如何在WPF中从DocumentViewer更改默认菜单项（如整页，适合宽度等）

Question

我有这个正在运行的DocumentViewer，

Xaml代码：

<DocumentViewer Document="{Binding XpsDocument}" Loaded="documentViewer_Initialized"/>

ViewModel代码：

void Load()
{
    MemoryStream ms = new MemoryStream();
    Package pkg = Package.Open(ms, FileMode.Create, FileAccess.ReadWrite);
    string pack = "pack://report.xps";
    PackageStore.RemovePackage(new Uri(pack));
    PackageStore.AddPackage(new Uri(pack), pkg);
    XpsDocument doc = new XpsDocument(pkg, CompressionOption.NotCompressed, pack);
    XpsSerializationManager rsm = new XpsSerializationManager(new XpsPackagingPolicy(doc), false);
    DocumentPaginator paginator = ((IDocumentPaginatorSource)CreateFlowDocument()).DocumentPaginator;
    ReportPaginator rp = new ReportPaginator(this, data);
    rsm.SaveAsXaml(rp);

    xpsDocument = doc.GetFixedDocumentSequence();
}

问题

我想在菜单栏中添加一些按钮。我找到了一个解决方案，使它工作，但它似乎不是一个可靠的方法。

我试过了：

我设法找到一个类型为ToolBar且Count为10的子项，这是默认工具栏。但我对我的做法并不满意。有没有人有更好的主意？

private void documentViewer_Initialized(object sender, EventArgs e)
{
    var dv = sender as DocumentViewer;
    if (dv == null)
        return;

    var tb = FindToolbar(dv);
    if (tb != null)
        tb.Items.Add(new Button { Content = "askjsdfsdf"});
}
public ToolBar FindToolbar(System.Windows.FrameworkElement root)
{
    ToolBar target = null;
    int c = System.Windows.Media.VisualTreeHelper.GetChildrenCount(root);
    for (int i = 0; i < c; i++)
    {
        var child = System.Windows.Media.VisualTreeHelper.GetChild(root, i) as System.Windows.FrameworkElement;
        if (child == null) continue;

        var menu = child as ToolBar;
        if (menu != null)
            if (menu.Items.Count == 10)
                return menu;

        target = FindToolbar(child);
        if (target != null) return target;
    }
    return target;
}