September 2017
Introduction to
React Native
Nacho Martín

Nacho Martin
I write code at Limenius.
We build tailor-made projects,
and provide consultancy
and formation.
We are very happy with React and React Native.

Roadmap:
What is React Native
Starting a project
Working with Styles
Layout
Lists
Navigation
Networking
Touching the native side

What is React Native?

Fundamental premise of React
Give me a state and a render() method
that depends on it and forget about
how and when to render.*

Fundamental premise of React
Give me a state and a render() method
that depends on it and forget about
how and when to render.*
* Unless you want more control.

render() {
return (
<div className="App">
<button onClick={this.tick}>Click me!</button>
<span>Clicks: {this.state.count}</span>
</div>
)
}

render() {
return (
<div className="App">
<button onClick={this.tick}>Click me!</button>
<span>Clicks: {this.state.count}</span>
</div>
)
}
render() {
return (
<View style={…}>
<Button onPress={this.tick}>Click me!</Button>
<Text>Clicks: {this.state.count}</Text>
</View>
)
}

render() {
return (
<div className="App">
<button onClick={this.tick}>Click me!</button>
<span>Clicks: {this.state.count}</span>
</div>
)
}
render() {
return (
<View style={…}>
<Button onPress={this.tick}>Click me!</Button>
<Text>Clicks: {this.state.count}</Text>
</View>
)
}

render() {
return (
<div className="App">
<button onClick={this.tick}>Click me!</button>
<span>Clicks: {this.state.count}</span>
</div>
)
}
render() {
return (
<View style={…}>
<Button onPress={this.tick}>Click me!</Button>
<Text>Clicks: {this.state.count}</Text>
</View>
)
}
React Native

How is this possible
Reconciliation
Determines what parts
of the tree have changed

How is this possible
Reconciliation
Determines what parts
of the tree have changed
Rendering
Actually
updates the app

How is this possible
Reconciliation
Determines what parts
of the tree have changed
Rendering
Actually
updates the app
We can have several
renderers

React targets
Main
react-dom react-native
Web iOS android

React targets
Main
react-dom react-native
Web iOS android
But also

React targets
Main
react-dom react-native
Web iOS android
But also
react-art react-canvas react-three ReactLibertyreact-worker-dom

React targets
Main
react-dom react-native
Web iOS android
But also
react-art react-canvas react-three ReactLibertyreact-worker-dom
react-konsul raxreact-native react-blessedreact-tvml

React targets
Main
react-dom react-native
Web iOS android
But also
react-art react-canvas react-three ReactLibertyreact-worker-dom
react-konsul raxreact-native react-blessedreact-tvml
React-GLreact-vr react-hardware react-fs-renderer react-x11

React targets
Main
react-dom react-native
Web iOS android
But also
react-art react-canvas react-three ReactLibertyreact-worker-dom
react-konsul raxreact-native react-blessedreact-tvml
React-GLreact-vr react-hardware react-fs-renderer react-x11
redocx react-titanium React-Gibbon react-pdf react-test-renderer

React targets
Main
react-dom react-native
Web iOS android
But also
react-art react-canvas react-three ReactLibertyreact-worker-dom
react-konsul raxreact-native react-blessedreact-tvml
React-GLreact-vr react-hardware react-fs-renderer react-x11
redocx react-titanium React-Gibbon react-pdf react-test-renderer
ink react-sketchapp

React blessed

React blessed

React Sketch.app

React VR
Demo

How Native is React Native?
JS Thread
Business logic &
Description of what
components to render

How Native is React Native?
JS Thread Main Thread
UI manipulation
with native
components
Business logic &
Description of what
components to render

How Native is React Native?
JS Thread Main Thread
UI manipulation
with native
components
Business logic &
Description of what
components to render
Bridge

How much code can we reuse?
Tip: if you develop in one platform,
try it in the other from time to time
70%? 80%? 90%?

