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A Bit Above Bytes
A Bit Above Bytes

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I Built a 21K-Line Android Scanner App in One Day — Here's the Full Template

#android #jetpackcompose #kotlin #mobile

Every document scanner app on the Play Store looks the same. They all use CameraX, ML Kit, and Room — yet developers keep rebuilding the same architecture from scratch.

So I built the template once, properly, and I'm sharing the full source.

What's Inside

92 Kotlin files. 21,000+ lines. Production-ready architecture.

  • Scanner Engine — CameraX + ML Kit Document Scanner with auto-capture, frame stability detection, 6 scan modes (Document, ID Card, Passport, Receipt, Whiteboard, Book)
  • PDF Engine — Generate, merge, split PDFs with invisible OCR text layer at 300 DPI. No iText dependency (avoids AGPL licensing headaches)
  • OCR — ML Kit Text Recognition v2 with bounding box positioning, background processing via WorkManager
  • eSign — Draw, type, or upload signatures. Composite onto document pages
  • Monetization — RevenueCat integration with metered paywall (soft prompt at scan 2, hard gate at limit), 4 A/B test paywall variants, weekly + annual plans
  • Full UI — Material 3 + Jetpack Compose. Dark onboarding flow, animated paywall, bottom navigation, document grid/list views

Architecture 

data/          → Room DB (5 entities, 5 DAOs), Repository pattern, DataStore prefs
domain/        → Use cases, engine layer (Scan, PDF, OCR, eSign, Barcode)
ui/            → 15+ screens, Compose navigation, Hilt DI
service/       → WorkManager workers for background OCR + PDF export
util/          → Analytics, RevenueCat config, A/B testing via Firebase Remote Config
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Clean Architecture with proper separation. Not a tutorial project — this is what you'd actually ship.

The Stack

Layer Tech
Language Kotlin 2.0
UI Jetpack Compose + Material 3
Camera CameraX 1.4
ML ML Kit (Document Scanner, Text Recognition, Barcode)
Database Room 2.6
DI Hilt
Payments RevenueCat
Analytics Firebase Analytics + Crashlytics + Remote Config
Background WorkManager
Security AES-256-GCM encryption, Biometric lock

Why I Built This

I kept seeing the same pattern: developers spend 2-3 months building scanner app infrastructure before they can even start on their unique features. Edge detection, perspective correction, OCR positioning, PDF generation with text layers, paywall flows — it's all solved problems, but the implementation details eat your time alive.

This template handles the 80% that's identical across every scanner app, so you can focus on what makes yours different.

What You Can Build With It

  • Receipt scanner for expense tracking
  • Business card scanner with CRM integration
  • Medical document organizer
  • Construction site documentation tool
  • Legal document management app
  • Student note digitizer

Rebrand it, customize the UI, add your domain-specific features, and ship.

Get It

The full template is available here: ScanVault Pro Template on Gumroad

Includes complete source code, architecture docs, customization guide, and a quick-start walkthrough.

Happy to answer any questions about the architecture decisions or implementation details in the comments.

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