navigation.js

import React from 'react'
import { NavigationContainer } from '@react-navigation/native'
import {createStackNavigator } from '@react-navigation/stack'
import HomeScreen from './Screens/HomeScreen'
import NewPostScreen from './Screens/NewPostScreen'
import LoginScreen from './Screens/LoginScreen'
import SignupScreen from './Screens/SignupScreen'

const Stack = createStackNavigator()

const screenOptions = {
    headerShown: false,
}

export const SignedInStack = () => (
    <NavigationContainer>
        <Stack.Navigator 
            initialRouteName='HomeScreen' 
            screenOptions={screenOptions} 
        >
            <Stack.Screen name='HomeScreen' component={HomeScreen} />
            <Stack.Screen name='NewPostScreen' component={NewPostScreen} />
        </Stack.Navigator>
    </NavigationContainer>
)

export const SignedOutStack = () => (
    <NavigationContainer>
        <Stack.Navigator 
            initialRouteName='LoginScreen' 
            screenOptions={screenOptions} 
        >
            <Stack.Screen name='LoginScreen' component={LoginScreen} />
            <Stack.Screen name='SignupScreen' component={SignupScreen} />
        </Stack.Navigator>
    </NavigationContainer>
)