我正在使用MahApps Metro UI工具包编写WPF应用程序。
http://mahapps.com/guides/quick-start.html
从他们网站上的指南来看，我基本上已经完成了我的申请，看起来很光滑。唯一的问题，我有是我还没有能够找出如何使用图标包，他们提供的上下文菜单图标。

这里有一个我正在尝试的视觉例子。虽然我能够让原来的“Windows”菜单项显示它的图标，但我无法为contextmenu menuitems做同样的事情。是我做错了什么，还是有办法解决这个问题？
下面是我的.xaml：

<Menu IsMainMenu="True">
    <MenuItem Header="_Windows" ContextMenuService.IsEnabled="False" Click="WindowsMenuItem_Click">
        <MenuItem.Icon>
            <Rectangle Width="15" Height="15" Fill="{Binding RelativeSource={RelativeSource AncestorType=MenuItem}, Path=Foreground}">
                <Rectangle.OpacityMask>
                    <VisualBrush Stretch="Fill" Visual="{StaticResource appbar_window}" />
                </Rectangle.OpacityMask>
            </Rectangle>
        </MenuItem.Icon>
        <MenuItem.ContextMenu>
            <ContextMenu>
                <MenuItem Header="_Welcome Module">
                    <MenuItem.Icon>
                        <Rectangle Width="15" Height="15" Fill="{Binding RelativeSource={RelativeSource AncestorType=MenuItem}, Path=Foreground}">
                            <Rectangle.OpacityMask>
                                <VisualBrush Stretch="Fill" Visual="{StaticResource appbar_home}" />
                            </Rectangle.OpacityMask>
                        </Rectangle>
                    </MenuItem.Icon>
                </MenuItem>
                <MenuItem Header="_Schedule Module">
                    <MenuItem.Icon>
                        <Rectangle Width="15" Height="15" Fill="{Binding RelativeSource={RelativeSource AncestorType=MenuItem}, Path=Foreground}">
                            <Rectangle.OpacityMask>
                                <VisualBrush Stretch="Fill" Visual="{StaticResource appbar_calendar}" />
                            </Rectangle.OpacityMask>
                        </Rectangle>
                    </MenuItem.Icon>
                </MenuItem>
                <MenuItem Header="_Performance Module">
                    <MenuItem.Icon>
                        <Rectangle Width="15" Height="15" Fill="{Binding RelativeSource={RelativeSource AncestorType=MenuItem}, Path=Foreground}">
                            <Rectangle.OpacityMask>
                                <VisualBrush Stretch="Fill" Visual="{StaticResource appbar_table}" />
                            </Rectangle.OpacityMask>
                        </Rectangle>
                    </MenuItem.Icon>
                </MenuItem>
                <MenuItem Header="_Audit Module">
                    <MenuItem.Icon>
                        <Rectangle Width="15" Height="15" Fill="{Binding RelativeSource={RelativeSource AncestorType=MenuItem}, Path=Foreground}">
                            <Rectangle.OpacityMask>
                                <VisualBrush Stretch="Fill" Visual="{StaticResource appbar_graph_line}" />
                            </Rectangle.OpacityMask>
                        </Rectangle>
                    </MenuItem.Icon>
                </MenuItem>
            </ContextMenu>
        </MenuItem.ContextMenu>
    </MenuItem>
</Menu>

和我的.xaml.cs：

public partial class MainWindow
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = new MainWindowViewModel();
    }

    private void WindowsMenuItem_Click(object sender, RoutedEventArgs e)
    {
        (sender as MenuItem).ContextMenu.IsEnabled = true;
        (sender as MenuItem).ContextMenu.PlacementTarget = (sender as MenuItem);
        (sender as MenuItem).ContextMenu.Placement = System.Windows.Controls.Primitives.PlacementMode.Bottom;
        (sender as MenuItem).ContextMenu.IsOpen = true;
    }
}