App Development with React Native CLI

Introduction to React Native CLI

React Native is one of the most famous open-source hybrid frameworks to build apps for Android, iOS, and web platforms using JavaScript with a single codebase.

The name “React Native” is composed of two words: React and Native. “React” states the use of the React app development environment, and “Native” represents the use of native Android/iOS/Web UI widgets to develop apps for better performance. React Native interacts with the Native platform at runtime via JavaScript to construct the native view for React Native UI components. React Native also offers ready-to-use inbuilt APIs for UI development such as <ScrollView><FlatList><ImageView>, etc. to develop apps.

Prerequisites

React Native follows the similar development structure and tools of React, so this guide assumes that you have the basics knowledge of following technologies and tools.

Technologies
  • Basics of JavaScript
  • HTML, Objects, and EcmaScript 6 (ES6 classes and arrow functions, etc.)
Tools
  • Node.js
  • Command line interface (CLI)

To work with React Native, you will need to have an understanding of JavaScript fundamentals. If you’re new to JavaScript or need a refresher, you can dive in or brush up at Mozilla Developer Network.

 Where sensible, we have linked to resources and articles that go more in depth.

Setting up the developer environment

This blog will help you install and build your first React Native app.

Follow these instructions if you need to build native code in your project. For example, if you are integrating React Native into an existing application, or if you “ejected” from Expo, you’ll need this section.

The instructions are a bit different depending on your development operating system, and whether you want to start developing for iOS or Android. If you want to develop for both Android and iOS, that’s fine – you can pick one to start with, since the setup is a bit different.

Development OS

macOS

Windows

Linux

Target OS

Android

iOS

Installing dependencies

You will need Node, the React Native command line interface, a JDK, and Android Studio.

While you can use any editor of your choice to develop your app, you will need to install Android Studio in order to set up the necessary tooling to build your React Native app for Android.

Node, JDK

We recommend installing Node via Chocolatey, a popular package manager for Windows.

If you want to be able to switch between different Node versions, you might want to install Node via nvm-windows, a Node version manager for Windows.

React Native also requires Java SE Development Kit (JDK), which can be installed using Chocolatey as well.

Open an Administrator Command Prompt (right click Command Prompt and select “Run as Administrator”), then run the following command:

choco install -y nodejs.install openjdk8

If you’re using the latest version of Java Development Kit, you’ll need to change the Gradle version of your project so it can recognize the JDK. You can do that by going to {project root folder}\android\gradle\wrapper\gradle-wrapper.properties and changing the distributionUrl value to upgrade the Gradle version.

Android development environment

Setting up your development environment can be somewhat tedious if you’re new to Android development. If you’re already familiar with Android development, there are a few things you may need to configure. In either case, please make sure to carefully follow the next few steps.

1. Install Android Studio

Download and install Android Studio. While on Android Studio installation wizard, make sure the boxes next to all of the following items are checked:

  • Android SDK
  • Android SDK Platform
  • Android Virtual Device
  • If you are not already using Hyper-V: Performance (Intel ® HAXM) (See here for AMD or Hyper-V)

Then, click “Next” to install all of these components.

If the checkboxes are grayed out, you will have a chance to install these components later on.

Once setup has finalized and you’re presented with the Welcome screen, proceed to the next step.

2. Install the Android SDK

Android Studio installs the latest Android SDK by default. Building a React Native app with native code, however, requires the Android 10 (Q) SDK in particular. Additional Android SDKs can be installed through the SDK Manager in Android Studio.

To do that, open Android Studio, click on “Configure” button and select “SDK Manager”.

Image titled Add Images in Android Studio Step 2

Select the “SDK Platforms” tab from within the SDK Manager, then check the box next to “Show Package Details” in the bottom right corner. Look for and expand the Android 10 (Q) entry, then make sure the following items are checked:

  • Android SDK Platform 29
  • Intel x86 Atom_64 System Image or Google APIs Intel x86 Atom System Image

Next, select the “SDK Tools” tab and check the box next to “Show Package Details” here as well. Look for and expand the “Android SDK Build-Tools” entry, then make sure that 29.0.2 is selected.

