2.2.3 修改JSX代码

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */

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

export default class MyProject8 extends Component {
  render() {
    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>
          Welcome to React Native!
        </Text>
        <Text style={styles.instructions}>
          To get started, edit index.android.js
        </Text>
        <Text style={styles.instructions}>
          Double tap R on your keyboard to reload,{'\n'}
          Shake or press menu button for dev menu
        </Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
  instructions: {
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});

AppRegistry.registerComponent('MyProject8', () => MyProject8);

修改之后：

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */

import React, { Component } from 'react';
import { //为了节约版面,将下面的多行写为一行,读者可以不修改
  AppRegistry,
  StyleSheet,
  Text,
  View
} from 'react-native';
let Dimensions = require('Dimensions');                     //请读者增加此行代码
let PixelRatio = require('PixelRatio');                     //请读者增加此行代码
let totalWidth = Dimensions.get('window').width;            //请读者增加此行代码
let totalHeight = Dimensions.get('window').height;          //请读者增加此行代码
let pixelRatio = PixelRatio.get();                          //请读者增加此行代码
export default class MyProject8 extends Component {
  render() {
    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>
          pixelRatio = {pixelRatio}                            //需要修改的第一行
        </Text>
        <Text style={styles.instructions}>
          totalHeight = {totalHeight};                         //需要修改的第二行
        </Text>
        <Text style={styles.instructions}>
          totalWidth = {totalWidth}                            //需要修改的第三行
          
        </Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
  instructions: {
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});

AppRegistry.registerComponent('MyProject8', () => MyProject8);