title: GWT MVP updating Activity state on Place change
body: <p>What is the best practise to update Activity state on Place change? Imagine you have an activity with view that displays list of categories and list of items in the category. If different category is selected then app goes to new place with category ID. I want then to only refresh items and not to create new activity that also re-reads category list.</p>
  
  <p>My current approach is like this:
  </p>
  
  <pre><code>public class AppActivityMapper implements ActivityMapper {
  
      private ItemListActivity itemListActivity;
  
      ...
  
      public Activity getActivity(final Place place) {
          final Activity activity;
  
          if (place instanceof ItemListPlace) {
              if (itemListActivity == null) {
                  itemListActivity = new ItemListActivity((ItemListPlace) place, clientFactory);
              } else {
                  itemListActivity.refresh((ItemListPlace) place);
              }
              activity = itemListActivity;
          } else {
              itemListActivity = null;
          }
  
          ...
          return activity;
      }
  
      ...
  </code></pre>