title: How to re-expand objects in vaadin TreeTable
body: <p>Im trying to re-expand objects in a TreeTable after I have reset the container datasource for the TreeTable but i doesnt work. Has anyone tried this before? Where am I going wrong?</p>
  
  <pre><code>private void setTableDataSource() {
      Set&lt;Object&gt; expandedMap = new HashSet&lt;Object&gt;();
      if(table.getItemIds() != null &amp;&amp; !table.getItemIds().isEmpty()){
          for(Object o : table.getItemIds()){         
              if(table.isCollapsed(o))
                  expandedMap.add(o);
          }
      }       
      table.setContainerDataSource(ContactContainerFactory.createContainer(model.getParentModel()));
      table.setVisibleColumns(new String[]{"title", "operation", "id", "price"});
      table.setColumnHeaders(getTranslatedTableHeaders());        
      if(!expandedMap.isEmpty()){
          for(Object o : expandedMap){                
              table.setCollapsed(o, false);
          }
      }
  }
  </code></pre>