问com.vaadin.shared.ui.button.ButtonServerRpc中无法调用方法单击

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package com.eduwallchart.schulung2;

import javax.servlet.annotation.WebServlet;

import com.vaadin.annotations.Theme;
import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.server.VaadinRequest;
import com.vaadin.server.VaadinServlet;
import com.vaadin.ui.Button;
import com.vaadin.ui.Button.ClickEvent;
import com.vaadin.ui.Label;
import com.vaadin.ui.TextField;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;

@Theme("mytheme")
@SuppressWarnings("serial")
public class MyVaadinUI extends UI {

    @WebServlet(value = "/*", asyncSupported = true)
    @VaadinServletConfiguration(productionMode = false, ui = MyVaadinUI.class, widgetset = "com.eduwallchart.schulung2.AppWidgetSet")
    public static class Servlet extends VaadinServlet {
    }

    @Override
    protected void init(VaadinRequest request) {
        final VerticalLayout layout = new VerticalLayout();
        layout.setMargin(true);
        setContent(layout);

        Button button = new Button("Convert Float to Int");
        final TextField textfield = new TextField("Int-Wert:");
        Label label = new Label("0.0");
        button.addClickListener(new Button.ClickListener() {

            public void buttonClick(ClickEvent event) {
                float floatValue;
                String intValue;
                floatValue = (Float) textfield.getData();
                intValue = String.valueOf(floatValue);
                textfield.setCaption(intValue);
            }
        });

        layout.addComponent(textfield);
        layout.addComponent(button);

    }

}