How to start a project

Option 1: create-react-native-app
$ npm install -g create-react-native-app
$ create-react-native-app AwesomeProject

Option 1: create-react-native-app
Only JS, no iOS or Android code
(outside node_modules)
If you want to modify native code, $ npm run eject
Uses the Expo app to test in real device
Meant to have a quick way of trying
react-native

Option 2: react-native init
$ npm install -g react-native-cli
$ react-native init AwesomeProject

Option 2: react-native init
Complete project with native code
More control
Needed to use things like CodePush
Doesn’t need external tools to publish to
the store

Getting our hands dirty

git clone https://github.com/Limenius/workshop-react-native.git
You are supposed to have done this
🙏
And then yarn install

git checkout dirtyhands
react-native run-ios
And then
Or
react-native run-android

git checkout dirtyhands
react-native run-ios
And then
Or
react-native run-android

Debug tools Cmd + d
(Cmd + r)

Play around
Open app/App.js with an editor
<Text style={styles.welcome}>Hi there!</Text>Change the text in
Try nesting
<Text>
<Text style={styles.welcome}>Hi there!</Text>
Amigo
</Text>
Try changing some styles
welcome: {
fontSize: 100,
textAlign: 'center',
margin: 10,
},
Try placing a console.log(‘hi’) before return(… and see it in
Chrome dev tools

Familiarize with errors
What happens if we…
remove a closing tag (</View>)
<View style={styles.container}>
Hi there!
</View>
put text not wrapped in <Text/>
try to comment a JSX line with //
return (
<View style={styles.container}>
<Text style={styles.welcome}>Hi there!</Text>
</View>
<View/>
)
have two root elements
use wrong properties for styles ( rename flex -> flexo )
remove the words export default

Basic components

git checkout elements
git reset HEAD --hard
(To discard your changes)

Exercise:
Play with the basic components
app/App.js

Exercise: Build new components
Can you build a new component combining others?
Ideas: Image with footer (<Text/>), two buttons that display different alerts
Can you pass props to that component?
Ideas: Pass the text of the footer with props, pass also the image, pass the titles of the buttons
Can your build a component with local state?
Ideas: Modify the counter to have a “minus 1” button

Style 💅

No CSS. Everything is JS
<View style={{
borderLeftColor: Colors.accent,
borderLeftWidth: 9,
backgroundColor: Colors.backgroundSection,
padding: 18,
paddingVertical: 9,
}}>
No class
No dimensions in pixels
No things like padding: 19 9 3 1
camelCased
Use constants

StyleSheet
<View style={Styles.headline}>
const Styles = StyleSheet.create({
headline: {
borderLeftColor: Colors.accent,
borderLeftWidth: 9,
backgroundColor: Colors.backgroundSection,
paddingLeft: 18,
paddingRight: 18,
paddingTop: 9,
paddingBottom: 9,
},
})

Combination
<View style={[Styles.headline, {backgroundColor: 'red'}]}>
const Styles = StyleSheet.create({
headline: {
borderLeftColor: Colors.accent,
borderLeftWidth: 9,
paddingLeft: 18,
paddingRight: 18,
paddingTop: 9,
paddingBottom: 9,
},
})

git checkout styles
(To discard your changes)
git reset HEAD --hard

We want to do this

Our first goal is to get this
(We will practice layouts in the next section)

components/MovieHeader.js
height: 210
fontWeight:‘bold’
fontSize: FontSizes.LargeTitle
48x48, rounded
backgroundColor: Colors.highlight
color: Colors.text
color: Colors.text
fontWeight:‘bold’
border: left, size 9, Colors.accent
padding: 9, 18
backgroundColor: Colors.backgroundSection

Exercise 1
84x84
Colors.text, bold
Container has: border at bottom size 1, Colors.subtleAccent
and background is 'white'
components/ListItemActor.js

