Zebra Price Label

Android app for printing price labels to a USB-connected Zebra ZD410 printer.

Features

• Enter a price on a numeric keypad
• Choose label size (25×13 mm, 46.8×81 mm, 50.8×25.4 mm)
• Print ZPL labels with centered price and black pill styling (small label)
• Fine-tune print position per label size (saved permanently)
• USB Zebra printer discovery and printing

Requirements

• Node.js ≥ 22.11
• Android SDK and a connected device or emulator
• Zebra ZD410 (or compatible ZPL USB printer)

Development

npm install
npm start
npm run android

In one terminal, keep Metro running (npm start). In another, build and launch the app (npm run android).

Android emulator

1. Open Android Studio → Device Manager and start a virtual device (or run emulator -list-avds then emulator -avd <name>).
2. With Metro running, install and launch the app:

npm run android

The emulator can exercise the UI, but it has no USB host access — printer discovery and printing require a physical device.

Physical device over Wi‑Fi

Useful when the tablet/phone stays on the desk and you do not want a USB cable for Metro/adb. USB printing still needs the OTG cable to the Zebra printer.

One-time setup (device on the same Wi‑Fi as your PC):

1. Enable Developer options and USB debugging on the device.
2. Connect the device with USB and confirm it appears in adb devices.
3. Switch adb to TCP/IP mode:

adb tcpip 5555

4. Find the device IP (Wi‑Fi settings, or adb shell ip route | awk '{print $9}').
5. Connect over the network:

adb connect <device-ip>:5555
adb devices

You should see <device-ip>:5555 listed. You can unplug USB.

Daily dev:

npm start
npm run android

If the wireless adb connection drops (sleep, reboot, network change), repeat from adb connect <device-ip>:5555. On Android 11+, you can also pair from Developer options → Wireless debugging if adb tcpip is unavailable.

Build release APK

npm run build:apk

Output: dist/ZebraLabel-<version>-release.apk

Local release signing

Copy android/keystore.properties.example to android/keystore.properties and fill in your passwords. The keystore file lives at the repo root (zebra-label-release.keystore, gitignored). Without keystore.properties, release builds fall back to the debug keystore.

GitHub Actions signing

Add these repository secrets (Settings → Secrets and variables → Actions):

Secret	Value
ANDROID_KEYSTORE_BASE64	Base64 of zebra-label-release.keystore (see below)
ANDROID_KEYSTORE_PASSWORD	Keystore password
ANDROID_KEY_ALIAS	zebra-label
ANDROID_KEY_PASSWORD	Key password

Encode the keystore (Git Bash / Linux / macOS):

base64 -w 0 zebra-label-release.keystore

PowerShell:

[Convert]::ToBase64String([IO.File]::ReadAllBytes("zebra-label-release.keystore"))

Paste the single-line output into ANDROID_KEYSTORE_BASE64. Release tags and pushes to main build a Play Store–compatible signed APK; pull requests still use the debug keystore so forks do not need secrets.

Install over Wi‑Fi (adb)

Set up wireless adb once as in Physical device over Wi‑Fi, then install or update the release APK without USB:

adb connect <device-ip>:5555
adb install -r dist/ZebraLabel-<version>-release.apk

-r replaces an existing install. If adb lists multiple devices, target the tablet explicitly:

adb -s <device-ip>:5555 install -r dist/ZebraLabel-<version>-release.apk

Replace <version> with the version from package.json (e.g. 0.0.1). If the connection dropped, run adb connect <device-ip>:5555 again before installing.

Test CI locally with act

Run the GitHub Actions workflow locally with act. The --artifact-server-path flag is required so upload-artifact can store the built APK under .artifacts/:

act workflow_dispatch -W .github/workflows/build-apk.yml -j build-apk --artifact-server-path .artifacts

On the first run, Cache not found for input keys: Linux-android-ndk-… is normal — nothing has been saved yet. The NDK is downloaded by sdkmanager, then cached at the end of the job.

Important: actions/cache only saves when the job succeeds (post-if: success()). If a previous local run failed (for example at upload-artifact without --artifact-server-path), the NDK cache was never written and the next run will miss again. Gradle caches may still restore because setup-gradle saves independently. Once a run completes successfully, subsequent runs should restore the NDK cache.

Capture a screenshot for the README

Update the Owl baseline (used in the README image above):

npm run owl:test:android:update

This writes .owl/baseline/android/home-screen.png.

Project layout

Path	Purpose
App.tsx	App entry (safe area wrapper)
src/components/AppContent.tsx	Main UI
src/buildZpl.ts	ZPL label templates
src/labelOffsetStorage.ts	Persistent position offsets
android/.../ZebraPrinterModule.kt	USB print native module
scripts/build-apk.js	Release APK build script

Misc

keystore creation: keytool -genkeypair -v -storetype PKCS12 -keystore zebra-label-release.keystore -alias zebra-label -keyalg RSA -keysize 2048 -validity 10000 -dname "CN=Zebra Label, OU=Development, O=Seb Green, L=Dresden, ST=Saxony, C=DE, EMAILADDRESS=sebgreenbus@gmail.com"