Workshop Expo / React Native (144)

Home Screen	Detail Screen	New Screen

Step 1 - Project setup (5)

Requirements:

Node.js
Git
Visual Studio Code
Expo CLI: npm install -g expo-cli
Emulator (or Smartphone) with the Expo-Client installed (https://docs.expo.io/get-started/installation/#requirements)
Expo-Docs: https://docs.expo.io

initialize Project (5)

create a new empty repo (without Readme.md and .gitignore file) called my-favorite-food-2021 on GitHub, copy the clone url and clone the project
cd my-favorite-food-2021
expo init . (don't forget the dot! select the blank template in managed workflow)
npm start

Step 2 - Config Expo (4)

The app.json (docs) file contains configuration options for your project.
We need to change the following ones:

name => my-favorite-food (the name of your app)
slug => my-favorite-food (the friendly URL name for publishing. For example, my-favorite-food will refer to the expo.io/@project-owner/my-favorite-food project)
icon => ./assets/logo.png (app icon - download)
splash.backgroundColor => #ff9100 (color to fill the loading screen background)
web.favicon => ./assets/logo.png (web favicon - download)

Step 3 - Styles (3)

set the backgroundColor from #fff to #ff9100
add a new style for the text. set the text color to #fff

Step 4 - Status Bar (10)

We want to set the background color of the status bar (docs) to #ff9100:

install StatusBar package expo install expo-status-bar
import package

import { StatusBar } from 'expo-status-bar';

make usage of the StatusBar Component

<StatusBar backgroundColor={'#ff9100'} translucent={true} style="light" />

On android devices the StatusBar is not correct until the expo app has been loaded. We can adjust this in the app.json file. Add the following optiosn:

"androidStatusBar": {
    "backgroundColor": "#ff9100",
    "translucent": false,
    "barStyle": "light-content"
}

Step 5 - Refactoring to ES6 arrow functions (5)

convert code in the App.js file to an ES6 arrow function

const HomeScreen = () => {
  return (
    <View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
      <Text>Home Screen</Text>
    </View>
  );
};

Step 6 - Components

create folder components

Text (5)

create file Text.js in the components folder
create a Headline component (use Text from react-native) and assign the following styles fontSize: 30, color: 'black'
create a Paragraph component (use Text from react-native) and assign the following styles fontSize: 16, color: 'black'
keep in mind to handle passed props (props.children => text to show in this case)
export components (multiple exports)
use both components in App.js

ImagePreview (5)

create file ImagePreview.js in the components folder
create a ImagePreview component (use Image from react-native) and assign the following styles: width: '100%', height: 200, resizeMode: 'cover'
keep in mind to handle passed source prop (use as source in the Image component)
export component (default export)
use component with local download and remote (https://github.com/karlhorky/my-favorite-food/blob/main/assets/pizza.jpg) sources in App.js

Button (8)

create file Button.js in the components folder
create a Button component (use TouchableOpacity and Text from react-native) and assign the following styles.
Wrapper (TouchableOpacity) :

{
    display: 'flex',
    alignItems: 'center',
    backgroundColor: '#ff9100',
    borderRadius: 10,
    padding: 20,
    width: '100%'
}

Label (Text):

{
    textTransform: 'uppercase',
    fontSize: 14,
    fontWeight: 'bold',
    color: 'white',
    textAlign: 'center'
}

keep in mind to handle passed onPress prop (use as onPress in the TouchableHighlight component)
keep in mind to handle passed label prop (use as text-value in the Text component)
export component (default export)
use component in App.js

Step 7 - Navigation (13)

There are multiple libraries to handle navigation in react-native. One of the most used is react-navigation. See the docs here
If you think of a website, you know that there different URLs that you can go to - some libraries call these Routes. In a mobile app you don't have URLs, but you can have different views, which we call "Screens".

install the following packages

npm install @react-navigation/native

expo install react-native-gesture-handler react-native-reanimated react-native-screens @react-native-community/masked-view

npm install @react-navigation/stack

we need to import react-native-gesture-handler at the top of our App.js file. Used for handling native touch and gestures in react-navigation

import 'react-native-gesture-handler';

create NavigatioContainer in App.js

import { NavigationContainer } from '@react-navigation/native';

...

<NavigationContainer>{/* Rest of your app code */}</NavigationContainer>

add Stack to the Navigation

import { createStackNavigator } from '@react-navigation/stack';

...

const Stack = createStackNavigator();

...

const HomeScreen = () => {
  return (
    <View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
      <Text>Home Screen</Text>
    </View>
  );
}

....

