A StyleSheet is an abstraction similar to CSS StyleSheets

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

const App = () => (
  <View style={styles.container}>
    <Text style={styles.title}>React Native</Text>
  </View>
);

const styles = StyleSheet.create({
  container: {
    flex: 1,
    padding: 24,
    backgroundColor: '#eaeaea',
  },
  title: {
    marginTop: 16,
    paddingVertical: 8,
    borderWidth: 4,
    borderColor: '#20232a',
    borderRadius: 6,
    backgroundColor: '#61dafb',
    color: '#20232a',
    textAlign: 'center',
    fontSize: 30,
    fontWeight: 'bold',
  },
});

export default App;

Code quality tips:

By moving styles away from the render function, you’re making the code easier to understand.
Naming the styles is a good way to add meaning to the low level components in the render function.

Reference

Methods

compose()

static compose(style1: Object, style2: Object): Object | Object[];

Combines two styles such that style2 will override any styles in style1. If either style is falsy, the other one is returned without allocating an array, saving allocations and maintaining reference equality for PureComponent checks.

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

const App = () => (
  <View style={container}>
    <Text style={text}>React Native</Text>
  </View>
);

const page = StyleSheet.create({
  container: {
    flex: 1,
    padding: 24,
    backgroundColor: '#fff',
  },
  text: {
    fontSize: 30,
    color: '#000',
  },
});

const lists = StyleSheet.create({
  listContainer: {
    flex: 1,
    backgroundColor: '#61dafb',
  },
  listItem: {
    fontStyle: 'italic',
    fontWeight: 'bold',
  },
});

const container = StyleSheet.compose(page.container, lists.listContainer);
const text = StyleSheet.compose(page.text, lists.listItem);

export default App;

create()

static create(styles: Object): Object;

Creates a StyleSheet style reference from the given object.

flatten()

static flatten(style: Object[]): Object;

Flattens an array of style objects, into one aggregated style object. Alternatively, this method can be used to lookup IDs, returned by StyleSheet.register.

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

const App = () => (
  <View style={page.container}>
    <Text style={flattenStyle}>React Native</Text>
    <Text>Flatten Style</Text>
    <Text style={page.code}>{JSON.stringify(flattenStyle, null, 2)}</Text>
  </View>
);

const page = StyleSheet.create({
  container: {
    flex: 1,
    padding: 24,
    alignItems: 'center',
  },
  text: {
    color: '#000',
    fontSize: 14,
    fontWeight: 'bold',
  },
  code: {
    marginTop: 12,
    padding: 12,
    borderRadius: 8,
    color: '#666',
    backgroundColor: '#eaeaea',
  },
});

const typography = StyleSheet.create({
  header: {
    color: '#61dafb',
    fontSize: 30,
    marginBottom: 36,
  },
});

const flattenStyle = StyleSheet.flatten([page.text, typography.header]);

export default App;

This method internally uses StyleSheetRegistry.getStyleByID(style) to resolve style objects represented by IDs. Thus, an array of style objects (instances of StyleSheet.create()), are individually resolved to, their respective objects, merged as one and then returned. This also explains the alternative use.

Properties

absoluteFill

A very common pattern is to create overlays with position absolute and zero positioning (position: 'absolute', left: 0, right: 0, top: 0, bottom: 0), so absoluteFill can be used for convenience and to reduce duplication of these repeated styles. If you want, absoluteFill can be used to create a customized entry in a StyleSheet, e.g.:

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

const App = () => (
  <View style={styles.container}>
    <View style={styles.box1}>
      <Text style={styles.text}>1</Text>
    </View>
    <View style={[styles.box2, StyleSheet.absoluteFill]}>
      <Text style={styles.text}>2</Text>
    </View>
    <View style={styles.box3}>
      <Text style={styles.text}>3</Text>
    </View>
  </View>
);

const styles = StyleSheet.create({
  container: {
    flex: 1,
  },
  box1: {
    position: 'absolute',
    top: 40,
    left: 40,
    width: 100,
    height: 100,
    backgroundColor: 'red',
  },
  box2: {
    width: 100,
    height: 100,
    backgroundColor: 'blue',
  },
  box3: {
    position: 'absolute',
    top: 120,
    left: 120,
    width: 100,
    height: 100,
    backgroundColor: 'green',
  },
  text: {
    color: '#FFF',
    fontSize: 80,
  },
});

export default App;

absoluteFillObject

Sometimes you may want absoluteFill but with a couple tweaks - absoluteFillObject can be used to create a customized entry in a StyleSheet, e.g.:

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

const App = () => (
  <View style={styles.container}>
    <View style={styles.box1}>
      <Text style={styles.text}>1</Text>
    </View>
    <View style={styles.box2}>
      <Text style={styles.text}>2</Text>
    </View>
    <View style={styles.box3}>
      <Text style={styles.text}>3</Text>
    </View>
  </View>
);

const styles = StyleSheet.create({
  container: {
    flex: 1,
  },
  box1: {
    position: 'absolute',
    top: 40,
    left: 40,
    width: 100,
    height: 100,
    backgroundColor: 'red',
  },
  box2: {
    ...StyleSheet.absoluteFillObject,
    top: 120,
    left: 50,
    width: 100,
    height: 100,
    backgroundColor: 'blue',
  },
  box3: {
    ...StyleSheet.absoluteFillObject,
    top: 120,
    left: 120,
    width: 100,
    height: 100,
    backgroundColor: 'green',
  },
  text: {
    color: '#FFF',
    fontSize: 80,
  },
});

export default App;

hairlineWidth

This is defined as the width of a thin line on the platform. It can be used as the thickness of a border or division between two elements. Example:

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

const App = () => (
  <View style={styles.container}>
    <Text style={styles.row}>React</Text>
    <Text style={styles.row}>Native</Text>
  </View>
);

const styles = StyleSheet.create({
  container: {
    flex: 1,
    padding: 24,
  },
  row: {
    padding: 4,
    borderBottomColor: 'red',
    borderBottomWidth: StyleSheet.hairlineWidth,
  },
});

export default App;

This constant will always be a round number of pixels (so a line defined by it can look crisp) and will try to match the standard width of a thin line on the underlying platform. However, you should not rely on it being a constant size, because on different platforms and screen densities its value may be calculated differently. A line with hairline width may not be visible if your simulator is downscaled.

​Reference

​Methods

​compose()

​create()

​flatten()

​Properties

​absoluteFill

​absoluteFillObject

​hairlineWidth