title: Events defined in UiBinder not working?
body: <p>Sorry if it's a silly question , but I'm just starting learning GWT and got stuck to this problem for a long time ... .
  Here is my code :</p>
  
  <pre><code>public void onModuleLoad() {
  
      HelloWorldPanel helloWorldPanel = new HelloWorldPanel();
      RootPanel.get().add(helloWorldPanel);
      //RootPanel.getBodyElement().appendChild(helloWorldPanel.getElement());
  
      Button b = new Button();
      b.setText("button B");
      b.addClickHandler(new ClickHandler()
      {
        @Override
        public void onClick(ClickEvent arg0)
        {
          System.out.println("click B");
          Window.alert("Hello button B");
        }
      });
      RootPanel.get().add(b);
  }
  </code></pre>
  
  <p>And this is my HelloWorldPanel.java :</p>
  
  <pre><code>public class HelloWorldPanel extends Composite
  {
    interface HelloWorldUiBinder extends UiBinder&lt;Widget , HelloWorldPanel&gt; {}
  
    private static HelloWorldUiBinder uiBinder = GWT.create(HelloWorldUiBinder.class);
  
    @UiField TextBox nameTextBox;
  
    @UiField Button goButton;
  
    public HelloWorldPanel()
    {
      initWidget(uiBinder.createAndBindUi(this));
  
      nameTextBox = new TextBox();
      nameTextBox.setText("World");
  
      goButton = new Button("Go");
      goButton.addClickHandler(new ClickHandler()
      {
        @Override
        public void onClick(ClickEvent event)
        {
          System.out.println("clicked , event = " + event);
          Window.alert("Hello " + nameTextBox.getValue());
        }
      });
    }
  }
  </code></pre>
  
  <p>And HelloWorldPanel.ui.xml :</p>
  
  <pre><code>&lt;ui:UiBinder 
    xmlns:ui="urn:ui:com.google.gwt.uibinder"
    xmlns:g="urn:import:com.google.gwt.user.client.ui"&gt;
  
    &lt;g:HTMLPanel&gt;
      &lt;g:TextBox ui:field="nameTextBox" /&gt;
      &lt;g:Button  ui:field="goButton" text="Go"/&gt;
    &lt;/g:HTMLPanel&gt;
  
  &lt;/ui:UiBinder&gt;
  </code></pre>
  
  <p>It's a very basic "Composite" widget , but the TextBox and Button in HelloWorldPanel just not working. The default value ("World") is not shown , and button has no reaction , no System.out message ...</p>
  
  <p>But the Button defined in onModuleLoad() just works well , I don't know why.... Can somebody tell me where goes wrong ? Thanks a lot !</p>
  
  <p>Another question :
  What's the difference between <code>RootPanel.get().add(helloWorldPanel);</code> and <code>RootPanel.getBodyElement().appendChild(helloWorldPanel.getElement());</code> ? It seems the same result ...</p>