当泛型类型未知时,将对象强制转换为泛型类

在Silverlight项目中,我定义了以下类。

public class ThemeResource<T>
{
    public string Name { get; set; }
    public string Description { get; set; }
    public Type Type { get { return typeof(T); } }
    public string TypeName { get { return Type.FullName; } }
    public T Resource { get { return (T)Application.Current.Resources[this.Name]; } }
}

在我的代码后面有几个列表在使用这个类。

public List<ThemeResource<SolidColorBrush>> BrushResources { get; set; }
public List<ThemeResource<Color>> ColorResources { get; set; }
public List<ThemeResource<FontFamily>> FontNameResources { get; set; }
public List<ThemeResource<Thickness>> ThicknessResources { get; set; }
public List<ThemeResource<Double>> FontSizeResources { get; set; }
public List<ThemeResource<Style>> TextStyleResources { get; set; }

<UserControl x:Name="ThemeResourcesPage" ...>
    <ListBox Style="{StaticResource BrushResourceListBoxStyle}"
                ItemsSource="{Binding ElementName=ThemeResourcesPage, Path=BrushResources}"
                SelectionChanged="ListBox_SelectionChanged" />
</UserControl>

这行不通:

private void ListBox_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
{
    if (e.AddedItems.Count != 1)
        return;

    var tr = (ThemeResource<T>)e.AddedItems[0];
    var msg = string.Format("Name: {0}\nType: {1}\nDescription: {2}",
                            tr.Name, tr.TypeName, tr.Description);
    MessageBox.Show(msg);
}

如何在不知道T是什么的情况下将对象投射到资源?