我正在创建一个包装TreeView元素的UserControl (让我们称之为ViewTree)。在ViewTree.xaml.cs中，我有一个 Source 依赖属性：

public static readonly DependencyProperty SourceProperty
    = DependencyProperty.Register (
        "Source",
        typeof (ObservableCollection<TreeItem>),
        typeof (ViewTree),
        new FrameworkPropertyMetadata (new ObservableCollection<TreeItem>(), OnSourceChanged)
public ObservableCollection<TreeItem> Source
    get { return (ObservableCollection<TreeItem>)GetValue(SourceProperty); }
    set { SetValue(SourceProperty, value); }
}

此UserControl的使用者可以执行输入绑定的...so：

<features:ViewTree Source="{Binding Path=...}">

然而，在ViewTree UserControl中，我并不想直接绑定到这个DependencyProperty。相反，我想绑定到ViewModel中的另一个属性(使用棱镜)，所以我在ViewTree.xaml.cs中这样做：

private static void OnSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    var nextTreeSource = e.NewValue as ObservableCollection<TreeItem>;
    if (nextTreeSource == null)
        return;
    var viewTree = d as ViewTree;
    viewTree.UpdateTreeSource(nextTreeSource);