text: import React from 'react';
  import { View, Text, StyleSheet, StatusBar, AsyncStorage } from 'react-native';
  import Touchable from 'react-native-platform-touchable';
  
  export default function LoginScreen(props) {
    const onSignIn = async () => {
      await AsyncStorage.setItem('userToken', 'abc');
      props.navigation.navigate('App')
    };
    return (
      <View style={styles.container}>
        <StatusBar barStyle="dark-content" />
        <Text style={styles.optionsTitleText}>
          Login Page
        </Text>
        <Touchable onPress={() => { onSignIn() }}>
          <Text>Login</Text>
        </Touchable>
      </View>
    );
  }
  
  LoginScreen.navigationOptions = {
    header: null,
  };
  
  const styles = StyleSheet.create({
    container: {
      flex: 1,
      backgroundColor: '#fff',
    },
    optionsTitleText: {
      fontSize: 16,
      marginLeft: 15,
      marginTop: 24,
      marginBottom: 12,
    },
  });
  