App.js

import React from 'react'
import { Platform, StatusBar, StyleSheet, View, BackHandler } from 'react-native'
import { AppLoading, Asset, Font, Icon } from 'expo'
import AppNavigator from './navigation/AppNavigator'

export default class App extends React.Component {
  state = {
    isLoadingComplete: false,
  }

  componentWillMount() {
    BackHandler.addEventListener('hardwareBackPress', this.onBackButton)
  }

  componentWillUnmount() {
    BackHandler.removeEventListener('hardwareBackPress', this.onBackButton)
  }

  onBackButton = () => {
    if (this.props.navigation && this.props.navigation.goBack) {
      this.props.navigation.goBack(null)
      return true
    }
    return false
  }

  render() {
    if (!this.state.isLoadingComplete && !this.props.skipLoadingScreen) {
      return (
        <AppLoading
          startAsync={this._loadResourcesAsync}
          onError={this._handleLoadingError}
          onFinish={this._handleFinishLoading}
        />
      )
    } else {
      return (
        <View style={s.container}>
          {Platform.OS === 'ios' && <StatusBar barStyle="default" />}
          {Platform.OS === 'android' && <View style={s.viewStatusBarSpace} />}
          <AppNavigator />
        </View>
      )
    }
  }

  _loadResourcesAsync = async () => {
    return Promise.all([
      Asset.loadAsync([

      ]),
      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 })
  }
}

const s = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
  },
  viewStatusBarSpace: {
    height: StatusBar.currentHeight,
    // backgroundColor: 'red'
  }
})