title: How to hide the tabBar in the child screen of a StackNavigator
body: <p>I declare two screens A and B in a StackNavigator. The StackNavigator is nested in a tabNavigator. The bar is visible for the both screens. And i want to show it just in the screen A. I set the tabBarVisible to false in the screen B but no effects.</p>
  
  
  
  <pre class="lang-js prettyprint-override"><code>import React,{Component} from 'react'; 
  import {Text} from 'react-native'; 
  
  import {StackNavigator, TabNavigator} from 'react-navigation'; 
  
  
  
  class ScreenA extends Component {
   static navigationOptions = {
      title: 'A'
   }
  
   render(){
      &lt;Text&gt;ScreenA&lt;/Text&gt;
   }
  }
  
  class ScreenB extends Component {
   static navigationOptions = {
      title: 'B'
   }
  
   render(){
      &lt;Text&gt;ScreenB&lt;/Text&gt;
   }
  }
  
  const HomeScreen = new StackNavigator({
   A : {screen : ScreenA}, 
   B : {Screen : ScreenB}
  }); 
  
  const TabBar = new TabNavigator({
   Main : {screen : HomeScreen}
  }); 
  
  export default TabBar;
  </code></pre>