title: Vaadin data model doesn' t update
body: <p>I'm trying to develop my first application in vaadin. I saw a little of components, layout ..... and now i'm trying to learn how bind the UI component with the DataModel.</p>
  
  <p>I have this class</p>
  
  <pre><code>public class Utente {
  
  private String nome = "Mario";
  private String cognome = "Rossi";
  
  
  public Utente() {
      // TODO Auto-generated constructor stub
  }
  
  public String getNome() {
      return nome;
  }
  
  public void setNome(String nome) {
      this.nome = nome;
  }
  
  public String getCognome() {
      return cognome;
  }
  
  public void setCognome(String cognome) {
      this.cognome = cognome;
  }
  
  }
  </code></pre>
  
  <p>and this CustomComponent</p>
  
  <pre><code>public class MyRegistration extends CustomComponent {
  
  private FormLayout mainLayout;
  private Button buttonSalva;
  private Utente utente;
  private BeanItem&lt;Utente&gt; beanItem;
  private FieldGroup fieldGroup;
  
  public MyRegistration() {
      buildMainLayout();
      setCompositionRoot(mainLayout);
  }
  
  private FormLayout buildMainLayout() {
  
      utente = new Utente();
      beanItem = new BeanItem&lt;Utente&gt;(utente);
      fieldGroup = new FieldGroup(beanItem);
      mainLayout = new FormLayout();
  
      setWidth("100.0%");
      setHeight("100.0%");
  
      mainLayout.addComponent(fieldGroup.buildAndBind("Nome", "nome"));
      mainLayout.addComponent(fieldGroup.buildAndBind("Cognome", "cognome"));
  
      // buttonSalva
      buttonSalva = new Button();
      buttonSalva.setCaption("Salva");
      mainLayout.addComponent(buttonSalva);
  
      addListener();
  
      return mainLayout;
  }
  
  private void addListener(){
  
      buttonSalva.addClickListener(new Button.ClickListener() {
          public void buttonClick(ClickEvent event) {
              System.out.println(fieldGroup.getItemDataSource());
          }
      });
  }
  
  }
  </code></pre>
  
  <p>my trouble is that if I press the button, i show always Mario Rossi also if i modify the content of the fields.</p>
  
  <p>Where i wrong?</p>