React Native has revolutionized the way we build mobile applications by allowing developers to use JavaScript and React to create rich, native apps for both iOS and Android. At the heart of React Native are its core components and APIs, which provide the necessary building blocks for creating mobile interfaces and functionalities.

Core Components

1. View

The most fundamental component in React Native is the View. It acts as a container that supports layout with flexbox, style, touch handling, and accessibility controls. Essentially, any non-text element in your app can be wrapped in a View.

Example:

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

const App = () => {
    return (
        <View style={styles.container}>
            <Text style={styles.text}>Hello, World!</Text>
        </View>
    );
};

const styles = StyleSheet.create({
    container: {
        flex: 1,
        justifyContent: 'center',
        alignItems: 'center',
        backgroundColor: '#F5FCFF',
    },
    text: {
        fontSize: 20,
    },
});

export default App;

2. Text

The Text component is used for displaying text in your application. It supports nesting, styling, and touch handling.

Example:

<Text style={{ fontSize: 24, color: 'blue' }}>Welcome to React Native!</Text>

3. Image

React Native makes it easy to display images with the Image component. You can load images from your local file system or from a URL.

Example:

import { Image } from 'react-native';

<Image
    source={{ uri: 'https://example.com/image.png' }}
    style={{ width: 100, height: 100 }}
/>

4. ScrollView

For displaying long lists of items, the ScrollView component is essential. It makes it easy to scroll through content that overflows the screen.

Example:

import { ScrollView } from 'react-native';

<ScrollView>
    <Text>Item 1</Text>
    <Text>Item 2</Text>
    <Text>Item 3</Text>
    // More items...
</ScrollView>

APIs

1. Fetch API

React Native comes with a built-in fetch API for making network requests. This is particularly useful for fetching data from web services.

Example:

fetch('https://api.example.com/data')
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error('Error:', error));

2. AsyncStorage

For local storage, React Native includes AsyncStorage, a simple, unencrypted, asynchronous, persistent, key-value storage system.

Example:

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

// Save data
AsyncStorage.setItem('userToken', 'abc123');

// Retrieve data
AsyncStorage.getItem('userToken')
    .then(value => console.log(value));

3. StyleSheet

Styles in React Native are created using the StyleSheet API, making it easy to define and organize your styles.

Example:

const styles = StyleSheet.create({
    container: {
        flex: 1,
        padding: 20,
    },
    button: {
        backgroundColor: '#007BFF',
        padding: 10,
        borderRadius: 5,
    },
});

4. Dimensions API

To get the size of the device screen, you can use the Dimensions API, which helps in making your app responsive.

Example:

import { Dimensions } from 'react-native';

const { width, height } = Dimensions.get('window');
console.log(`Width: ${width}, Height: ${height}`);

React Native's core components and APIs provide developers with a powerful toolkit for building mobile applications. With a strong understanding of these building blocks, your path to becoming proficient in React Native will be much clearer. So get started, build fantastic apps, and have fun coding!