用 flutter 使用flutter_blue写一个domo

好的，下面是简单的 Flutter Blue demo：

首先需要在 `pubspec.yaml` 中添加依赖：

dependencies:
  flutter_blue: ^0.7.3

然后在代码中导入 `flutter_blue`：

import 'package:flutter_blue/flutter_blue.dart';

接下来，我们可以创建一个 `BluetoothManager` 类来管理蓝牙扫描和连接：

class BluetoothManager {
  FlutterBlue flutterBlue = FlutterBlue.instance;
  StreamSubscription<ScanResult> _scanSubscription;
  BluetoothDevice _connectedDevice;

  Future<bool> scanForDevices() async {
    try {
      _scanSubscription = flutterBlue.scan().listen((scanResult) {
        print('Found device: ${scanResult.device.name}');
      });
      return true;
    } catch (e) {
      print(e.toString());
      return false;
    }
  }

  Future<bool> connectToDevice(String deviceId) async {
    try {
      var device = await flutterBlue.connect(deviceId);
      _connectedDevice = device;
      return true;
    } catch (e) {
      print(e.toString());
      return false;
    }
  }

  void disconnectFromDevice() {
    if (_connectedDevice != null) {
      _connectedDevice.disconnect();
      _connectedDevice = null;
    }
  }

  void stopScan() {
    _scanSubscription?.cancel();
    _scanSubscription = null;
  }
}

此时，我们就可以在 UI 中使用上述方法了。例如，我们可以创建一个 `ScanButton`，当用户点击按钮时开始扫描：

class ScanButton extends StatefulWidget {
  @override
  _ScanButtonState createState() => _ScanButtonState();
}

class _ScanButtonState extends State<ScanButton> {
  bool isScanning = false;

  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      child: Text(isScanning ? 'Stop scan' : 'Start scan'),
      onPressed: () async {
        if (isScanning) {
          BluetoothManager().stopScan();
        } else {
          BluetoothManager().scanForDevices();
        }

        setState(() {
          isScanning = !isScanning;
        });
      },
    );
  }
}

我们也可以创建一个 `ConnectButton`，当用户点击按钮时连接到设备：

class ConnectButton extends StatefulWidget {
  final String deviceId;

  ConnectButton({this.deviceId});

  @override
  _ConnectButtonState createState() => _ConnectButtonState();
}

class _ConnectButtonState extends State<ConnectButton> {
  bool isConnected = false;

  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      child: Text(isConnected ? 'Disconnect' : 'Connect'),
      onPressed: () async {
        if (isConnected) {
          BluetoothManager().disconnectFromDevice();
        } else {
          BluetoothManager().connectToDevice(widget.deviceId);
        }

        setState(() {
          isConnected = !isConnected;
        });
      },
    );
  }
}

最后，我们可以在 UI 中使用这两个按钮：

class BluetoothDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Bluetooth Demo')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            ScanButton(),
            SizedBox(height: 16),
            ConnectButton(deviceId: 'device-id-here'),
          ],
        ),
      ),
    );
  }
}

请注意，这只是一个简单的 demo，并没有处理错误处理和连接状态更新等问题。