Mobx with functional component

LoginScreen.js

import React from 'react';
import { Button, Text, SafeAreaView } from 'react-native';
import { observable } from 'mobx';
import { observer } from 'mobx-react';

const store = observable({ count: 0 });

const LoginScreen = observer(() => {
  handleInc = () => store.count++;
  handleDesc = () => store.count--;
  return (
    <SafeAreaView>
      <Button title="+" onPress={handleInc} />
      <Button title="-" onPress={handleDesc} />
      <Text style={{ alignSelf: 'center' }}>{store.count}</Text>
    </SafeAreaView>
  )
});

export default LoginScreen;