title: React Native: passing data between screens
body: <p>I'm trying to create a small app, but have many questions)
  I have 3 screen and use react-navigation to pass data. the scheme is following:</p>
  
  <pre><code>1) loading screen (fetch data and save it to AsyncStorage+handling data and save to obj1 for pickers)
  (pass obj1)
  2)main screen (get data,render pickers based on it, take selected values and pass them next)
  (pass pickers selection+input)
  3)some results(get data from Asyncstorage, some calculating and render results)
  </code></pre>
  
  <p>so I have two questions. </p>
  
  <p>when I navigate back from 3) to 2) I have an error that screen2 need data, which was passed from screen1. yes - i've checked if this data pass to 3 and then to 2 when Back Button is pressed, and there is no error, but I'm sure this is bad solution</p>
  
  <p>and  second..trying to explain) on screen 3 some calculations made on pickers selection, so it hasn't problem. but rest of them needed get data from AsyncStorage and then convert it according to Picker values and render to ListView. Despite I'm putting getting from AS on componentWillMount it's still take much time so data for rendering is undefined. Of course I'm using states, but I think this is a bad logic of data handling..</p>
  
  <p>UPD
  so I'm trying pass data from child(screen) to parent(index.ios.js), where it define as first loading view( I'm using navigator's stack screens)</p>
  
  <pre><code>export default class App extends Component {
    constructor(props) {
        super(props);
  
        };
    }
    myCallback(dataFromChild) {
        console.log("yeah", dataFromChild);
  
    }
  
    render() {
      return (
        &lt;LoadingScreen callbackFromParent={this.myCallback}/&gt;
      );
    }
  }
  </code></pre>
  
  <p>and LoadingScreen.js:</p>
  
  <pre><code>render() {
      return(
          &lt;View style={{flex: 1, backgroundColor: '#dc143c', marginTop:20}}&gt;
            &lt;Image
                source={require('./WhiteLogo.png')}
                style={{flex:3, height: undefined, width: undefined, marginLeft:20, marginRight:20}}
                resizeMode="contain"
                qwer={this.props.callbackFromParent('listInfo').bind(this)}
              /&gt;
            &lt;Spinner color='white' style={{flex:1}}/&gt;
          &lt;/View&gt;
     );
    }
  }
  </code></pre>
  
  <p>and I've got an error "Unhandled JS Exception: this.props.callbackFromParent is not a function" </p>