LPAPI Thermal Printer Plugin #

A Flutter plugin for Dothantech thermal label printers that provides seamless Bluetooth connectivity and printing capabilities. This plugin supports direct printer discovery without requiring manual Bluetooth pairing, making it ideal for warehouse and retail applications.

Features #

• 🔍 Bluetooth Discovery: Find printers without manual pairing
• 🔗 Direct Connection: Connect to printers instantly
• 📝 Text Printing: Print plain text with customizable formatting
• 📊 Barcode Support: Generate and print 1D barcodes
• 📱 QR Codes: Create and print 2D QR codes
• 🖼️ Image Printing: Print images from base64 data
• ⚙️ Print Settings: Adjustable density and speed
• 📱 Android Support: Full support for Android devices
• 🍎 iOS Support: Full support for iOS devices

Supported Printers #

This plugin works with Dothantech thermal label printers using the LPAPI SDK, including:

• Bluetooth thermal label printers
• Mobile receipt printers
• Portable label printers

Tested Devices #

This plugin has been tested and verified to work with:

• P1 Series Label Printer - Full functionality confirmed including Bluetooth discovery, connection, and all printing features

P1 Series Printer Features

• Bluetooth Connectivity: Seamless wireless connection without manual pairing
• Label Sizes: Supports various label dimensions (tested with 48mm x 50mm labels)
• Print Quality: Adjustable density (0-20) and speed (1-5) settings
• Barcode Support: 1D barcodes with optional text labels
• QR Code Support: 2D QR codes for product tracking and information
• Image Printing: Base64 encoded image support for logos and graphics

Installation #

Add this to your package's pubspec.yaml file:

dependencies:
  flutter_dothantech_lpapi_thermal_printer: ^1.0.0

Then run:

flutter pub get

Platform Setup #

Android #

Permissions

Add the following permissions to your android/app/src/main/AndroidManifest.xml:

<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

MinSDK Version

Ensure your android/app/build.gradle has:

android {
    compileSdkVersion 33

    defaultConfig {
        minSdkVersion 21
        targetSdkVersion 33
    }
}

iOS #

Permissions

Add the following to your ios/Runner/Info.plist:

<key>NSBluetoothAlwaysUsageDescription</key>
<string>This app needs Bluetooth access to connect to thermal printers</string>
<key>NSBluetoothPeripheralUsageDescription</key>
<string>This app needs Bluetooth access to connect to thermal printers</string>

Deployment Target

Ensure your iOS deployment target is at least 12.0. Update ios/Podfile:

platform :ios, '12.0'

Usage #

Import the package #

import 'package:flutter_dothantech_lpapi_thermal_printer/flutter_dothantech_lpapi_thermal_printer.dart';

Initialize the printer #

final printer = LpapiThermalPrinter();

Request Permissions #

Android

For Android 12+ (API 31+), you need to request Bluetooth permissions at runtime:

import 'package:permission_handler/permission_handler.dart';

Future<void> requestPermissions() async {
  if (Platform.isAndroid) {
    Map<Permission, PermissionStatus> statuses = await [
      Permission.bluetooth,
      Permission.bluetoothScan,
      Permission.bluetoothConnect,
      Permission.location,
    ].request();

    if (!statuses.values.every((status) => status.isGranted)) {
      print('Please grant all permissions to use the printer');
    }
  } else if (Platform.isIOS) {
    // iOS will automatically request Bluetooth permissions when scanning
    // No additional runtime permissions needed if Info.plist is configured
  }
}

Discover Printers #

Find all nearby printers (including unpaired):

List<PrinterInfo> printers = await printer.discoverPrinters();
for (var p in printers) {
  print('Found printer: ${p.name} at ${p.address}');
}

Find only paired printers:

List<PrinterInfo> pairedPrinters = await printer.searchPrinters();

Connect to a Printer #

Connect to a specific printer:

bool connected = await printer.connectPrinter('00:11:22:33:44:55');
if (connected) {
  print('Connected successfully!');
}

Quick connect to first available printer:

bool connected = await printer.connectFirstPrinter();

Check Connection Status #

String status = await printer.getPrinterStatus();
print('Printer status: $status'); // 'connected', 'disconnected', 'connecting'

Print Operations #

Print Text

await printer.printText(
  'Hello World!',
  width: 48,  // Label width in mm
  height: 50, // Label height in mm
);

Print 1D Barcode

await printer.print1DBarcode(
  '1234567890',           // Barcode data
  text: 'Product Label',  // Optional text above barcode
  width: 48,
  height: 50,
);

