Android Basics for RN Devs

Android Studio, adb, and Gradle - the minimum native Android literacy every React Native developer needs without becoming a full-time Android engineer. On Expo SDK 57 you spend most days in JavaScript; this page is the map for when builds break, permissions misbehave, or Play Console asks questions Gradle can answer.

Recipe

Quick-reference recipe card - copy-paste ready.

# Verify toolchain before any native build
java -version          # expect 17.x (Temurin or Android Studio bundled JDK)
echo $ANDROID_HOME     # ~/Library/Android/sdk on macOS default install
 
# List devices and start Metro-backed debug build
adb devices
npx expo run:android
 
# Tail React Native + app logs (filter noise)
adb logcat '*:S' ReactNative:V ReactNativeJS:V AndroidRuntime:E
 
# Reverse Metro port when USB debugging (Wi-Fi dev client uses LAN IP instead)
adb reverse tcp:8081 tcp:8081
 
# Regenerate android/ from app.config (CNG workflow)
npx expo prebuild --platform android

android/                          # generated by prebuild - treat as build output in CNG
├── settings.gradle               # includes app module + autolinked native libs
├── build.gradle                  # root project plugins (AGP, Kotlin)
├── gradle.properties             # JVM args, New Arch flags, caching toggles
└── app/
    ├── build.gradle              # applicationId, SDK versions, dependencies, signing
    └── src/main/
        ├── AndroidManifest.xml   # permissions, intent filters (from app.config)
        └── java/.../MainActivity.kt

When to reach for this:

• First npx expo run:android fails with JDK or SDK path errors.
• You need logcat to debug a native crash that never reaches the JS redbox.
• A teammate asks why android/ exists and whether to commit it.
• You are tracing where a manifest permission or Gradle dependency came from.

Working Example

Step 1 - Confirm environment

# macOS - typical Android Studio install paths
export ANDROID_HOME="$HOME/Library/Android/sdk"
export PATH="$PATH:$ANDROID_HOME/platform-tools:$ANDROID_HOME/emulator"
 
# Expo SDK 57 / RN 0.86 expects JDK 17
/usr/libexec/java_home -V
export JAVA_HOME=$(/usr/libexec/java_home -v 17)
 
npx expo-doctor

Step 2 - Run on emulator or USB device

# Start a recent API image (API 34–35) - not API 28 museum pieces
emulator -list-avds
emulator -avd Pixel_8_API_35 &
 
adb wait-for-device
npx expo run:android

Step 3 - Debug a white screen

# Terminal 1 - Metro already started by run:android; or:
npx expo start --dev-client
 
# Terminal 2 - native + JS logs
adb logcat '*:S' ReactNativeJS:V ReactNative:V SoLoader:E AndroidRuntime:E

Step 4 - Install a CI/EAS APK locally

adb install -r ./build.apk
adb shell am start -n com.example.shopapp/.MainActivity

What this demonstrates:

• adb devices - one authorized device/emulator before Gradle deploys.
• adb reverse - USB device reaches Metro on localhost:8081.
• logcat filters - surface JS console.log and native stack traces.
• android/ layout - know which file to inspect vs which to regenerate with prebuild.

Deep Dive

How It Works

• Expo CNG (Continuous Native Generation) generates android/ from app.config.ts + config plugins. You edit config, not hand-merge build.gradle on every upgrade.
• npx expo run:android invokes Gradle (:app:installDebug), installs the debug APK, and launches the dev client or debug build.
• Autolinking (via expo-modules-autolinking) injects native modules into settings.gradle - you do not manually include each library.
• Android Studio is for inspecting layouts, profiling, and editing Kotlin when you ship custom native code - not for daily JS iteration.
• adb bridges host machine and device: shell, file push/pull, intents, port forwarding.

Gradle Mental Model

// app/build.gradle (simplified mental model - actual file is prebuild-generated)
android {
    namespace "com.example.shopapp"
    defaultConfig {
        applicationId "com.example.shopapp"
        minSdkVersion rootProject.ext.minSdkVersion
        targetSdkVersion rootProject.ext.targetSdkVersion
    }
}
dependencies {
    implementation("com.facebook.react:react-android")
    // autolinked Expo modules appear here after prebuild
}

Android Studio Essentials

You do not need Android Studio running for npx expo run:android - only the SDK + platform-tools on PATH.

adb Commands RN Devs Use Weekly

CNG vs Committed android/

SDK 57 teams usually gitignore android/ and regenerate - see Prebuild Basics.

Gotchas

• Wrong JDK version - AGP 8.x requires JDK 17; JDK 8 or 21 mismatches produce opaque "Could not resolve" errors. Fix: export JAVA_HOME to 17 before Gradle.
• ANDROID_HOME unset - sdkmanager and Gradle cannot find build-tools. Fix: Point at Android Studio SDK path; add platform-tools to PATH.
• Editing android/ without a plugin - Next prebuild --clean wipes manual edits. Fix: Move changes to a config plugin or expo-build-properties.
• Ancient emulator API level - API 24 emulators hide edge-to-edge, photo picker, and permission changes in RN 0.86. Fix: Test on API 34–35 images.
• adb device unauthorized - RSA fingerprint not accepted on phone. Fix: Revoke USB debugging authorizations on device; replug and accept prompt.
• Assuming Android Studio Run ▶ replaces Expo - Studio builds its own variant; Metro may not attach. Fix: Use npx expo run:android for dev-client workflow.

Alternatives

FAQs

Related

• Edge-to-Edge on Android - RN 0.86 system bar behavior
• Gradle Performance & Caching - faster local and EAS builds
• Permissions & Play Policy - runtime permissions and manifest
• ../deep-linking/android-app-links/android-app-links.md - intent filters and adb verification
• ../cng-prebuild/prebuild-basics/prebuild-basics.md - when android/ is generated
• ../cli/adb-and-android-devices/adb-and-android-devices.md - extended adb recipes

Stack versions: This page was written for React 19.2.3, React Native 0.86.0, and Expo SDK 57 (expo ~57.0.4).