title: react native this.refs.nav is not defined
body: <p>new to react native, trying to render the main page with a button on the navigation to go the user page.</p>
  
  <pre><code>var TourChampIOs = React.createClass({
  
      getInitialState() {
         ....
      },
  
      componentWillMount() {
  
          ....
      },
  
      _handleUserDataPress: function() {
  
          // Get by ref not prop
          this.refs.nav.push({
              component: UserPage,
              title: 'User Page'
          });
      },    
     render: function() {
  
                  return &lt;NavigatorIOS
                      style={styles.container}
                      initialRoute={{
                          title: 'Tour Champ',
                          component: ThemeList,
                          rightButtonTitle: tc.user.displayName.split(' ')[0],
                          onRightButtonPress: this._handleUserDataPress
                      }}/&gt;;
  
          }
  </code></pre>
  
  <p>the error i'm getting is 
  <code>Error: Cannot read property 'push' of undefined</code></p>