Exercise 2
FontSizes.gigantic
Colors.background
Container has: a background with color: Colors.highlight
components/MainHeader.js
Image is 40x90
FontSizes.subhead
With weight ‘200’
Colors.background
Pro exercise:Think how would you add support for themes

Dimensions
import {
Dimensions,
} from 'react-native'
const windowSize = Dimensions.get('window')
mainImage: {
height: windowSize.height /3,
width: undefined
},
components/MovieHeader.js

Dimensions
import {
Dimensions,
} from 'react-native'
const windowSize = Dimensions.get('window')
mainImage: {
height: windowSize.height /3,
width: undefined
},
Our image height depends on the
Height of the window
Use sparingly
components/MovieHeader.js

Dimensions
import {
Dimensions,
} from 'react-native'
const windowSize = Dimensions.get('window')
mainImage: {
height: windowSize.height /3,
width: undefined
},
Our image height depends on the
Height of the window
Use sparingly
Exercise: Can you make another style dependant of
Dimensions?
What will happen if the device is rotated?
Can you find anything in the documentation to fix it?
components/MovieHeader.js

Further reading
https://www.okgrow.com/posts/react-native-styling-tips
https://madebymany.com/stories/a-year-of-react-native-styling-part-1
https://medium.com/robin-powered/introducing-glamorous-for-react-native-1b8365e7f33f
https://github.com/styled-components/styled-components
Explore libraries to do CSS in JS

Layouts

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flexDirection: ‘column' flexDirection: ‘row’
(Default)

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flexDirection: ‘column' flexDirection: ‘row’
(Default)
main direction
crossdirection

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flexDirection: ‘column' flexDirection: ‘row’
(Default)
main direction
crossdirection
cross direction
maindirection

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flexDirection: ‘column’
(Default)
‘flex-start’ ‘flex-end’ ‘center' ‘space-around’ ‘space-between’
flexDirection: ‘row’
(Default)
‘flex-start’ ‘flex-end’ ‘center' ‘space-around’ ‘space-between’

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flexDirection: ‘column’
(Default)
‘flex-start’ ‘flex-end’ ‘center' ‘stretch’ ‘baseline’
flexDirection: ‘row’
(Default)
‘flex-start’ ‘flex-end’ ‘center' ‘stretch’ ‘baseline’

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flexDirection: ‘row’
‘baseline’

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flexDirection: ‘column’
alignSelf: ’end’

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flex: 1
flex: 0
flex: 0

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flex: 5
flex: 2
flex: 3

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flex: 0.5
flex: 0.2
flex: 0.3

This is flexbox realm
flexDirection
justifyContent
alignItems
alignSelf
flex
alignContent
flexBasis
flexGrow
flexShrink
flexWrap
flex: 25
flex: 10
flex: 15

git checkout layout
(To discard your changes)
git reset HEAD --hard

Our goal

app/components/MovieHeader.js

app/components/MovieHeader.js

18
Exercise 1
app/components/ListItemActor.js

Exercise 2
Hint: create subviews if you need them
Optional: can you come up with a different layout for any of our three components?
app/components/MainHeader.js

Further reading
https://facebook.github.io/yoga/docs/getting-started/
Docs:
https://github.com/jondot/ReactNativeKatas
Very good practice:

Lists

Lists are important in mobile

Naive lists, as in the web
export default class Movie extends Component {
constructor(props) {
super(props)
this.state = {
movie: movies.find((movie) => movie.name === 'Pulp Fiction')
}
}
render() {
return (
<View>
<MovieHeader movie={this.state.movie}/>
{ this.state.movie.actors.map(actor => (
<ListItem key={actor} name={actor} image={actors[actor].image}/>
))}
</View>
)
}
}
app/components/Movie.js

