使用转换器将WPF ContextMenu绑定到ObservableCollection时出现问题

也许有更好的方法可以做到这一点，但这就是我现在的处境。我想将ContextMenu绑定到某个复杂类型的ObservableCollection。复杂类型的属性将决定菜单项中显示的图标。我知道的唯一方法是创建一个ComplexTypeToMenuItem转换器，并将其与绑定相关联。但是，一旦我将转换器添加到绑定中，上下文菜单就不会在集合发生更改时更新。如果我删除转换器并依赖ComplexType.ToString（），那么菜单项更新得很好。但是，在这种情况下没有图标。

这可以很容易地通过以下方式复制：

首先是XAML

<Window x:Class="GoddamnContextMenuPosition.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:GoddamnContextMenuPosition" 
        Title="MainWindow" Height="350" Width="525">
  <Window.Resources>
    <local:ComplexTypeToMenuItemConverter x:Key="ComplexTypeToMenuItemConverter" />
  </Window.Resources>
    <Grid>
        <TextBox Grid.Row="0" Text="Hooray">
            <TextBox.ContextMenu>
                <ContextMenu ItemsSource="{Binding Objects, Source={x:Static local:Settings.Instance}, Converter={StaticResource ComplexTypeToMenuItemConverter}}">
                </ContextMenu>
            </TextBox.ContextMenu>
        </TextBox>
        <Button Grid.Row="1" Content="Add" Height="25" Width="50" Click="Button_Click"></Button>
    </Grid>
</Window>

现在代码

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Settings.Instance.Objects.Add(new ComplexType()
        {
            Text = "NEW", Type = 4
        });
    }
}
public class ComplexType
{
    public ComplexType()
    {
        this.TimeStamp = DateTime.Now;
    }
    public string Text
    {
        get;
        set;
    }
    public int Type
    {
        get;
        set;
    }
    public DateTime TimeStamp
    {
        get;
        set;
    }
}
public class ComplexTypeToMenuItemConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var values = value as IEnumerable<ComplexType>;
        if (values == null)
        {
            return new List<MenuItem>
            {
                new MenuItem
                {
                    Header = "Unknown Value"
                }
            };
        }
        IList<MenuItem> items = new List<MenuItem>();
        foreach (ComplexType obj in values)
        {
            BitmapImage bitmap = new BitmapImage();
            bitmap.BeginInit();
            bitmap.UriSource = new Uri("1.png", UriKind.Relative);
            bitmap.EndInit();
            Image image = new Image();
            image.Width = 16;
            image.Source = bitmap;
            MenuItem menuItem = new MenuItem();
            menuItem.Header = string.Format("{0} - {1}", obj.Text, obj.TimeStamp.ToShortTimeString());
            menuItem.Icon = image;
            items.Add(menuItem);
        }
        return items;
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}
public class Settings
{
    private static readonly Settings settings = new Settings();
    private Settings()
    {
        this.Objects = new ObservableCollection<ComplexType>
        {
            new ComplexType
            {
                Text = "Item #1",
                Type = 1
            }
        };
    }
    public static Settings Instance
    {
        get
        {
            return settings;
        }
    }
    public ObservableCollection<ComplexType> Objects
    {
        get;
        private set;
    }
}

任何帮助都将不胜感激！