<NavigationContainer>
    <Stack.Navigator>
        <Stack.Screen name="Home" component={HomeScreen} />
    </Stack.Navigator>
</NavigationContainer>

create folder screens
create file HomeScreen.js in the screens folder
make usage of our components and render some of these
copy the file HomeScreen.js and rename it to Detail.js (also rename the function component in the file)
copy the file HomeScreen.js and rename it to New.js (also rename the function component in the file)
create two new Stack.Screen entries for new Screens Detail and New

Step 8 - new components

Container (8)

create file Container.js in the components folder
create a Container component (use View from react-native) and assign the following styles (depending on the passed fill prop).
if fill is not provided assign these styles

{
    display: 'flex',
    flexDirection: 'column',
    padding: 20,
},

and these if fill is provided

{
    flex: 1,
    display: 'flex',
    flexDirection: 'column',
}

make sure to pass the children props to the View
make use of the component in our Screens

Screen (4)

create file Screen.js in the components folder
create a Screen component (use View from react-native) and assign the following styles

{
    display: 'flex',
    flexDirection: 'column',
    flex: 1,
    backgroundColor: '#fff'
}

make sure to pass the children props to the View
make use of the component in our Screens

Spacer (4)

create file Spacer.js in the components folder
create a Spacer component (use View from react-native) and assign the following styles

{
    height: 25,
    width: 25
}

make use of the component in our Screens

Header (10)

create file Header.js in the components folder
install expo install expo-constants (docs)
create the following component

import React from 'react';
import { SafeAreaView, StyleSheet, View, Text } from 'react-native';
import Constants from 'expo-constants';

const headerStyles = StyleSheet.create({
  safeAreaView: {
    backgroundColor: '#ff9100',
    borderBottomRightRadius: 20,
    borderBottomLeftRadius: 20,
  },
  wrapper: {
    paddingHorizontal: 20,
    paddingTop: Constants.statusBarHeight + 30,
    paddingBottom: 40,
  },
  label: {
    fontSize: 25,
    color: 'white',
    fontWeight: 'bold',
    textAlign: 'center',
  },
});

const Header = (props) => (
  <SafeAreaView style={headerStyles.safeAreaView}>
    <View style={headerStyles.wrapper}>
      <Text style={headerStyles.label}>{props.label}</Text>
    </View>
  </SafeAreaView>
);

FoodItem (14)

create file FoodItem.js in the components folder
create the following component

import React from 'react';
import { StyleSheet, View, Text, Image, TouchableOpacity } from 'react-native';
import Spacer from './Spacer';

const foodItemStyles = StyleSheet.create({
  wrapper: {
    display: 'flex',
    flexDirection: 'row',
    alignItems: 'center',
    padding: 10,
    borderBottomColor: 'lightgray',
    borderBottomWidth: 1,
  },
  image: {
    marginRight: 10,
    height: 50,
    width: 50,
  },
  title: { fontSize: 20, color: 'black', textAlign: 'left' },
});

const FoodItem = (props) => (
  <TouchableOpacity onPress={() => props.onPress()}>
    <View style={foodItemStyles.wrapper}>
      <Image
        resizeMode="cover"
        source={{
          uri: props.item.image,
        }}
        style={foodItemStyles.image}
      />
      <Text style={foodItemStyles.title}>{props.item.title}</Text>
    </View>
  </TouchableOpacity>
);

Input (12)

create file Input.js in the components folder
create a Input component (use TextInput from react-native) and assign the following styles

{
    borderColor: '#ff9100',
    borderWidth: 1,
    borderRadius: 10,
    paddingHorizontal: 20,
    paddingVertical: 12
}

make sure to pass the value, onChangeText and placeholder props to the TextInput
make use of the component in our Screens

Step 9 - Async Storage (15)

An asynchronous, unencrypted, persistent, key-value storage API.

install expo install @react-native-community/async-storage (docs)
create some helper functions to store and read from Async Storage
create folder helpers
create file storage.js in the helpers Screen
import Async Storage

import AsyncStorage from '@react-native-community/async-storage';

define a storage key for the key-value pair

const STORAGE_KEY = 'my-favorite-food/items';

storeData

export const storeData = async (value) => {
  try {
    const json = JSON.stringify(value);
    await AsyncStorage.setItem(STORAGE_KEY, json);
  } catch (error) {
    console.log(error);
  }
};

getData

export const getData = async () => {
  try {
    const json = await AsyncStorage.getItem(STORAGE_KEY);
    if (json === null) return null;
    return JSON.parse(json);
  } catch (error) {
    console.log(error);
  }
};

addData

export const addData = async (value) => {
  let data = [];
  const existing = await getData();
  if (existing) data = [...existing];
  data.push(value);
  await storeData(data);
};