Naive lists, as in the web
export default class Movie extends Component {
constructor(props) {
super(props)
this.state = {
movie: movies.find((movie) => movie.name === 'Pulp Fiction')
}
}
render() {
return (
<View>
<MovieHeader movie={this.state.movie}/>
{ this.state.movie.actors.map(actor => (
<ListItem key={actor} name={actor} image={actors[actor].image}/>
))}
</View>
)
}
}
Important to help the reconciler do its work
app/components/Movie.js

Exercise
git checkout lists
Can you build a list of movies in
app/components/MovieList.js ?
(To discard your changes)
git reset HEAD --hard

FlatList
Highly optimized List component
Features:
• Scroll loading (onEndReached).
• Pull to refresh (onRefresh / refreshing).
• Configurable viewability (VPV) callbacks (onViewableItemsChanged / viewabilityConfig).
• Horizontal mode (horizontal).
• Intelligent item and section separators.
• Multi-column support (numColumns)
• scrollToEnd, scrollToIndex, and scrollToItem
• Better Flow typing.

FlatList
render() {
return (
<View>
<MovieHeader movie={this.state.movie}/>
<FlatList
data={this.state.movie.actors}
renderItem={({item}) =>
<ListItem name={item} image={this.state.actors[item].image}/>
}
/>
</View>
)
}
app/components/Movie.js

FlatList

FlatList
What about the keys?

FlatList
What about the keys?
<FlatList
data={this.state.movie.actors}
keyExtractor={item => item}
renderItem={({item}) =>
<ListItem name={item} image={this.state.actors[item].image}/>
}
/>

FlatList
What about the keys?
<FlatList
data={this.state.movie.actors}
keyExtractor={item => item}
renderItem={({item}) =>
<ListItem name={item} image={this.state.actors[item].image}/>
}
/>

FlatList
Scrolleable area
<FlatList
data={this.state.movie.actors}
keyExtractor={item => item}
renderItem={({item}) =>
<ListItem name={item} image={this.state.actors[item].image}/>
}
/>
<MovieHeader movie={this.state.movie}/>

FlatList
Desired scrolleable area

FlatList
Desired scrolleable area
<FlatList
data={this.state.movie.actors}
ListHeaderComponent={<MovieHeader movie={this.state.movie}/>}
keyExtractor={item => item}
renderItem={({item}) =>
<ListItem name={item} image={this.state.actors[item].image}/>
}
/>

FlatList
Desired scrolleable area
<FlatList
data={this.state.movie.actors}
ListHeaderComponent={<MovieHeader movie={this.state.movie}/>}
keyExtractor={item => item}
renderItem={({item}) =>
<ListItem name={item} image={this.state.actors[item].image}/>
}
/>

Exercise
Can you use FlatList in
app/components/MovieList.js ?
git checkout flatLists
item => item
reminder
In this case works as
function(item) {
return item
}
git reset HEAD —hard
(To discard your changes)

Further reading
https://facebook.github.io/react-native/blog/2017/03/13/
better-list-views.html
Read the docs of the components:
FlatList
SectionList
VirtualizedList

Navigation

Navigation

react-navigation

Several options
StackNavigator TabNavigator DrawerNavigator Or combine them

Several options
StackNavigator TabNavigator DrawerNavigator Or combine them

Several options
StackNavigator TabNavigator DrawerNavigator Or combine them

Several options
StackNavigator TabNavigator DrawerNavigator Or combine them

Let’s do it
git checkout navigation
(To discard your changes)
git reset HEAD --hard

Let’s do it
const App = StackNavigator({
Home: { screen: MovieList },
Movie: { screen: Movie },
}, {
navigationOptions: {
headerTintColor: Colors.accent,
headerStyle: Styles.header,
}
})
app/App.js

Let’s do it
const App = StackNavigator({
Home: { screen: MovieList },
Movie: { screen: Movie },
}, {
navigationOptions: {
headerTintColor: Colors.accent,
headerStyle: Styles.header,
}
})
app/App.js
export default class MovieList extends Component {
static navigationOptions = {
title: 'Movies',
}
//…
app/components/MovieList.js

