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Developing Expo Go.md

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Developing Expo Go

Introduction

This is the source code for the Expo Go app used to view projects published to the Expo service. If you want to build and install Expo Go directly onto a device, you're in the right place. Note that if you just want to install Expo Go on a simulator, you do not need to build it from source. Instead, you should follow the instructions here.

To build Expo Go, follow the instructions in the Setup section below. Use the Expo CLI to use Expo's infrastructure to build your app.

Please ask us on the forums if you get stuck.

External Contributions

Please check with us before putting work into a Pull Request! We don't yet have a good guide available that covers the nuances of how to work with Expo Go and the types of PRs that we accept, so you will want a direct line of communication with someone on the team to ask us questions. The best place to talk to us is either on Discord at https://chat.expo.dev or the forums at https://forums.expo.dev.

Disclaimers:

If you want to build a standalone app that has a custom icon and name, see our documentation here. You're in the wrong place and you shouldn't need to build Expo Go from source.

If you need to make native code changes to your Expo project, such as adding custom native modules, we can generate a native project for you. You're in the wrong place and you shouldn't need to build Expo Go from source.

Configuring your environment

Note: We support building Expo Go only on macOS.

  • Install direnv.
  • Clone this repo; we recommend cloning it to a directory whose full path does not include any spaces (you should clone all the submodules with git clone --recurse-submodules).
  • Run yarn in the root directory.
  • Run yarn setup:native in the root directory.
  • Run yarn build in the packages/expo directory.

iOS

  • Make sure you have latest non-beta Xcode installed.
  • Run et ios-generate-dynamic-macros.
  • Open and run ios/Exponent.xcworkspace in Xcode.

Android

Running on a Device

iOS

  • In Xcode's menu bar, open the Xcode drop-down menu, and select Preferences. Then in the Accounts tab of the preferences menu, add your personal or team Apple Developer account.
  • Connect your test device to your computer with a USB cable.
  • In Xcode's menu bar, open the Product drop-down menu, select Destination, then in the Device grouping select your device.
  • In the project navigator, select the Exponent project to bring up the project's settings, and then:
    • In the General tab, in the Identity section, put in a unique Bundle Identifier.
    • Also in the General tab, in the Signing section, select your personal or team Apple Developer account as your Team, and create a new signing certificate by clicking Fix Issue.
  • In the project's settings page, select the ExpoNotificationServiceExtension target, and then:
    • In the General tab, in the Identity section, change its Bundle Identifier to be prefixed with your unique Bundle Identifier. For example, if your unique Bundle Identifier is host.exp.Exponent.unique, then the Bundle Identifier for the notification service extension should be host.exp.Exponent.unique.ExpoNotificationServiceExtension.
  • Finally, run the build.

Android

  • If the Play Store version of the Expo Go is installed on your test device, uninstall it.
  • Connect your test device to your computer with a USB cable.
  • Run fastlane android start, or alternately open the android directory in Android Studio, start it, and in the Select Deployment Target dialog, select your device.
    • Expo Go can be built with either versioned or unversioned flavor. The latter is highly recommended for development and is used by default in Android Studio. You can switch flavors in Build Variants pane.
    • You can also run ./gradlew installUnversionedDebug from the android directory.
    • If you're having trouble building the Android app, trying clearing your gradle cache with ./gradlew clean and rebuilding.

Modifying JS Code

The Expo Go apps run a root Expo project in addition to native code. By default, this will use a published version of the project, so any changes made in the home directory will not show up without some extra work.

Serve this project locally by running npx expo start --port=80 from the home directory. On iOS, you'll additionally need to set DEV_KERNEL_SOURCE to LOCAL in EXBuildConstants.plist (the default is PUBLISHED).

The native Android Studio and Xcode projects have a build hook which will find this if expo start is running. Keep this running and rebuild the app on each platform.

Tests

iOS

For native XCTest unit tests:

  • Press Command+U in XCode to build and test the Tests unit test target.
  • Alternatively, run fastlane ios test from the parent directory of ios.

For JS integration tests, test the ExponentIntegrationTests target (not included in the default test scheme). This target requires you to configure EXTestEnvironment.plist with a key testSuiteUrl whose value is the URL to load some version of Expo's test-suite app. This will run a bunch of Jasmine tests against the Expo SDK.