I have three file ( The full project is https://github.com/EnginYilmaz/kpbduser)
I want to print a Map on FetchData and on marker click want to pass which markerkey pressed to MapScreen.js and then Query the people on index key and show data with ShowData.js but I don't know how to pass data back from FetchData.js to Parent (MapScreen.js). I illustrated my question on 
You can use props to handle data passing in react native. A basic example is shown below
export default class ParentClass extends Component { callbackMethod = (value) => { console.log('Callback is called',value); }; render() { return <ChildView callbackMethod={this.callbackMethod} />; } } export default class ChildView extends Component { onPress=()=>{ this.props.callbackMethod("Hello"); } render() { return <Button onPress={this.onPress} />; } } 