react-native

What is react-native?

React Native is an open-source mobile application framework created by Facebook. It is used to develop applications for Android, iOS, Web, and UWP by enabling developers to use React along with native platform capabilities. It allows for the development of mobile apps using JavaScript and React, offering a rich mobile UI library and tools to deliver a native app experience.

What are react-native's main functionalities?

UI Components

React Native provides a set of built-in core components like View, Text, and Image that you can use to build your app's UI. These components are pre-styled and ready to use, making it easy to develop complex UIs.

import { View, Text } from 'react-native';

function HelloWorldApp() {
  return (
    <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
      <Text>Hello, world!</Text>
    </View>
  );
}

Native Modules

Native Modules allow you to write modules in native code that can be called from JavaScript. This is useful for accessing platform-specific functionality that is not covered by the built-in React Native components.

import { NativeModules } from 'react-native';
const { CalendarModule } = NativeModules;

CalendarModule.createCalendarEvent('testName', 'testLocation');

Navigation

Navigation is essential for mobile apps. React Native can integrate with libraries like React Navigation to provide a way to navigate between screens.

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

const Stack = createStackNavigator();

function App() {
  return (
    <NavigationContainer>
      <Stack.Navigator initialRouteName='Home'>
        <Stack.Screen name='Home' component={HomeScreen} />
        <Stack.Screen name='Profile' component={ProfileScreen} />
      </Stack.Navigator>
    </NavigationContainer>
  );
}

Other packages similar to react-native

flutter

Flutter is Google's UI toolkit for crafting beautiful, natively compiled applications for mobile, web, and desktop from a single codebase. It is similar to React Native but uses Dart instead of JavaScript. Flutter provides its own widgets, which are drawn by the framework's own graphics engine.

ionic

Ionic is a popular framework for building hybrid mobile applications using web technologies like HTML, CSS, and JavaScript. It differs from React Native as it focuses on web technologies and uses Cordova or Capacitor to access native device features.

nativescript

NativeScript is an open-source framework for developing truly native mobile applications using JavaScript, TypeScript, Vue.js, or Angular. It provides direct access to native APIs and performance similar to React Native, but it allows for a broader choice of frameworks for building the UI.

README

React Native

React Native enables you to build world-class application experiences on native platforms using a consistent developer experience based on JavaScript and React. The focus of React Native is on developer efficiency across all the platforms you care about - learn once, write anywhere. Facebook uses React Native in multiple production apps and will continue investing in React Native.

Native iOS Components

With React Native, you can use the standard platform components such as UITabBar and UINavigationController on iOS. This gives your app a consistent look and feel with the rest of the platform ecosystem, and keeps the quality bar high. These components are easily incorporated into your app using their React component counterparts, such as TabBarIOS and NavigatorIOS.

var React = require('react-native');
var { TabBarIOS, NavigatorIOS } = React;

var App = React.createClass({
  render: function() {
    return (
      <TabBarIOS>
        <TabBarIOS.Item title="React Native" selected={true}>
          <NavigatorIOS initialRoute={{ title: 'React Native' }} />
        </TabBarIOS.Item>
      </TabBarIOS>
    );
  },
});

Asynchronous Execution

All operations between the JavaScript application code and the native platform are performed asynchronously, and the native modules can also make use of additional threads as well. This means we can decode images off of the main thread, save to disk in the background, measure text and compute layouts without blocking the UI, and more. As a result, React Native apps are naturally fluid and responsive. The communication is also fully serializable, which allows us to leverage Chrome Developer Tools to debug the JavaScript while running the complete app, either in the simulator or on a physical device.

Touch Handling

iOS has a very powerful system called the Responder Chain to negotiate touches in complex view hierarchies which does not have a universal analog on the web. React Native implements a similar responder system and provides high level components such as TouchableHighlight that integrate properly with scroll views and other elements without any additional configuration.

var React = require('react-native');
var { ScrollView, TouchableHighlight, Text } = React;

var TouchDemo = React.createClass({
  render: function() {
    return (
      <ScrollView>
        <TouchableHighlight onPress={() => console.log('pressed')}>
          <Text>Proper Touch Handling</Text>
        </TouchableHighlight>
      </ScrollView>
    );
  },
});

