text: import {NavigationActions} from 'react-navigation';
  
  let _navigator;
  
  function setTopLevelNavigator(navigatorRef) {
    _navigator = navigatorRef;
  }
  
  function navigate(routeName, params) {
    _navigator.dispatch(
      NavigationActions.navigate({
        routeName,
        params,
      })
    );
  }
  
  // add other navigation functions that you need and export them
  
  export default {
    navigate,
    setTopLevelNavigator,
  };
  