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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.
  • 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.

Standalone Apps

If you don't need custom native code outside of the Expo SDK, head over to our documentation on building standalone apps without needing Android Studio and Xcode.

If you need standalone apps as built by running expo build:ios or expo build:android for a supported SDK version, check out our docs on using turtle-cli to build apps locally or on CI.

If you're still here, you need to build a standalone app with code currently on main or another unreleased branch. Make sure to follow the Configure app.json section of the docs before continuing. You'll need to add the appropriate fields to your app.json before the standalone app scripts can run. Once that's done, continue on to the platform-specific instructions.

Android

The Android standalone app script creates a new directory android-shell-app with the modified Android project in it. It then compiles that new directory giving you a signed or unsigned .apk depending on whether you provide a keystore and the necessary passwords. If there are issues with the app you can open the android-shell-app project in Android Studio to debug.

Here are the steps to build a standalone Android app:

  • Publish your experience with Expo CLI. Note the published URL.
  • If you want a signed .apk, run et android-shell-app --url [the published experience url] --sdkVersion [sdk version of your experience] --keystore [path to keystore] --alias [keystore alias] --keystorePassword [keystore password] --keyPassword [key password].
  • If you don't want a signed .apk, run et android-shell-app --url [the published experience url] --sdkVersion [sdk version of your experience].
  • The .apk file will be at /tmp/shell-signed.apk for a signed .apk or at /tmp/shell-debug.apk for an unsigned .apk.

iOS

The iOS standalone app script has two actions, build and configure:

  • build creates an archive or a simulator build of the Expo iOS workspace,
  • configure accepts a path to an existing archive and modifies all its configuration files so that it will run as a standalone Expo project rather than in Expo Go.

Here are the steps to build a standalone iOS app:

  • Publish your experience with Expo CLI. Note the published URL.
  • et ios-shell-app --action build --type [simulator or archive] --configuration [Debug or Release]
  • The resulting archive will be created at ../shellAppBase-[type].
  • et ios-shell-app --url [the published experience url] --action configure --type [simulator or archive] --archivePath [path to ExpoKitApp.app] --sdkVersion [sdk version of your experience] --output your-app.tar.gz
  • This bundle is not signed and cannot be submitted to iTunes Connect as-is; you'll need to manually sign it if you'd like to submit it to Apple. Fastlane is a good option for this. Also, Expo will do this for you if you don't need to build this project from source.
  • If you created a simulator build in the first step, unpack the tar.gz using tar -xvzf your-app.tar.gz. Then you can run this on iPhone Simulator using xcrun simctl install booted <app path> and xcrun simctl launch booted <app identifier>. Another alternative which some people prefer is to install the ios-sim tool and then use ios-sim launch <app path>.
  • There are a few more optional flags you can pass to this script. They are all documented in the block comments inside xdl/src/detach/IosShellApp.js.

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 expo start 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.