Flexbox and Styling

Laying out views should be easy, which is why we brought the flexbox layout model from the web to React Native. Flexbox makes it simple to build the most common UI layouts, such as stacked and nested boxes with margin and padding. React Native also supports common web styles, such as fontWeight, and the StyleSheet abstraction provides an optimized mechanism to declare all your styles and layout right along with the components that use them and apply them inline.

var React = require('react-native');
var { Image, StyleSheet, Text, View } = React;

var ReactNative = React.createClass({
  render: function() {
    return (
      <View style={styles.row}>
        <Image
          source={{uri: 'http://facebook.github.io/react/img/logo_og.png'}}
          style={styles.image}
        />
        <View style={styles.text}>
          <Text style={styles.title}>
            React Native
          </Text>
          <Text style={styles.subtitle}>
            Build high quality mobile apps using React
          </Text>
        </View>
      </View>
    );
  },
});
var styles = StyleSheet.create({
  row: { flexDirection: 'row', margin: 40 },
  image: { width: 40, height: 40, marginRight: 10 },
  text: { flex: 1, justifyContent: 'center'},
  title: { fontSize: 11, fontWeight: 'bold' },
  subtitle: { fontSize: 10 },
});

Polyfills

React Native is focused on changing the way view code is written. For the rest, we look to the web for universal standards and polyfill those APIs where appropriate. You can use npm to install JavaScript libraries that work on top of the functionality baked into React Native, such as XMLHttpRequest, window.requestAnimationFrame, and navigator.geolocation. We are working on expanding the available APIs, and are excited for the Open Source community to contribute as well.

var React = require('react-native');
var { Text } = React;

var GeoInfo = React.createClass({
  getInitialState: function() {
    return { position: 'unknown' };
  },
  componentDidMount: function() {
    navigator.geolocation.getCurrentPosition(
      (position) => this.setState({position}),
      (error) => console.error(error)
    );
  },
  render: function() {
    return (
      <Text>
        Position: {JSON.stringify(this.state.position)}
      </Text>
    );
  },
});

Extensibility

It is certainly possible to create a great app using React Native without writing a single line of native code, but React Native is also designed to be easily extended with custom native views and modules - that means you can reuse anything you've already built, and can import and use your favorite native libraries. To create a simple module in iOS, create a new class that implements the RCTBridgeModule protocol, and wrap the function that you want to make available to JavaScript in RCT_EXPORT_METHOD. Additionally, the class itself must be explicitly exported with RCT_EXPORT_MODULE();.

// Objective-C

#import "RCTBridgeModule.h"

@interface MyCustomModule : NSObject <RCTBridgeModule>
@end

@implementation MyCustomModule

RCT_EXPORT_MODULE();

// Available as NativeModules.MyCustomModule.processString
RCT_EXPORT_METHOD(processString:(NSString *)input callback:(RCTResponseSenderBlock)callback)
{
  callback(@[[input stringByReplacingOccurrencesOfString:@"Goodbye" withString:@"Hello"]]);
}
@end

// JavaScript

var React = require('react-native');
var { NativeModules, Text } = React;

var Message = React.createClass({
  getInitialState() {
    return { text: 'Goodbye World.' };
  },
  componentDidMount() {
    NativeModules.MyCustomModule.processString(this.state.text, (text) => {
      this.setState({text});
    });
  },
  render: function() {
    return (
      <Text>{this.state.text}</Text>
    );
  },
});

Custom iOS views can be exposed by subclassing RCTViewManager, implementing a -view method, and exporting properties with the RCT_EXPORT_VIEW_PROPERTY macro. Then a simple JavaScript file connects the dots.

// Objective-C

#import "RCTViewManager.h"

@interface MyCustomViewManager : RCTViewManager
@end

@implementation MyCustomViewManager
- (UIView *)view
{
  return [[MyCustomView alloc] init];
}

RCT_EXPORT_VIEW_PROPERTY(myCustomProperty);

@end

// JavaScript

var MyCustomView = createReactIOSNativeComponentClass({
  validAttributes: { myCustomProperty: true },
  uiViewClassName: 'MyCustomView',
});

Running the Examples

• git clone https://github.com/facebook/react-native.git
• cd react-native && npm install
• cd Examples

Now open any example and hit run in Xcode.

Further documentation, tutorials, and more on the React Native website.