Android Emulator Debug

2. Launch the Emulator (Headed)

Always launch with a visible window so the user can interact. Use & and disown so the process doesn't block.

export ANDROID_AVD_HOME=/home/shakdwipeea/.config/.android/avd
$HOME/Android/Sdk/emulator/emulator -avd Pixel_6_API_34 -gpu swiftshader_indirect &>/tmp/emulator.log &
disown
echo "Emulator launched"

Wait for boot — poll in a loop with a timeout (never use a blocking adb wait-for-device without a timeout guard):

for i in $(seq 1 30); do
  boot=$(adb shell getprop sys.boot_completed 2>/dev/null | tr -d '\r')
  if [ "$boot" = "1" ]; then
    echo "BOOTED after ~$((i*3))s"
    adb devices
    exit 0
  fi
  sleep 3
done
echo "TIMEOUT"

Verify the process is alive before polling:

pgrep -f "qemu-system" >/dev/null && echo "Emulator process running" || echo "NOT running"

3. Build the APK

Build via Gradle directly — do not use npm run android or expo run:android as they start Metro in a blocking foreground process.

cd apps/mobile/android
JAVA_HOME=/usr/lib/jvm/java-17-openjdk ./gradlew assembleDebug 2>&1 | tail -20

The APK lands at: apps/mobile/android/app/build/outputs/apk/debug/app-debug.apk

If the APK already exists and no native dependencies changed, skip the build.

4. Install the APK

adb install -r apps/mobile/android/app/build/outputs/apk/debug/app-debug.apk 2>&1

5. Start Metro Bundler

Start in background with disown. Use a timeout on the command that waits for readiness.

cd apps/mobile
npx expo start --port 8081 --localhost &>/tmp/metro.log &
disown
sleep 10
curl -s http://localhost:8081/status  # expect: packager-status:running

6. Set Up adb Reverse Proxy

Required — the emulator can't reach the host's localhost without this:

adb reverse tcp:8081 tcp:8081

Without this, the app shows "Unable to load script".

7. Launch the App

adb shell am force-stop com.sumitnarang76.bookmarksmobile
sleep 1
adb shell am start -n com.sumitnarang76.bookmarksmobile/.MainActivity 2>&1

Allow 15-20 seconds for the JS bundle to load on first launch.

8. Take Screenshots

adb exec-out screencap -p > /tmp/screenshot.png

Then use the read tool to view: read /tmp/screenshot.png

Image coordinate mapping: Screenshots report "displayed at WxH. Multiply coordinates by N to map to original image." Always multiply display coordinates by the given factor when computing tap targets.

9. Read Logcat for Errors

# Recent React Native errors
adb logcat -d | grep "ReactNativeJS" | grep -iE "error|warn" | tail -20

# Full recent log (last 100 lines)
adb logcat -d -t 100 | grep -iE "ReactNative|ExpoModules|error|fatal" | tail -30

# Clear and watch for fresh errors after reproducing
adb logcat -c
# ... reproduce the issue ...
adb logcat -d | grep "ReactNativeJS" | tail -20

10. Simulate User Input

# Tap at pixel coordinates (original image coordinates)
adb shell input tap <x> <y>

# Android system back button
adb shell input keyevent KEYCODE_BACK

# Type text
adb shell input text "hello"

# Swipe (x1 y1 x2 y2 duration_ms)
adb shell input swipe 540 1800 540 600 300

Tap Coordinate Tips

• Get the status bar height (touch targets are offset by this):

  adb shell dumpsys window StatusBar 2>/dev/null | grep "frame=" | head -1
  

  Typical value: 128px on Pixel 6 API 34.
• Safe-area content starts below the status bar. A button at visual y=50 in the screenshot is likely untappable — it's behind the system UI.
• Use adb shell input keyevent KEYCODE_BACK as a reliable alternative to tapping custom back buttons.

Teardown

# Kill emulator
pkill -f "qemu-system" 2>/dev/null

# Kill Metro
pkill -f "expo.*start" 2>/dev/null
pkill -f "@expo/cli" 2>/dev/null

# Kill adb server
adb kill-server 2>/dev/null

Quick Full Workflow

# 1. Launch emulator
export ANDROID_AVD_HOME=/home/shakdwipeea/.config/.android/avd
$HOME/Android/Sdk/emulator/emulator -avd Pixel_6_API_34 -gpu swiftshader_indirect &>/tmp/emulator.log &
disown

# 2. Wait for boot
for i in $(seq 1 30); do
  [ "$(adb shell getprop sys.boot_completed 2>/dev/null | tr -d '\r')" = "1" ] && break; sleep 3
done

# 3. Build + install (skip build if APK exists and no native changes)
cd apps/mobile/android && JAVA_HOME=/usr/lib/jvm/java-17-openjdk ./gradlew assembleDebug 2>&1 | tail -5
adb install -r app/build/outputs/apk/debug/app-debug.apk

# 4. Start Metro
cd .. && npx expo start --port 8081 --localhost &>/tmp/metro.log & disown
sleep 10

# 5. Reverse proxy + launch
adb reverse tcp:8081 tcp:8081
adb shell am force-stop com.sumitnarang76.bookmarksmobile
adb shell am start -n com.sumitnarang76.bookmarksmobile/.MainActivity

# 6. Screenshot after bundle loads
sleep 20
adb exec-out screencap -p > /tmp/screenshot.png

Common Pitfalls