Wicket-ComponentNotFoundException：组件已从页面中删除

Question

org.apache.wicket.core.request.handler.ComponentNotFoundException:
Component 'navbar:navbarAvatar:navAvatarPanel:4:navAvatarArea:menuPanel:menuItem:menuLink' has been removed from page.

下面是我的代码：

navbarpanel.java

public class NavBarPanel extends Panel {
    public NavBarPanel(String id) {
        super(id);
        /* ... */

        WebMarkupContainer navBarAvatar = new WebMarkupContainer(NavbarAvatar$wicketId) {
            private static final long serialVersionUID = -2447768280463773678L;

            @Override
            public boolean isVisible() {
                return session.isSignedIn();
            }
        };

        List<Panel> avatarMenuItems = new ArrayList<Panel>();
        avatarMenuItems.add(new MenuLink(Logout$wicketId, "Logout", WelcomeWebPage.class, menuModel));
        /* adding additional links at this point ... */

        navBarAvatar.add(new ListView<Panel>("navAvatarPanel", avatarMenuItems) {
            private static final long serialVersionUID = 1L;

            @Override
            protected void populateItem(ListItem<Panel> item) {
                final Panel panel = item.getModelObject();
                item.add(new MenuFragment(panel, "navAvatarArea"));
            }
        });

        this.add(navBarAvatar);
    }
}

public class MenuFragment extends Fragment {
    private static final long serialVersionUID = 5735397386662232792L;

    public MenuFragment(Panel panel, String area) {
        super(area, "menuFragment", NavBarPanel.this);

        add(panel);
    }
}

navbarpanel.html

<wicket:panel>
    <!-- ... -->
    <div wicket:id="navbarAvatar" class="navbar-avatar">
        <ul>
            <wicket:container wicket:id="navAvatarPanel">
                <wicket:container wicket:id="navAvatarArea"/>
            </wicket:container>
        </ul>
    </div>
    <!-- ... -->
    <wicket:fragment wicket:id="menuFragment">
        <wicket:container wicket:id="menuPanel"></wicket:container>
    </wicket:fragment>
</wicket:panel>

public MenuLink(String markupId, String label, Class<? extends Page> page, MenuModel model) {
    super("menuPanel");
    this.markupId = markupId;
    this.page = page;
    this.model = model;
    this.initComponentTree(label);
}

private void initComponentTree(final String label) {
    WebMarkupContainer menuItem = new WebMarkupContainer("menuItem");

    Link<Void> menuLink = new Link<Void>("menuLink") {
        private static final long serialVersionUID = 1L;

        @Override
        public void onClick() {
            MenuLink.this.menuOnClick(label);
        }
    };

    menuLink.add(new Label("menuLabel", label));
    menuLink.setMarkupId(this.markupId);

    menuItem.add(menuLink);

    this.add(menuItem);
}

<wicket:panel>
    <li wicket:id="menuItem">
        <a wicket:id="menuLink">
            <span wicket:id="menuLabel">[label]</span>
        </a>
    </li>
</wicket:panel>

Answer 1

我的猜测是http会话已经过期，找不到菜单项，因为isvisible=session.issignedin（）；导致整个菜单不存在。

如果是这种情况，那么应该改进Wicket，以提供更好的异常消息，告诉确切找不到哪个组件，而不是请求的组件路径。

附言。建议使用onconfigure（）{setVisible（...）}而不是重写isvisible（），因为后者在呈现过程中会被多次调用，可能会更慢。