flutter 蓝牙打印

Flutter提供了一个flutter_bluetooth_serial库，可以用于在移动设备上与蓝牙设备进行通信。下面是一个示例代码，演示如何使用flutter_bluetooth_serial库来连接并打印到蓝牙打印机。

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

class BluetoothPrintExample extends StatefulWidget {
  @override
  _BluetoothPrintExampleState createState() => _BluetoothPrintExampleState();
}

class _BluetoothPrintExampleState extends State<BluetoothPrintExample> {
  BluetoothConnection connection;
  bool _connected = false;
  List<int> bytes = utf8.encode("Hello world!\n\n\n");

  void _connect() async {
    BluetoothDevice selectedDevice = await Navigator.of(context).push(
      MaterialPageRoute(
        builder: (context) => BluetoothDeviceList(),
      ),
    );

    if (selectedDevice != null) {
      await BluetoothConnection.toAddress(selectedDevice.address)
          .then((_connection) {
        print('Connected to the device');
        connection = _connection;
        setState(() {
          _connected = true;
        });
      }).catchError((error) {
        print('Cannot connect, exception occurred');
        print(error);
      });
    } else {
      print('No device selected');
    }
  }

  void _disconnect() {
    connection.close();
    setState(() {
      _connected = false;
    });
  }

  void _print() {
    connection.output.add(bytes);
    setState(() {
      _connected = true;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Bluetooth Print Example'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            RaisedButton(
              onPressed: _connect,
              child: Text('Connect'),
            ),
            RaisedButton(
              onPressed: _disconnect,
              child: Text('Disconnect'),
            ),
            RaisedButton(
              onPressed: _print,
              child: Text('Print'),
            ),
          ],
        ),
      ),
    );
  }
}

class BluetoothDeviceList extends StatefulWidget {
  @override
  _BluetoothDeviceListState createState() => _BluetoothDeviceListState();
}

class _BluetoothDeviceListState extends State<BluetoothDeviceList> {
  List<BluetoothDevice> _devicesList = [];
  BluetoothDevice _device;

  @override
  void initState() {
    super.initState();
    FlutterBluetoothSerial.instance
        .getBondedDevices()
        .then((List<BluetoothDevice> devices) {
      setState(() {
        _devicesList = devices;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Select Device'),
      ),
      body: ListView.builder(
        itemCount: _devicesList.length,
        itemBuilder: (BuildContext context, int index) {
          return ListTile(
            title: Text(_devicesList[index].name),
            subtitle: Text(_devicesList[index].address),
            onTap: () {
              _device = _devicesList[index];
              Navigator.pop(context, _device);
            },
          );
        },
      ),
    );
  }
}

这个示例代码提供了三个按钮：Connect、Disconnect、Print。在点击Connect按钮后，会打开一个页面，显示所有已配对的蓝牙设备。用户可以选择要连接的设备。在连接成功后，点击Print按钮可以将“Hello world！”打印到蓝牙打印机。

请注意，此示例假定您已经了解了flutter_bluetooth_serial库的基本用法，因此省略了一些错误处理和异常处理。