title: Access Redux state using React Navigation
body: <p>I have the following Navigator using <a href="https://reactnavigation.org/" rel="noreferrer">React-Navigation</a>:</p>
  
  <pre><code>const Navigator = StackNavigator(
    {
      Home: {
        screen: Home
      },
      User: {
        screen: User
      }
    }
  )
  </code></pre>
  
  <p>And my <code>User</code> component:</p>
  
  <pre><code>export default class User extends Component {
    static navigationOptions = {
      title: () =&gt; 'User'
    }
  
    render() {
      return (
        &lt;Text&gt;This is the user page.&lt;/Text&gt;
      )
    }
  }
  </code></pre>
  
  <p>I want the title of the <code>User</code> scene's navigation bar to be the user's name. The name is kept within the Redux state.</p>
  
  <p>Since I'm accessing the <code>User</code> scene from the <code>Home</code> scene, I could pass the user's name when I push the scene:</p>
  
  <pre><code>this.props.navigation.navigate('User', {name: user.name})
  </code></pre>
  
  <p>However if the user's name is updated when on the <code>User</code>, then the navigation title will not be updated. The only solution I can see is to access the Redux state from within <code>navigationOptions</code>. Is there a way to do this or a better way to handle this issue? Thanks.</p>