screens.js

import React from 'react';
import { StyleSheet, Text, View } from 'react-native';

const Screen1 = () => (<View style={styles.container}><Text>Screen 1</Text></View>)
const Screen2 = () => (<View style={styles.container}><Text>Screen 2</Text></View>)
const Screen3 = () => (<View style={styles.container}><Text>Screen 3</Text></View>)

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
});