Flutter Biometric Finger

A powerful Flutter plugin for integrating NEXT Biometrics USB fingerprint scanners on Android.

This package provides a clean Flutter API for:

• Fingerprint image capture
• ISO template extraction
• Multi finger enrollment
• 1:1 verification flows
• Scanner lifecycle management
• PNG fingerprint preview rendering

Built for production grade biometric enrollment and verification workflows.

---

Features

• USB fingerprint scanner initialization
• ISO compliant fingerprint template extraction
• PNG fingerprint image generation
• Single finger verification
• Multi finger enrollment
• Real time quality metrics
• Finger spoof detection support
• Clean Flutter widget API
• Android native SDK integration using Kotlin
• Automatic SDK binary download during build

---

Supported Hardware

Tested Devices:

Type	Model
NB65200U	AbeTree-ATS-24

---

Platform Support

Platform	Support
Android	✅
iOS	❌
Web	❌
Windows	❌
macOS	❌
Linux	❌

Minimum Android SDK: 24

---

Installation

Add dependency:

dependencies:
  flutter_biometric_finger: ^0.0.1

Run:

flutter pub get

---

Android Configuration

Android 11+ Requirement

Add this attribute inside your AndroidManifest.xml application tag:

<application
    android:name="${applicationName}"
    android:label="your_app_name"
    android:icon="@mipmap/ic_launcher"
    android:allowNativeHeapPointerTagging="false">

This prevents crashes caused by legacy native biometric SDKs on Android 11+ devices.

---

💻 Usage

1. Initialize the Scanner

Before scanning, you must initialize the device.

import 'package:flutter_biomatric_finger/flutter_biomatric_finger.dart';

final scanner = FlutterBiomatricFinger();

final device = await scanner.initialize();

if (!device.found) {
  print("Scanner not found: ${device.message}");
  return;
}

print("Scanner initialized successfully!");

---

2. Scan and Extract Data

Once initialized, prompt the user to place their finger on the scanner and call scanAndExtract().

final scan = await scanner.scanAndExtract();

if (scan.status == 'success') {
  print("Scan Quality: ${scan.quality}");
  print("ISO Template (Base64): ${scan.templateBase64}");
} else {
  print("Scan failed: ${scan.status}");
}

---

3. Display the Fingerprint Image

The plugin automatically converts the raw scanner data into a standard PNG format. You can easily display it using Flutter's Image.memory widget.

if (scan.imagePngBytes != null) {
  Image.memory(scan.imagePngBytes!);
}

---

4. Dispose

Always dispose of the scanner when you are done to release the USB interface and free up memory.

await scanner.dispose();

---

Quick Start

Import package:

import 'package:flutter_biometric_finger/flutter_biometric_finger.dart';

---

Initialize Scanner

final controller = ScannerController();

await controller.initialize();

---

Single Finger Verification

final controller = ScannerController(
  fingers: [Finger.rightThumb],
);

---

Right Hand Enrollment

final controller = ScannerController(
  fingers: Finger.rightHand,
);

---

Custom Finger Selection

final controller = ScannerController(
  fingers: const [
    Finger.rightIndex,
    Finger.leftIndex,
  ],
);

---

Scanner Widget

ScannerWidget(
  controller: controller,
)

---

Scan Callback

ScannerWidget(
  controller: controller,
  onScanComplete: (result) {
    debugPrint(result.templateBase64);
  },
)

---

Full Example

import 'package:flutter/material.dart';
import 'package:flutter_biometric_finger/flutter_biometric_finger.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: ScannerPage(),
    );
  }
}

class ScannerPage extends StatefulWidget {
  const ScannerPage({super.key});

  @override
  State<ScannerPage> createState() => _ScannerPageState();
}

class _ScannerPageState extends State<ScannerPage> {
  late final ScannerController controller;

  @override
  void initState() {
    super.initState();

    controller = ScannerController(
      fingers: [Finger.rightThumb],
    );
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Fingerprint Scanner')),
      body: ScannerWidget(
        controller: controller,
        onScanComplete: (result) {
          debugPrint(
            'Template length: ${result.templateBase64.length}',
          );
        },
      ),
    );
  }
}

---

Scan Result

Each completed scan returns:

result.templateBase64
result.imagePngBytes
result.quality
result.finger
result.spoofScore
result.scanMillis

---

Finger Presets

Available presets:

Finger.rightThumb
Finger.leftThumb
Finger.rightHand
Finger.leftHand
Finger.all

Or custom selection:

[
  Finger.rightIndex,
  Finger.leftIndex,
]

---

Example App

The package includes a fully functional example application demonstrating:

• All 10 finger capture
• Single finger verification
• Right hand enrollment
• Custom subset scanning
• Fingerprint preview rendering
• ISO template extraction

Run example:

cd example
flutter run

---

Troubleshooting

Scanner Not Found

Check:

• USB OTG is enabled
• Scanner is connected properly
• USB permission was granted

---

App Crashes During Scan

Verify:

android:allowNativeHeapPointerTagging="false"

is added inside the application tag.

---

Unsupported Device

Currently tested only with:

• NB65200U
• AbeTree-ATS-24

Other NEXT Biometrics devices may work but are not officially verified.

---

Architecture

This plugin uses:

• Flutter MethodChannel
• Native Android Kotlin integration
• AbeTree / NEXT Biometrics Android SDK
• USB host communication
• ISO fingerprint template extraction

---

License

BSD 3-Clause License