我有一个自定义控件，我疯了，为主机的名称，和图标的面板，并作出触发器，所以它会改变颜色时，我悬停图标或选择它

public class NavButton : ListBoxItem {
    static NavButton() {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(NavButton),
            new FrameworkPropertyMetadata(typeof(NavButton)));
    }

    public Uri NavLink {
        get { return (Uri)GetValue(NavLinkProperty); }
        set { SetValue(NavLinkProperty, value); }
    }

    // This property will hold specifics on where to navigate within our appreciation
    public static readonly DependencyProperty NavLinkProperty =
        DependencyProperty.Register(
            "NavLink", typeof(Uri),
            typeof(NavButton),
            new PropertyMetadata(null));

    // This property will hold specifics on the icon
    public Label Icon {
        get { return (Label)GetValue(IconProperty); }
        set { SetValue(IconProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Icon.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty IconProperty =
        DependencyProperty.Register("Icon",
            typeof(Label),
            typeof(NavButton),
            new PropertyMetadata(null));

问题是，每当我在main中调用此控件时，总是会得到此错误

我是这么叫的

<custom:NavButton
                Padding="6"
                FontFamily="{StaticResource Material}"
                Icon="{x:Static fonts:IconFont.VolumeHigh}"/>

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