Persons,Mode=TwoWay}" SearchText="WhatTheHell"/>

作为测试并且为了简单起见,我为SearchText创建了一个String DependencyProperty.如果我绑定SearchText,它会正常工作,调用OnSearchTextPropertyChanged：

<toolkit:AutoCompleteBox Grid.Row="5" Grid.Column="2" ItemsSource="{Binding Persons,Mode=TwoWay}" SearchText="{Binding SearchText}"/>

有没有人遇到WinRT的这些问题？或者看到我在做什么有什么问题？