Step 10 - combine storage, navigation, states (14)

we need to combine everything and make sure we have the following code for the different screen
Home Screen

import React, { useEffect, useLayoutEffect, useState } from 'react';
import Button from '../components/Button';
import Screen from '../components/Screen';
import Spacer from '../components/Spacer';
import { Headline, Paragraph } from '../components/Text';
import Header from '../components/Header';
import Container from '../components/Container';
import FoodItem from '../components/FoodItem';
import { useFocusEffect, useNavigation } from '@react-navigation/native';
import { getData } from '../helpers/storage';
import { ScrollView } from 'react-native';

const Home = () => {
  const navigation = useNavigation();
  const [items, setItems] = useState([]);
  useFocusEffect(() => {
    getData().then((data) => {
      if (data) setItems(data);
    });
  });
  return (
    <Screen>
      <Header label="In the mood for food?" />
      <Container fill>
        {items.length > 0 && (
          <ScrollView style={{ flex: 1 }}>
            <Container>
              {items.map((item, index) => (
                <FoodItem
                  key={index}
                  item={item}
                  onPress={() => navigation.navigate('Detail', { item })}
                />
              ))}
            </Container>
          </ScrollView>
        )}
      </Container>
      <Container>
        <Button
          label="add food"
          onPress={() => {
            navigation.navigate('New');
          }}
        />
      </Container>
    </Screen>
  );
};

export default Home;

Detail Screen

import React from 'react';
import Button from '../components/Button';
import Screen from '../components/Screen';
import Spacer from '../components/Spacer';
import { Headline } from '../components/Text';
import Header from '../components/Header';
import Container from '../components/Container';
import { ScrollView } from 'react-native';
import { addData } from '../helpers/storage';
import { useNavigation } from '@react-navigation/native';
import ImagePreview from '../components/ImagePreview';

const Detail = (props) => {
  const navigation = useNavigation();
  const { params } = props.route;
  return (
    <Screen>
      <Header label={params.item.title} />
      <Container fill>
        <ScrollView style={{ flex: 1 }}>
          <Container>
            {params.item.image && (
              <ImagePreview
                source={{
                  uri: params.item.image,
                }}
              />
            )}
          </Container>
        </ScrollView>
      </Container>
      <Container>
        <Button label="go back" onPress={() => navigation.goBack()} />
      </Container>
    </Screen>
  );
};

export default Detail;

New Screen

import React, { useState } from 'react';
import Button from '../components/Button';
import Screen from '../components/Screen';
import Spacer from '../components/Spacer';
import { Headline } from '../components/Text';
import Header from '../components/Header';
import Container from '../components/Container';
import { ScrollView } from 'react-native';
import { addData } from '../helpers/storage';
import { useNavigation } from '@react-navigation/native';
import * as ImagePicker from 'expo-image-picker';
import ImagePreview from '../components/ImagePreview';
import Input from '../components/Input';

const New = () => {
  const navigation = useNavigation();
  const [title, setTitle] = useState('');
  const [image, setImage] = useState(null);

  const selectImage = async () => {
    let permissionResult = await ImagePicker.requestCameraRollPermissionsAsync();
    if (permissionResult.granted === false) {
      alert('Permission to access camera roll is required!');
      return;
    }
    let pickerResult = await ImagePicker.launchImageLibraryAsync();
    if (pickerResult.cancelled === true) {
      return;
    }
    setImage(pickerResult.uri);
  };

  const save = async () => {
    await addData({ title, image });
    navigation.goBack();
  };
  return (
    <Screen>
      <Header label="What food do you like most?" />
      <Container fill>
        <ScrollView style={{ flex: 1 }}>
          <Container>
            <Input
              value={title}
              onChangeText={(text) => setTitle(text)}
              placeholder={'insert Title'}
            />
            <Spacer />
            {image && (
              <Fragment>
                <ImagePreview
                  source={{
                    uri: image,
                  }}
                />
                <Spacer />
              </Fragment>
            )}
            <Button label="select image" onPress={() => selectImage()} />
          </Container>
        </ScrollView>
      </Container>
      <Container>
        <Button
          label="save"
          disabled={title === '' || !image}
          onPress={() => save()}
        />
      </Container>
    </Screen>
  );
};

export default New;

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