Finally, click “Apply” to download and install the Android SDK and related build tools.

3. Configure the ANDROID_HOME environment variable

The React Native tools require some environment variables to be set up in order to build apps with native code.

  1. Open the Windows Control Panel.
  2. Click on User Accounts, then click User Accounts again
  3. Click on Change my environment variables
  4. Click on New… to create a new ANDROID_HOME user variable that points to the path to your Android SDK:
ANDROID_HOME Environment Variable

The SDK is installed, by default, at the following location:

%LOCALAPPDATA%\Android\Sdk

You can find the actual location of the SDK in the Android Studio “Settings” dialog, under Appearance & Behavior → System Settings → Android SDK.

Open a new Command Prompt window to ensure the new environment variable is loaded before proceeding to the next step.

  1. Open powershell
  2. Copy and paste Get-ChildItem -Path Env:\ into powershell
  3. Verify ANDROID_HOME has been added

4. Add platform-tools to Path

  1. Open the Windows Control Panel.
  2. Click on User Accounts, then click User Accounts again
  3. Click on Change my environment variables
  4. Select the Path variable.
  5. Click Edit.
  6. Click New and add the path to platform-tools to the list.

The default location for this folder is:

%LOCALAPPDATA%\Android\Sdk\platform-tools

React Native Command Line Interface

React Native has a built-in command line interface. Rather than install and manage a specific version of the CLI globally, we recommend you access the current version at runtime using npx, which ships with Node.js. With npx react-native <command>, the current stable version of the CLI will be downloaded and executed at the time the command is run.

Creating a new application

If you previously installed a global react-native-cli package, please remove it as it may cause unexpected issues.

React Native has a built-in command line interface, which you can use to generate a new project. You can access it without installing anything globally using npx, which ships with Node.js. Let’s create a new React Native project called “AwesomeProject”:

npx react-native init AwesomeProject

Preparing the Android device

You will need an Android device to run your React Native Android app. This can be either a physical Android device, or more commonly, you can use an Android Virtual Device which allows you to emulate an Android device on your computer.

Either way, you will need to prepare the device to run Android apps for development.

Using a physical device

If you have a physical Android device, you can use it for development in place of an AVD by plugging it in to your computer using a USB cable and following the instructions here.

Using a virtual device

If you use Android Studio to open ./AwesomeProject/android, you can see the list of available Android Virtual Devices (AVDs) by opening the “AVD Manager” from within Android Studio. Look for an icon that looks like this:

Android Studio AVD Manager

If you have recently installed Android Studio, you will likely need to create a new AVD. Select “Create Virtual Device…”, then pick any Phone from the list and click “Next”, then select the Q API Level 29 image.

If you don’t have HAXM installed, click on “Install HAXM” or follow these instructions to set it up, then go back to the AVD Manager.

Click “Next” then “Finish” to create your AVD. At this point you should be able to click on the green triangle button next to your AVD to launch it, then proceed to the next step.

Running your React Native application

Step 1: Start Metro

First, you will need to start Metro, the JavaScript bundler that ships with React Native. Metro “takes in an entry file and various options, and returns a single JavaScript file that includes all your code and its dependencies.”—Metro Docs

To start Metro, run npx react-native start inside your React Native project folder:

npx react-native start

react-native start starts Metro Bundler.

If you use the Yarn package manager, you can use yarn instead of npx when running React Native commands inside an existing project.

Step 2: Start your application

Let Metro Bundler run in its own terminal. Open a new terminal inside your React Native project folder. Run the following:

npx react-native run-android

If everything is set up correctly, you should see your new app running in your Android emulator shortly.

npx react-native run-android is one way to run your app – you can also run it directly from within Android Studio.

Watch the below video to learn creating Native app with React Native CLI👇

React Native project structure

Here’s how the typical project structure looks like:

Modifying your app

Now that you have successfully run the app, let’s modify it.

  • Open App.js in your text editor of choice and edit some lines.
  • Press the R key twice or select Reload from the Developer Menu (Ctrl + M) to see your changes!

For example as shown in the last few minutes of above video guide👆

That’s it!

Congratulations! You’ve successfully run and modified your first React Native app.

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