App.js

import React, { Component } from 'react';
import { Platform, StatusBar, StyleSheet, View } from 'react-native';
import { AppLoading, Asset, Font, Icon } from 'expo';
import { createStackNavigator } from 'react-navigation';
import {DefaultTheme, Provider as PaperProvider} from 'react-native-paper';

import HomeScreen from './screens/HomeScreen';
import StepGoalScreen from './screens/StepGoalScreen';
import CreateExerciseScreen from './screens/CreateExerciseScreen';
import GraphingScreen from './screens/GraphingScreen';
import CreateSessionScreen from './screens/CreateSessionScreen';

const theme = {
    ...DefaultTheme,
    dark: true,
    roundness: 2,
    colors: {
        ...DefaultTheme.colors,
        primary: '#5c92aa',
        accent: '#5c92aa',
        background: '#ecf8ff',
        surface: '#30375e',
        text: '#041234',
        disabled: '#8dc2dc',
        placeholder: '#5c618b',
        backdrop: '#ffffff',
    },
    fonts: {
        ...DefaultTheme.fonts,

    }
};

export default class App extends Component {
    constructor(props) {
        super(props);
        this.state = {
            isLoadingComplete: false,
        }
    }

    _loadResourcesAsync = async () => {
        return Promise.all([
            Asset.loadAsync([
                require('./assets/images/robot-dev.png'),
                require('./assets/images/robot-prod.png'),
            ]),
            Font.loadAsync({
                // This is the font that we are using for our tab bar
                ...Icon.Ionicons.font,
                // We include SpaceMono because we use it in HomeScreen.js. Feel free
                // to remove this if you are not using it in your app
                'space-mono': require('./assets/fonts/SpaceMono-Regular.ttf'),
            }),
        ]);
    };

    _handleLoadingError = error => {
        // In this case, you might want to report the error to your error
        // reporting service, for example Sentry
        console.warn(error);
    };

    _handleFinishLoading = () => {
        this.setState({ isLoadingComplete: true });
    };

    render() {
        if (!this.state.isLoadingComplete && !this.props.skipLoadingScreen) {
            return (
                <AppLoading
                    startAsync={this._loadResourcesAsync}
                    onError={this._handleLoadingError}
                    onFinish={this._handleFinishLoading}
                />);
        } else {
            return(
                <PaperProvider theme={theme}>
                    <RootStack />
                </PaperProvider>
            );
        }
    }
}

const RootStack = createStackNavigator({
        Home: HomeScreen,
        StepGoal: StepGoalScreen,
        CreateExercise: CreateExerciseScreen,
        ExerciseGraph: GraphingScreen,
        CreateSession: CreateSessionScreen,
    },
    {
        initialRouteName: 'Home',
    });