title: Using EXT-GWT ComboBox
body: <p>I extend <code>ComboBox</code> and in constructor have such code:</p>
  
  <pre><code>ModelType type = new ModelType();  
  type.setRoot("data");
  type.addField("id", "id");
  type.addField("name", "name");
  
  JsonLoadResultReader&lt;ListLoadResult&lt;ModelData&gt;&gt; reader = new JsonLoadResultReader&lt;ListLoadResult&lt;ModelData&gt;&gt;(type);
  
  RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, "/category/getall");
  HttpProxy&lt;String&gt; proxy = new HttpProxy&lt;String&gt;(builder);
  
  BaseListLoader&lt;ListLoadResult&lt;ModelData&gt;&gt; loader = new BaseListLoader&lt;ListLoadResult&lt;ModelData&gt;&gt;(proxy, reader);
  
  ListStore&lt;ModelData&gt; store = new ListStore&lt;ModelData&gt;(loader);
  
  
  setStore(store);
  loader.load();
  setValueField("id");
  setDisplayField("name");
  setName("categoty");
  </code></pre>
  
  <p>Result: ajax query send to server but no results see in combobox but when click on it it loads data again and then display it, and how to set value to combobox?</p>