React Native First Application Hello World

Let's build our first React Native application on Windows as development operating system and Android as target operating system.

Steps to create React Native application

1. First, you have to start your emulator (Android Emulator) and make it live.

2. Create a directory (ReactNative) in your any drive.

3. Open "Command Prompt" and go to your ReactNative directory.

4. Write a command react-native init FirstApp to initialize your app "FirstApp".

5. Go to your directory location "FirstApp" and run the command react-native run-android. It will start Node server and launch your application in virtual device emulator.

Output:

View Code of React Native Application

Open your one of the favorite JavaScript supportable IDE and open App.js file inside your FirstApp application.

Code of default React Native first app.

App.js

1.  import React, {Component} from 'react';  
2. import {Platform, StyleSheet, Text, View} from 'react-native';  
3.   
4. const instructions = Platform.select({  
5.   ios: 'Press Cmd+R to reload,\n' + 'Cmd+D or shake for dev menu',  
6.   android:  
7.     'Double tap R on your keyboard to reload,\n' +  
8.     'Shake or press menu button for dev menu',  
9. });  
10.   
11. type Props = {};  
12. export default class App extends Component<Props> {  
13.   render() {  
14.     return (  
15.       <View style={styles.container}>  
16.         <Text style={styles.welcome}>Welcome to React Native!</Text>  
17.         <Text style={styles.instructions}>To get started, edit App.js</Text>  
18.         <Text style={styles.instructions}>{instructions}</Text>  
19.       </View>  
20.     );  
21.   }  
22. }  
23.   
24. const styles = StyleSheet.create({  
25.   container: {  
26.     flex: 1,  
27.     justifyContent: 'center',  
28.     alignItems: 'center',  
29.     backgroundColor: '#F5FCFF',  
30.   },  
31.   welcome: {  
32.     fontSize: 20,  
33.     textAlign: 'center',  
34.     margin: 10,  
35.   },  
36.   instructions: {  
37.     textAlign: 'center',  
38.     color: '#333333',  
39.     marginBottom: 5,  
40.   },  
41. });  

index.js

1. /** @format */  
2.   
3. import {AppRegistry} from 'react-native';  
4. import App from './App';  
5. import {name as appName} from './app.json';  
6.   
7. AppRegistry.registerComponent(appName, () => App);  

Create a simple React Native "Hello World" application

Create a simple "Hello World" app by editing App.js file of FirstApp.

Save the application and reload by simply pressing twice "R" or Ctrl+M (Reload).

App.js

1. import React, {Component} from 'react';  
2. import {Platform, StyleSheet, Text, View} from 'react-native';  
3.   
4. type Props = {};  
5. export default class App extends Component<Props> {  
6.   render() {  
7.     return (  
8.       <View>  
9.         <Text>Hello World</Text>  
10.       </View>  
11.     );  
12.   }  
13. }  

Output:

Edit simple React Native "Hello World" application

Edit React Native "Hello World" application using StyleSheet.

App.js

1. import React, {Component} from 'react';  
2. import {Platform, StyleSheet, Text, View} from 'react-native';  
3.   
4. type Props = {};  
5. export default class App extends Component<Props> {  
6.   render() {  
7.     return (  
8.       <View>  
9.         <Text style={styles.welcome}>Hello World</Text>  
10.       </View>  
11.     );  
12.   }  
13. }  
14. const styles = StyleSheet.create({  
15.   welcome: {  
16.     fontSize: 20,  
17.     textAlign: 'center',  
18.     margin: 10,  
19.   }  
20. });  

Output:

React Native Code Explanation

• import React, {Component} from 'react': imports the library and other components from react module and assign then to variable React.
• const instruction: sets to display the platform-specific message.
• export default class App extends Component: defines the classes that extend the React Component. The export default class modifier makes the class "public". This block of code defines the components that represent the user interface.
• render(): a function that returns a React element.
• return(): returns the result of layout and UI components.
• View: a container that supports the layout accessibility controls. It is a fundamental component for building the UI.
• Text: a React component for displaying text.
• style: a property used for styling the components using StyleSheet.
• styles: used to design individual components.
• {styles.instructions}>{instructions}:
• const styles = StyleSheet.create({}): The StyleSheet class creates the style object that controls the layout and appearance of components. It is similar to Cascading Style Sheets (CSS) used on the Web.