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Core Components

Core Components

Core components are ready-to-use components available from React Native, which include <View>, <Text>, <Image>, <ScrollView>, <Button>, and <TextInput>.

<ScrollView> <Text>Some text</Text> <View> <Text>Some more text</Text> <Image source={{ uri: 'https://picsum.photos/64/64', }} /> </View> <TextInput defaultValue="You can type here" /> <Button onPress={() => { alert('You tapped the button!'); }} title="Press Me" /> </ScrollView>

Importing Core Components

You can import core components into your Expo project from the react-native package.

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

Core Components Optional Functionality

Core components may have more optional functionality, which you can configure through the props.

function App() { return ( {/* Text components can be with `numberofLines` prop */} <Text numberOfLines={1}> quam elementum pulvinar etiam non quam lacus suspendisse faucibus interdum posuere lorem ipsum dolor sit </Text> ); }

<View> Component

The <View> component is a generic “visible” container without any semantic meaning or noticeable performance impact, best translated as <div> from web.

function App() { return ( {/* Base layout structure */} <View style={{ flex: 1 }}> {/* Simple background color */} <View style={{ padding: 8, color: 'red' }}> <Text>Text with background color</Text> </View> {/* Space layout structure */} <View style={{ margin: 16 }} /> </View> ); }

<ScrollView> Component

The <ScrollView> component is a generic “visible” container with scrolling, but it’s less performant than <View>, making it less suitable for simple styling and short lines of text.

function App() { return ( <ScrollView> <Text style={{ margin: 16 }}>Scroll here to see more!</Text> <View style={{ marginTop: 1024 }} /> <Text style={{ margin: 16 }}>Made you look!</Text> </ScrollView> ); }

<Text> Component

The <Text> component is the only way to display text in React Native. These components can be nested to inherit and modify styling.

<Text style={{ height: 40, borderWidth: 1 }}> Here's some text! </Text>

<Image> Component

The <Image> component is an optimized way to render images from various sources, including remote HTTP access, local assets imported with require, and base64 encoded strings.

<Image source={require('./local/asset.jpg')} /> <Image source={{ uri: 'https://docs.expo.io/static/images/header/sdk.svg' }} /> <Image source={{ uri: 'data:image/png;base64,<base64-string>=' }} />

<TextInput> Component

The <TextInput> component can capture alphanumeric input from the user. Its behavior can be modified with the onChangeText prop, which accepts a function.

const [input, setInput] = useState(''); // example use of input console.log(input); return ( <TextInput placeholder="What is your name?" onChangeText={setInput} /> );

Business-Logic Focused Components

Creating business-logic focused components is done by “composing” components into one and connecting functionality by passing props and event handlers.

function ReadMoreParagraph(props) { const [isOpen, setOpen] = useState(false); return ( <View style={{ flex: 1, flexDirection: 'column' }}> <Text style={{ fontSize: 16 }} numberOfLines={!isOpen ? 2 : undefined}> {props.children} </Text> {!isOpen ? <Button title='Read More' onPress={() => setOpen(true)} /> : <Button title='Read Less' onPress={() => setOpen(false)} /> </View> ) }

Custom Components

Similar to React, it’s common to create custom components to wrap configuration and usage of core components.

const App = () => ( <View style={{ flex: 1, justifyContent: 'center' }}> <Box color="red" /> <Box color="green" /> <Box color="blue" /> </View> ); export const Box = (props) => ( <View style={{ width: 100, height: 100, backgroundColor: props.color }} /> );

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