expo-modules-core

What is expo-modules-core?

The expo-modules-core package is a core library for Expo modules, providing essential utilities and base classes for building and integrating native modules in Expo and React Native applications. It helps in creating consistent and efficient modules that can be used across different platforms.

What are expo-modules-core's main functionalities?

Module Registry

The Module Registry feature allows you to access native modules registered in the Expo environment. This example demonstrates how to import and use a native module called 'MyModule' to perform an action.

import { NativeModulesProxy } from 'expo-modules-core';

const { MyModule } = NativeModulesProxy;

MyModule.doSomething();

Event Emitters

Event Emitters in expo-modules-core enable you to listen to and handle events emitted by native modules. This example shows how to create an event emitter for a module and add a listener for a specific event.

import { EventEmitter } from 'expo-modules-core';

const emitter = new EventEmitter(MyModule);

emitter.addListener('eventName', (event) => {
  console.log(event);
});

Platform-specific Code

The Platform module allows you to write platform-specific code by checking the operating system at runtime. This example demonstrates how to log different messages based on whether the app is running on iOS or Android.

import { Platform } from 'expo-modules-core';

if (Platform.OS === 'ios') {
  console.log('Running on iOS');
} else if (Platform.OS === 'android') {
  console.log('Running on Android');
}

Other packages similar to expo-modules-core

react-native

React Native is a popular framework for building mobile applications using JavaScript and React. It provides a set of core components and APIs for building cross-platform apps. Compared to expo-modules-core, React Native offers a broader range of functionalities but requires more setup and configuration for native modules.

react-native-device-info

react-native-device-info is a library that provides device information for React Native apps. It offers functionalities similar to the Platform module in expo-modules-core but focuses specifically on retrieving device-related information such as device model, OS version, and more.

react-native-event-listeners

react-native-event-listeners is a library for managing event listeners in React Native applications. It provides similar functionality to the EventEmitter in expo-modules-core, allowing you to add and remove event listeners easily.

README

The core of Expo Modules architecture.

Installation in managed Expo projects

For managed Expo projects, please follow the installation instructions in the API documentation for the latest stable release. If you follow the link and there is no documentation available then this library is not yet usable within managed projects — it is likely to be included in an upcoming Expo SDK release.

Installation in bare React Native projects

For bare React Native projects, you must ensure that you have installed and configured the expo package before continuing.

Add the package to your npm dependencies

npm install expo-modules-core

Configure for iOS

Run npx pod-install after installing the npm package.

Configure for Android

No additional set up necessary.

Importing native dependencies - autolinking

Many React Native libraries come with platform-specific (native) code. This native code has to be linked into the project and, in some cases, configured further. These actions require some modifications to the native project files. One of the steps that has to be done with the native configuration is to enable the autolinking mechanism that takes care of including any supported module's native code into the project. The following configuration is required:

iOS

Caution! After you have made the following changes you will need to run pod install again.

# Podfile

require File.join(File.dirname(`node --print "require.resolve('react-native/package.json')"`), "scripts/react_native_pods")
require File.join(File.dirname(`node --print "require.resolve('expo-modules-core/package.json')"`), "cocoapods.rb")
require File.join(File.dirname(`node --print "require.resolve('expo-modules-core/package.json')"`), "scripts/autolinking")

#  ...

target "TargetName" do
  use_unimodules!
  config = use_native_modules!
  use_react_native!(:path => config["reactNativePath"])

  # ...
end

Android

// app/build.gradle

apply from: new File(["node", "--print", "require.resolve('expo-modules-core/package.json')"].execute(null, rootDir).text.trim(), "../gradle.groovy")
apply from: new File(["node", "--print", "require.resolve('react-native/package.json')"].execute(null, rootDir).text.trim(), "../react.gradle")
apply from: new File(["node", "--print", "require.resolve('expo-updates/package.json')"].execute(null, rootDir).text.trim(), "../scripts/create-manifest-android.gradle")

// ...

apply from: new File(["node", "--print", "require.resolve('@react-native-community/cli-platform-android/package.json')"].execute(null, rootDir).text.trim(), "../native_modules.gradle");
applyNativeModulesAppBuildGradle(project)

// settings.gradle

apply from: new File(["node", "--print", "require.resolve('expo-modules-core/package.json')"].execute(null, rootDir).text.trim(), "../gradle.groovy");
includeUnimodulesProjects()

apply from: new File(["node", "--print", "require.resolve('@react-native-community/cli-platform-android/package.json')"].execute(null, rootDir).text.trim(), "../native_modules.gradle");
applyNativeModulesSettingsGradle(settings)

Explanation

The scripts that are referenced in Gradle and Cocoapods are usually found the related package inside the project's node_modules directory. In the case of monorepos (such as Yarn workspaces) the project directory may not contain node_modules at all; instead, the modules are likely to be located at the root of the repository. In order to ensure that both cases are supported, we take advantage of the Node dependency resolution strategy. We invoke a subprocess that spawns the simple JavaScript snippet that tries to locate the desired npm package containing the script we need.

• On iOS, we use ` ` (backtick) (alternative reference).
• On Android, we use String[]#execute to obtain the results from the subprocess' stdout.

The Node process that is spawned runs require.resolve to obtain the path to a module's package.json(if you look for the module location using solely module name, you'll be given the path to the file pointed by the main attribute from the package.json and we need to know the location of the module's root directory). We then assemble the path to the desired script and execute it.

You can read more about the scripts and libraries used in the examples above in their official READMEs.

Contributing

Contributions are very welcome! Please refer to guidelines described in the contributing guide.