如何在WPF中使用Alt键切换主菜单可见性？

>当应用程序启动时,它不可见
>按下并释放Alt使其可见
>再次按下并释放Alt会使其再次隐身
>重复直到无聊

我怎样才能做到这一点？它必须是代码吗？

添加回复提交的答案,因为我仍然遇到麻烦：

我的Shell代码隐藏现在看起来像这样：

public partial class Shell : Window
{
    public static readonly DependencyProperty IsMainMenuVisibleProperty;

    static Shell()
    {
        FrameworkPropertyMetadata metadata = new FrameworkPropertyMetadata();
        metadata.DefaultValue = false;

        IsMainMenuVisibleProperty = DependencyProperty.Register(
            "IsMainMenuVisible",typeof(bool),typeof(Shell),metadata);
    }

    public Shell()
    {
        InitializeComponent();

        this.PreviewKeyUp += new KeyEventHandler(Shell_PreviewKeyUp);
    }

    void Shell_PreviewKeyUp(object sender,KeyEventArgs e)
    {
        if (e.SystemKey == Key.LeftAlt || e.SystemKey == Key.RightAlt)
        {
            if (IsMainMenuVisible == true)
                IsMainMenuVisible = false;
            else
                IsMainMenuVisible = true;
        }
    }

    public bool IsMainMenuVisible
    {
        get { return (bool)GetValue(IsMainMenuVisibleProperty); }
        set { SetValue(IsMainMenuVisibleProperty,value); }
    }
}