I'm trying to create a simple toolbar in WPF, but the toolbar shows up with no corresponding buttons on it, just a very thin blank white strip. Any idea what I'm doing wrong, or what the recommended procedure is? Relevant code fragments so far:

        var tb = new ToolBar();

        var b = new Button();
        b.Command = comback;
        Image myImage = new Image();
        myImage.Source = new BitmapImage(new Uri("back.png", UriKind.Relative));
        b.Content = myImage;
        tb.Items.Add(b);

        var p = new DockPanel();
        //DockPanel.SetDock(mainmenu, Dock.Top);
        DockPanel.SetDock(tb, Dock.Top);
        DockPanel.SetDock(sb, Dock.Bottom);
        //p.Children.Add(mainmenu);
        p.Children.Add(tb);
        p.Children.Add(sb);
        Content = p;