Mobiai Android Device

Android Device Interaction

Expert-level knowledge for interacting with Android devices and emulators via ADB.

When to Use

• Reproducing a bug on an Android emulator or device
• Taking screenshots or capturing logs
• Automating UI interactions for testing
• Managing emulators

Device Setup

Detect Connected Devices

adb devices -l

This shows all connected devices and emulators. Use -s <serial> to target a specific device, or -e for the only running emulator.

Start an Emulator

Use the helper script or run manually:

# List available AVDs
emulator -list-avds

# Start with recommended flags for automation
emulator -avd <avd-name> \
  -no-window \
  -no-audio \
  -no-boot-anim \
  -gpu swiftshader_indirect \
  -no-snapshot-load

Wait for boot to complete:

adb -e wait-for-device
adb -e shell getprop sys.boot_completed  # Returns "1" when ready

Screen Size

adb shell wm size
# Output: Physical size: 1080x2340

UI Inspection — CRITICAL

Always dump the UI before every interaction. This is the most important rule.

Dump UI Hierarchy

adb shell uiautomator dump /sdcard/ui.xml && adb pull /sdcard/ui.xml ./ui-dump.xml

Never cat the full XML — it can be thousands of lines and will blow up your context. Instead, search for the element you need:

# List all visible text elements with their bounds
grep -o 'text="[^"]*"[^/]*bounds="[^"]*"' ./ui-dump.xml

# Search for a specific element by text
grep -o '[^<]*text="Submit"[^/]*' ./ui-dump.xml

# Search by resource-id
grep -o '[^<]*resource-id="[^"]*btn_submit[^"]*"[^/]*' ./ui-dump.xml

# Search by content-desc
grep -o '[^<]*content-desc="[^"]*Close[^"]*"[^/]*' ./ui-dump.xml

Only cat ./ui-dump.xml as a last resort if grep doesn't find what you need.

The XML contains every visible element with:

• text — visible text on the element
• resource-id — programmatic ID (e.g., com.example.app:id/btn_submit)
• content-desc — accessibility label
• bounds="[x1,y1][x2,y2]" — pixel coordinates

To find tap coordinates: center = ((x1+x2)/2, (y1+y2)/2)

Element Targeting Priority

1. Text — most reliable, search for text="Submit"
2. Resource ID — search for resource-id=".*btn_submit"
3. Content description — search for content-desc="Submit button"
4. Coordinates — last resort, computed from bounds

UI Interaction

Tap + Observe Pattern (USE THIS FOR EVERY TAP)

Critical: Every tap MUST be followed by a UI dump AND logcat check in a single command. Dialogs auto-dismiss in 2-3 seconds — if you dump UI separately, the dialog is gone.

adb shell input tap <x> <y> && sleep 1 && adb shell uiautomator dump /sdcard/ui.xml && adb pull /sdcard/ui.xml ./ui-dump.xml && grep -o 'text="[^"]*"[^/]*bounds="[^"]*"' ./ui-dump.xml && echo "=== LOGCAT ===" && adb logcat -d -t 30

Other Interactions

# Back button
adb shell input keyevent 4

# Home button
adb shell input keyevent 3

# Enter/OK
adb shell input keyevent 66

# Delete/Backspace
adb shell input keyevent 67

# Swipe (scroll down)
adb shell input swipe 540 1500 540 500 300

# Long press (swipe with same start/end)
adb shell input swipe <x> <y> <x> <y> 1000

Typing Text

Never use adb shell input text for text that goes into app fields — it triggers an Android "pasted from clipboard" notification that can break the app.

Type digits using keyevents:

Example — type "1234":

adb shell input keyevent 8 9 10 11

For text fields where keyevents won't work (search, filters), use input text as a fallback.

Logcat — Why It Matters More Than UI Dumps

Dialogs, toasts, and error popups auto-dismiss in 2-3 seconds. The UI dump may miss them entirely. But logcat always contains the error message that triggered the popup.

Check for Crashes

# Check for fatal exceptions
adb logcat -d | grep -A 10 "FATAL EXCEPTION"

# Check for ANR (Application Not Responding)
adb logcat -d | grep "ANR in"

# Dump last 50 lines with timestamps
adb logcat -d -t 50

Filter Logcat by App

# Get the app's PID
adb shell pidof com.example.myapp

# Filter by PID
adb logcat -d | grep <pid>

Clear Logcat

adb logcat -c

Always clear logcat before a test sequence to get clean logs.

Screenshots

adb shell screencap -p /sdcard/screenshot.png
adb pull /sdcard/screenshot.png ./screenshot.png
adb shell rm -f /sdcard/screenshot.png

Screen Recording

# Start recording (max 180 seconds per Android limit)
adb shell screenrecord /sdcard/recording.mp4 &

# Stop recording
adb shell pkill -INT screenrecord

# Wait for finalization, then pull
sleep 3
adb pull /sdcard/recording.mp4 ./recording.mp4

For sessions longer than 180s, use segmented recording (start a new segment before the previous one ends).

App Management

# Launch an app
adb shell monkey -p com.example.myapp -c android.intent.category.LAUNCHER 1

# Force stop an app
adb shell am force-stop com.example.myapp

# Clear app data
adb shell pm clear com.example.myapp

# Install APK
adb install -r app-debug.apk

# Install split APKs
adb install-multiple base.apk config.apk

# Grant permissions
adb shell pm grant com.example.myapp android.permission.ACCESS_FINE_LOCATION

Handling Common Issues

"Display over other apps" dialog

adb shell appops set <package> SYSTEM_ALERT_WINDOW allow
adb shell am force-stop com.android.settings

Emulator not responding

adb emu kill  # Graceful kill
# If that fails:
taskkill /F /IM qemu-system-x86_64.exe  # Windows
pkill qemu-system-x86_64                # macOS/Linux

adb server issues

adb kill-server && adb start-server

Wait Times

• After tap: 1-2 seconds (included in the standard tap command)
• After screen transition: 2-3 seconds
• After network call: 3-5 seconds
• After app launch: 5-10 seconds
• After emulator boot: check sys.boot_completed property