title: react-native flatlist which has extraData props can`t re-render
body: <p>this is offical example,I write it to my project.
  however, there is a problem:flatlist item can`t re-render when state Changed.</p>
  
  <p>this is my code;</p>
  
  <pre><code>_renderItem = ((item) =&gt; (
      &lt;SelectListItem
          id = { item.item.id }
          onPressItem = { this._onPressItem }
          selected = { this.state.selected.get(item.id) }
          title = { item.item.title }
          /&gt;
      )
  );
  
  render(){
      return(
              &lt;FlatList
                  data = {this._dataArray}
                  extraData = { this.state }
                  keyExtractor = {this._keyExtractor}
                  renderItem = { this._renderItem }
              /&gt;
      );
  }
  </code></pre>