导航器与vaadin空指针异常

Question

我是vaadin的新手，我正在构建一个需要使用多个视图的应用， 这里是代码片段和堆栈跟踪， 我检查了构建路径，以确保它不是一个依赖问题，谷歌搜索没有给出有用的答案或线索

Button button = new Button("Login", new Button.ClickListener(){
            @Override
            public void buttonClick(ClickEvent event){
            layout.addComponent(new Label("establishing connection ..."));
            getUI().getNavigator().navigateTo("");
            }

        });
@Override
    public void enter(ViewChangeEvent event) {
        // TODO Auto-generated method stub

    }
}

这是导航器类：

public class navigator extends LoInf {
    Navigator navigator;
    public static final String MAINVIEW = "main";
    //public static final String view = "interface";

    @Override
    protected void init(VaadinRequest request) {
        getPage().setTitle("login");


        navigator = new Navigator(this,this);


        navigator.addView(MAINVIEW, new LoInf());
        navigator.addView("", RMQcl.class);
    }

    public static void navigateTo(String mainview2) {


    }

}

这是堆栈跟踪

oct. 24, 2017 3:05:30 PM com.vaadin.server.DefaultErrorHandler doDefault
GRAVE: 
java.lang.NullPointerException
    at my.vaadin.Project.LoInf$1.buttonClick(LoInf.java:43)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:510)
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:211)
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:174)
    at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1033)
    at com.vaadin.ui.Button.fireClick(Button.java:370)
    at com.vaadin.ui.Button$1.click(Button.java:57)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155)
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:116)
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocation(ServerRpcHandler.java:445)
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:410)
    at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:274)
    at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:90)
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1568)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:381)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:845)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1689)
    at org.eclipse.jetty.websocket.server.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:225)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1676)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:581)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1174)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:511)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1106)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:213)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:119)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134)
    at org.eclipse.jetty.server.Server.handle(Server.java:524)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:319)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:253)
    at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)
    at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95)
    at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.executeProduceConsume(ExecuteProduceConsume.java:303)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceConsume(ExecuteProduceConsume.java:148)
    at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:136)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:671)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:589)
    at java.lang.Thread.run(Thread.java:745)

似乎无法弄清问题是什么， 帮助赞赏

[更新] 这是我试图导航到的课程：

@SpringUI
public class RMQcl extends RMQ implements UserRep,View{
    UserRep repo;
    Grid <UserModel> grid;
    TextField filter = new TextField();
    UserEdit editor;
    Button addnew;  
    UserModel User;
    Binder<UserModel> binder = new Binder<>(UserModel.class);
    final VerticalLayout layout = new VerticalLayout(filter,grid);
    @Autowired
    public RMQcl(UserRep repo,UserEdit editor){
        this.repo = repo;
        this.grid = new Grid<>(UserModel.class);
        this.editor = editor;
        this.filter = new TextField();
        binder.bindInstanceFields(this);
        this.addnew = new Button("New User",FontAwesome.PLUS);

        logout = new Button("Logout");
        logout.addClickListener(new ClickListener() {
        private static final long serialVersionUID = 1L;
                public void buttonClick(ClickEvent event) {
                     getUI().getNavigator().navigateTo(navigator.MAINVIEW);


            }

    });


}
    //@Override
    public void init(VaadinRequest request){
        layout.addComponents(grid);
        setContent(layout);
        listUsers(null);
        binder.setBean(User);
        HorizontalLayout actions = new HorizontalLayout(filter,addnew);
        VerticalLayout Layout = new VerticalLayout(actions,grid,editor);
        setContent(Layout);

        grid.setHeight(300,Unit.PIXELS);
        grid.setColumns("id","firsname","lastname");
        filter.setPlaceholder("Filtering by lastname");

        filter.setValueChangeMode(ValueChangeMode.LAZY);
        filter.addValueChangeListener(e->listUsers(e.getValue()));


        grid.asSingleSelect().addValueChangeListener(e->{
            editor.editUser(e.getValue());
        });
        addnew.addClickListener(e -> editor.editUser(new UserModel("", "")));

        editor.setChangeHandler(()->{
            editor.setVisible(false);
            listUsers(filter.getValue());
        });

        listUsers(null);

    }

    private void setContent(VerticalLayout layout2) {
        // TODO Auto-generated method stub

    }
    private void listUsers(String Filter) {
        if(StringUtils.isEmpty(Filter)){
        grid.setItems(repo.findAll());
        }else{
            grid.setItems(repo.findByLastNameStartsWithIgnoreCase(Filter));
        }

        filter.setPlaceholder("Filter by last name");
        filter.setValueChangeMode(ValueChangeMode.LAZY);
        filter.addValueChangeListener(e-> listUsers(e.getValue()));
        setContent(layout);


    }