title: react-navigation: Is it possible to pass a callback to children (e.g.changeHandler)?
body: <p>What I've been trying is to <strong>pass a callback into a screen</strong>.</p>
  
  <p>Here is an excerpt of my experimentation...</p>
  
  <pre><code>export default class Test extends React.Component {
      constructor(props) {
          super(props);
      };
  
      handleOnPress(data){
      //How do we pass this callback to "Home" or "Sub"?
      }
  
      render() {
          const Navigator = StackNavigator({
              Home: {screen: Home},
              Sub:  {screen: Sub}
          });
          let data = {blah:"blah blah"};
  
          return (&lt;Navigator screenProps={data} /&gt;);
      }
  }
  </code></pre>
  
  <p>In this example, I can get <code>this.props.screenProps.blah</code> in both <code>Home</code> and <code>Sub</code>.
  I assumed that being able to pass a prop would mean being able to pass a call back too, but I feel like I wasn't right.</p>
  
  <p>Has anyone encountered this issue?</p>
  
  <p>Any advice will be appreciated.</p>