App.js

import React, { Component } from 'react';
import { View } from 'react-native';
import firebase from 'firebase';
import { LoginForm } from './components/LoginForm';
import { Header, Button, Spinner } from './components/common';

class App extends Component {
    state = { loggedIn: null };

    componentWillMount() {
        firebase.initializeApp({
            apiKey: 'nope',
            authDomain: 'nope',
            databaseURL: 'nope',
            projectId: 'nope',
            storageBucket: 'nope',
            messagingSenderId: 'nope'
    });

    firebase.auth().onAuthStateChanged((user) => {
        if (user) {
            this.setState({ loggedIn: true });
        } else {
            this.setState({ loggedIn: false });
        }
    });
}

    renderContent() {
        switch (this.state.loggedIn) {
            case true:
                return <Button>Log in</Button>;
            case false:
                return <LoginForm />;
            default:
                return <Spinner size="large" />;
        }
    }

    render() {
        return (
            <View>
                <Header headerText="Authentication" />
                {this.renderContent()}
            </View>
        );
    }
}

export default App;