用JavaScript构建原生移动应用：React Native 2nd版详解

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《Learning React Native: Building Native Mobile Apps with JavaScript (2nd Edition)》是一本由Bonnie Eisenman编写的权威指南，专为那些希望学习和实践使用React Native开发原生移动应用的人士设计。本书是第二版，针对的是JavaScript在构建现代移动应用中的实际应用，尤其是在React Native框架下。 React Native是由Facebook开发的开源框架，它允许开发者使用JavaScript和React库来编写原生iOS和Android应用。这与传统的原生开发相比，大大提高了开发效率，因为它基于组件化开发思想，使得代码重用和维护更加方便。第二版更新了React Native的最新技术和最佳实践，涵盖了从基础概念如组件、状态管理、UI组件到高级主题如性能优化、调试技巧以及集成第三方库的内容。作者Bonnie Eisenman以其丰富的经验和深入浅出的讲解，确保读者能够逐步掌握如何在JavaScript环境中构建功能齐全且用户体验优良的移动应用。本书适合已有JavaScript基础，尤其是对React有所了解的开发者阅读，也适合初学者通过实例学习React Native的开发流程。无论你是希望转行做移动开发，还是想提升现有技能，这本书都是不可或缺的参考资料。在版权方面，Learning React Native一书享有2018年Bonnie Eisenman的全部权利，且在美国印刷并由O'Reilly Media出版。对于教育、商业或销售推广用途，用户可以通过O'Reilly官网购买在线版本，或者联系公司的机构销售部门获取更多信息。该资源的PDF格式经过多种阅读器验证兼容性良好，包括FoxitReader、PDF-XChangeViewer、SumatraPDF和Firefox，读者可以放心下载使用。如果你想进一步了解本书的详细内容，可以在美国亚马逊官网进行搜索查询，以获取完整目录和更多购买选项。《Learning React Native》第二版是开发人员提升React Native技能，迈向原生移动应用开发新领域的宝贵资源。无论是为了个人项目还是职业发展，它都提供了实用的指导和深入的知识。

CHAPTER 1

What Is React Native?

React Native is a JavaScript framework for writing real, natively rendering mobile

applications for iOS and Android. It’s based on React, Facebook’s JavaScript library

for building user interfaces, but instead of targeting the browser, it targets mobile

platforms. In other words, it enables web developers to write mobile applications that

look and feel truly “native,” all from the comfort of a familiar JavaScript library. Plus,

because most of the code you write can be shared between platforms, React Native

makes it easy to simultaneously develop for both Android and iOS.

Similar to React for the web, React Native applications are written with a mixture of

JavaScript and XML-esque markup, known as JSX. Then, under the hood, the React

Native “bridge” invokes the native rendering APIs in Objective-C (for iOS) or Java

(for Android). Thus, your application will render using real mobile UI components,

not webviews, and will look and feel like any other mobile application. React Native

also exposes JavaScript interfaces for platform APIs, so your React Native apps can

access platform features like the phone camera or the user’s location.

The core React Native project supports writing mobile applications for both iOS and

Android. Community implementations also provide support for Windows, Ubuntu,

the web, and more.

In this book, we’ll build both Android and iOS apps with React Native. The vast

majority of the code we write will be cross-platform.

And, yes, you can really use React Native to build production-ready mobile applica‐

tions. Some anecdata: Facebook, Airbnb, Walmart, and Baidu are already using it in

production for user-facing applications.

Advantages of React Native

The fact that React Native renders using its host platform’s standard rendering APIs

distinguishes it from most existing methods of cross-platform application develop‐

ment, like Cordova or Ionic. Existing methods of writing mobile applications use

combinations of JavaScript, HTML, and CSS and typically render using webviews.

While this approach can work, it also comes with drawbacks, especially around per‐

formance. Additionally, these methods do not usually have access to the host plat‐

form’s set of native UI elements. When these frameworks do try to mimic native UI

elements, the results usually feel just a little off. In addition, reverse-engineering all

the fine details of things like animations takes an enormous amount of effort, and

they can quickly become outdated.

In contrast, React Native actually translates your markup to real, native UI elements,

leveraging existing means of rendering views on whatever platform you are working

with. Additionally, React works separately from the main UI thread, so your applica‐

tion can maintain high performance without sacrificing capability. The update cycle

in React Native is the same as in React: when props or state change, React Native re-

renders the views. The major difference between React Native and React in the

browser is that React Native does this by leveraging the UI libraries of its host plat‐

form, rather than using HTML and CSS markup.

For developers accustomed to working on the web with React, this means you can

write mobile apps with the performance and look and feel of a native application,

while using familiar tools. React Native also represents an improvement over normal

mobile development in two other areas: developer experience and cross-platform

development potential.

Developer Experience

If you’ve developed for mobile before, you might be surprised by how easy React

Native is to work with. The React Native team has baked strong developer tools and

meaningful error messages into the framework so that working with robust tools is a

natural part of your development experience.

For instance, because React Native is “just” JavaScript, you don’t need to rebuild your

application in order to see your changes reflected; instead, you can refresh your appli‐

cation just as you would any other web page. All of those minutes spent waiting for

your application to build can really add up, and in contrast React Native’s quick itera‐

tion cycle feels like a godsend.

Additionally, React Native lets you take advantage of intelligent debugging tools and

error reporting. If you are comfortable with Chrome or Safari’s developer tools

(Figure 1-1), you will be happy to know that you can use them for mobile develop‐

ment as well. Likewise, you can use whatever text editor you prefer for JavaScript

2 | Chapter 1: What Is React Native?

need on a specific platform, you may occasionally need to dip into Objective-C or

Java (we’ll cover how so-called native modules work in Chapter 7). But reusing code

across platforms is surprisingly easy with React Native. For example, the Facebook

Ads Manager application for Android shares 87% of its codebase with the iOS ver‐

sion. The final application we’ll look at in this book, a flashcard app, has total code

reuse between Android and iOS. It’s hard to beat that!

Risks and Drawbacks

As with anything, using React Native is not without its downsides, and whether or

not it is a good fit for your team really depends on your individual situation.

Because React Native introduces another layer to your project, it can make debugging

hairier, especially at the intersection of React and the host platform. We’ll cover

debugging for React Native in more depth in Chapter 9 and try to address some of

the most common issues.

Along the same lines, when updates are released for the host platform—say, a new

suite of APIs in a new version of Android—there will be a lag before they are fully

supported in React Native. The good news is that in the vast majority of cases, you

can implement support for missing APIs yourself, which we’ll cover in Chapter 7.

Also, if you do hit a roadblock, you won’t be locked in to using React Native—many

companies have successfully implemented hybrid approaches to app development.

Changing the platform you use to write your applications is a big choice. Still, I think

you’ll see that the benefits of React Native outweigh the risks.

Summary

React Native is an exciting framework that enables web developers to create robust

mobile applications using their existing JavaScript knowledge. It offers faster mobile

development and more efficient code sharing across iOS, Android, and the web

without sacrificing the end user’s experience or application quality. The tradeoff is

that it adds some complexity to your application setup. If your team can handle that

and wants to develop mobile applications for more than just one platform, you

should be looking at React Native.

In the next chapter, we go over some of the main ways in which React Native differs

from React for the web, and cover some key concepts. If you’d like to skip straight to

developing, feel free to jump to Chapter 3, in which we set up our development envi‐

ronment and write our very first React Native application.

4 | Chapter 1: What Is React Native?

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