Print QR Code

await printer.print2DBarcode(
  'https://example.com', // QR code data
  width: 48,
  height: 50,
);

Print Image

// Convert image to base64
String base64Image = base64Encode(imageBytes);
await printer.printImage(base64Image);

Adjust Print Settings #

Set Print Density (Darkness)

await printer.setPrintDensity(10); // 0 (lightest) to 20 (darkest)

Set Print Speed

await printer.setPrintSpeed(3); // 1 (slowest) to 5 (fastest)

Disconnect #

await printer.disconnectPrinter();

Complete Example #

import 'package:flutter/material.dart';
import 'package:flutter_dothantech_lpapi_thermal_printer/flutter_dothantech_lpapi_thermal_printer.dart';
import 'package:permission_handler/permission_handler.dart';

class PrinterExample extends StatefulWidget {
  @override
  _PrinterExampleState createState() => _PrinterExampleState();
}

class _PrinterExampleState extends State<PrinterExample> {
  final printer = LpapiThermalPrinter();
  List<PrinterInfo> printers = [];
  String status = 'Disconnected';

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

  Future<void> checkStatus() async {
    String s = await printer.getPrinterStatus();
    setState(() {
      status = s;
    });
  }

  Future<void> discoverPrinters() async {
    // Request permissions first
    await [
      Permission.bluetooth,
      Permission.bluetoothScan,
      Permission.bluetoothConnect,
      Permission.location,
    ].request();

    // Discover printers
    List<PrinterInfo> found = await printer.discoverPrinters();
    setState(() {
      printers = found;
    });
  }

  Future<void> connectAndPrint(String address) async {
    // Connect
    bool connected = await printer.connectPrinter(address);
    if (!connected) {
      print('Failed to connect');
      return;
    }

    // Set print settings
    await printer.setPrintDensity(8);
    await printer.setPrintSpeed(3);

    // Print text
    await printer.printText('Hello from Flutter!');

    // Print barcode
    await printer.print1DBarcode(
      '1234567890',
      text: 'Product SKU',
    );

    // Print QR code
    await printer.print2DBarcode('https://example.com');

    // Disconnect
    await printer.disconnectPrinter();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Printer Example')),
      body: Column(
        children: [
          Text('Status: $status'),
          ElevatedButton(
            onPressed: discoverPrinters,
            child: Text('Discover Printers'),
          ),
          Expanded(
            child: ListView.builder(
              itemCount: printers.length,
              itemBuilder: (context, index) {
                final p = printers[index];
                return ListTile(
                  title: Text(p.name),
                  subtitle: Text(p.address),
                  onTap: () => connectAndPrint(p.address),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}

API Reference #

PrinterInfo Class #

class PrinterInfo {
  final String name;    // Printer name
  final String address; // MAC address
  final String type;    // 'PAIRED' or 'DISCOVERED'
}

LpapiThermalPrinter Methods #

Troubleshooting #

Note: This plugin has been thoroughly tested with the P1 Series Label Printer. If you're using a different Dothantech printer model, the functionality should be similar, but some features may vary.

Printer not found during discovery #

1. Ensure Bluetooth is enabled on your device
2. Check that all required permissions are granted
3. Make sure the printer is powered on and in range
4. Try both searchPrinters() (for paired) and discoverPrinters() (for all)

Connection fails #

1. Verify the printer MAC address is correct
2. Ensure no other device is connected to the printer
3. Try disconnecting and reconnecting
4. Power cycle the printer if necessary

Print quality issues #

• Adjust print density: Higher values (15-20) for darker prints
• Adjust print speed: Lower values (1-2) for better quality
• Ensure the label size parameters match your actual labels

Android 12+ Permission Issues #

For Android 12 and above, location permission is required for Bluetooth scanning. Make sure to:

1. Request permissions at runtime
2. Enable location services on the device
3. Add all required permissions to AndroidManifest.xml

iOS Bluetooth Issues #

For iOS devices:

1. Ensure Bluetooth permissions are added to Info.plist
2. Make sure the device's Bluetooth is turned on
3. The printer must be in pairing/discoverable mode
4. iOS may cache Bluetooth connections - try restarting the app if connection fails

Contributing #

Contributions are welcome! Please feel free to submit a Pull Request.

Development Setup #

1. Clone the repository
2. Run flutter pub get in both root and example directories
3. Connect an Android device or emulator
4. Run the example app: cd example && flutter run

License #

This project is licensed under the MIT License - see the LICENSE file for details.

Credits #

This plugin uses the Dothantech LPAPI SDK for printer communication.

Support #

For issues, questions, or contributions, please visit the GitHub repository.