Vaadin UI类不会添加组件

Question

I was hoping you could help me figure out why my UI class isn't adding components.

What I was hoping for was a bar along the top with 4 buttons each with a link. However, when I load a page, nothing shows. A blue bar flashes at the top but this quickly fades(I think it's some kind of load bar). Does anyone have the missing puzzle piece?

MyUI.java

package org.vaadin.spring.tutorial;

import com.vaadin.annotations.Theme;
import com.vaadin.navigator.Navigator;
import com.vaadin.navigator.View;
import com.vaadin.navigator.ViewDisplay;
import com.vaadin.server.VaadinRequest;
import com.vaadin.spring.annotation.SpringUI;
import com.vaadin.spring.annotation.SpringViewDisplay;
import com.vaadin.ui.*;
import com.vaadin.ui.themes.ValoTheme;
import org.vaadin.spring.tutorial.views.DefaultView;
import org.vaadin.spring.tutorial.views.LoginView;
import org.vaadin.spring.tutorial.views.UIScopedView;
import org.vaadin.spring.tutorial.views.ViewScopedView;

import javax.swing.text.html.CSS;

@Theme("valo")
@SpringUI
@SpringViewDisplay
public class MyUI extends UI {
    @Override
    protected void init(VaadinRequest request) {
        final VerticalLayout myWindow = new VerticalLayout();
        myWindow.setSizeFull();
        setContent(myWindow);

        final CssLayout topBar = new CssLayout();

        for (String[] s: new String[][]{{"UI","ui"}, {"View","view"}, {"","Home"}, {"Login","login"}}) {
            topBar.addComponent(this.createNavigationButton(s[0], s[1]));
        }

        myWindow.addComponent(topBar);
    }

    private Button createNavigationButton(String caption,
                                          final String viewName) {
        Button button = new Button(caption);
        button.addStyleName(ValoTheme.BUTTON_SMALL);
        // If you didn't choose Java 8 when creating the project, convert this
        // to an anonymous listener class
        button.addClickListener(
                event -> getUI().getNavigator().navigateTo(viewName));
        return button;
    }

}

Answer 1

The answer is I was missing a way to send the view through to the page. To fix this, I did the following:

1, I moved this from the method to the class as a field:

final VerticalLayout myWindow = new VerticalLayout();

2, I made the class MyUI extend UI but also implement ViewDisplay, like this:

public class MyUI extends UI implements ViewDisplay {}

3, I added the showView method, as required by the ViewDisplay class. The single line in there is necessary to the functionality, as far as I can tell:

public void showView(View view) {
    MY_WINDOW.addComponent((Component) view);
}

Once these things are done, it should be working.

Answer 2

To use navigateTo do you need initialize the Navitator class on the UI. This is the missing puzzle piece. getNavigator() return that instance. Check the Vaadin reference: https://vaadin.com/docs/-/part/framework/advanced/advanced-navigator.html