Let’s do it
const App = StackNavigator({
Home: { screen: MovieList },
Movie: { screen: Movie },
}, {
navigationOptions: {
headerTintColor: Colors.accent,
headerStyle: Styles.header,
}
})
app/App.js
export default class MovieList extends Component {
static navigationOptions = {
title: 'Movies',
}
//…
app/components/MovieList.js
<FlatList
data={this.state.movies}
ListHeaderComponent={<MainHeader/>}
keyExtractor={item => item.name}
renderItem={({item}) =>
<TouchableHighlight
underlayColor={Colors.subtleAccent}
activeOpacity={0.5}
onPress={() => navigate('Movie', {name: item.name})}
>
<View>
<ListItem name={item.name} image={item.image}/>
</View>
</TouchableHighlight>
}
/>
In render()

Let’s do it
const App = StackNavigator({
Home: { screen: MovieList },
Movie: { screen: Movie },
}, {
navigationOptions: {
headerTintColor: Colors.accent,
headerStyle: Styles.header,
}
})
app/App.js
export default class MovieList extends Component {
static navigationOptions = {
title: 'Movies',
}
//…
app/components/MovieList.js
<FlatList
data={this.state.movies}
ListHeaderComponent={<MainHeader/>}
keyExtractor={item => item.name}
renderItem={({item}) =>
<TouchableHighlight
underlayColor={Colors.subtleAccent}
activeOpacity={0.5}
onPress={() => navigate('Movie', {name: item.name})}
>
<View>
<ListItem name={item.name} image={item.image}/>
</View>
</TouchableHighlight>
}
/>
In render()

Exercise
Can you make a navigation transition from Movie to
app/components/Actor ?
Steps:
- Declare the screen in app/App.js
- Use a TouchableHighlight to capture onPress in the actors
list of <Movie/>
- Provide an appropriate title in <Actor/>
- Make the actor displayed based on
props.navigation.state.params.name
Optional: have a look at
https://reactnavigation.org/docs/navigators/stack#StackNavigatorConfig
And tweak the navigation (Ideas: mode modal, add something to headerRight)

Networking

Networking
React-native uses the Fetch API
If you already know it, you are all set 🎉

Let’s do it
componentDidMount() {
return fetch(baseUrl + '/movies')
.then((response) => response.json())
.then((responseJson) => {
this.setState({
isLoading: false,
movies: responseJson,
})
})
.catch((error) => {
console.error(error);
})
}
app/components/MovieList.js

Let’s do it
git checkout networking
yarn start-server
(To discard your changes)
git reset HEAD --hard

Further reading
https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch
Docs:
https://github.com/mzabriskie/axios
Additional libraries:

Interactive

Our goal

Working with state
Not specific of React Native,
we just use what we know of React

Let’s do it
git checkout interactive
(To discard your changes)
git reset HEAD --hard

Modify the native side

Cases where it is needed
Installing packages that have a native side
Making our own changes or components
Installing assets, such as fonts
…

Simple case
Install this font

Let’s do it
"rnpm": {
"assets": ["./assets/fonts/"]
}
package.json
git checkout mod-native
(To discard your changes)
git reset HEAD --hard

Let’s do it
"rnpm": {
"assets": ["./assets/fonts/"]
}
package.json
react-native link
git checkout mod-native
(To discard your changes)
git reset HEAD --hard

Assets linked
Changes to be committed:
(use "git reset HEAD <file>..." to unstage)
new file: android/app/src/main/assets/fonts/OleoScript-Bold.ttf
new file: android/app/src/main/assets/fonts/OleoScript-Regular.ttf
modified: ios/travolta.xcodeproj/project.pbxproj
modified: ios/travolta/Info.plist
modified: package.json

Summary:
What is React Native
Starting a project
Working with Styles
Layout
Lists
Navigation
Networking
Touching the native side

Thanks! @nacmartin
nacho@limenius.com