How to use flutter_blue in general

bleCore.dart

import 'dart:async';
/* If there is an error that points about the minSdkVersion, 
change the number (minSdkVersion 16) to 19 in $PROJECT_ROOT/android/app/build.gradle */
// example: https://github.com/pauldemarco/flutter_blue/tree/master/example/lib
import 'package:flutter_blue/flutter_blue.dart'; // for BLE
import 'package:flutter/material.dart';
import 'utils/enums.dart';

class BLEData {
  // "00010000-0002-1000-8000-00805f9b34fb"
  List<BluetoothDevice> devicesScanned;
  List<BluetoothService> servicesFound;
  BluetoothDevice targetDevice;
  BluetoothCharacteristic targetChar;

  BLEData() {
    devicesScanned = List<BluetoothDevice>();
    servicesFound = List<BluetoothService>();
    targetDevice = null;
    targetChar = null;
  }
}

class BLECore {
  // Main instance and flag
  FlutterBlue _flutterBlue;
  bool _flutterBlueState;
  BLEActivityStatus _bleActivityState;
  bool _debugMode;
  // Scanned/discoverred items
  BLEData _bleData;

  // handlers
  StreamSubscription<BluetoothState> _stateSubscription;
  Function _doneHandler;
  Function _dataHandler;

  BLECore(
      bool debugMode, Function givenDoneHandler, Function givenDataHandler) {
    _bleData = BLEData();

    _flutterBlue = FlutterBlue.instance;
    _flutterBlueState = false;
    _bleActivityState = BLEActivityStatus.init;
    _debugMode = debugMode;

    _doneHandler = givenDoneHandler;
    _dataHandler = givenDataHandler;
    _stateSubscription =
        _flutterBlue.state.listen((data) => this.stateHandler(data));
  }

  getFlutterBlueState() => _flutterBlueState;
  cancelStateSubscription() => _stateSubscription.cancel();
  void stateHandler(BluetoothState state) {
    switch (state) {
      case BluetoothState.on:
        if (_bleActivityState == BLEActivityStatus.notAvailable) {
          _bleActivityState = BLEActivityStatus.init;
        }
        _flutterBlueState = true;
        break;
      case BluetoothState.off:
      case BluetoothState.turningOff:
      case BluetoothState.turningOn:
      case BluetoothState.unauthorized:
      case BluetoothState.unavailable:
      case BluetoothState.unknown:
      default:
        _bleActivityState = BLEActivityStatus.notAvailable;
        _flutterBlueState = false;
        break;
    }
  }

  bool checkBleActivityState() {
    if (_debugMode) {
      debugPrint("[BLE Core] >> " + _bleActivityState.toString());
    }

    if (_bleActivityState != BLEActivityStatus.init ||
        _bleActivityState == BLEActivityStatus.notAvailable) {
      return false;
    }
    return true;
  }

  void scan() async {
    if (!checkBleActivityState()) {
      // Don't allow multiple BLE activities at a moment
      return;
    }
    // Set and reset the variables
    _bleActivityState = BLEActivityStatus.scanning;
    _bleData.devicesScanned.clear();

    // Scan!
    var scanResult;
    try {
      scanResult = await _flutterBlue.startScan(timeout: Duration(seconds: 4));
    } catch (e) {
      debugPrint(e.toString());
      _bleActivityState = BLEActivityStatus.init;
      return;
    }

    for (var r in scanResult) {
      var device = r.device;
      var deviceName = r.device.name.toString();

      // Filter the anonymous devices out
      if (deviceName.length > 0) {
        _bleData.devicesScanned.add(device);

        if (_debugMode) {
          debugPrint("[BLE Core] >> " + deviceName);
        }
      }
    }

    _bleActivityState = BLEActivityStatus.init;
    _doneHandler(Request.scan);
  }

  List<BluetoothDevice> getBleDevicesScanned() {
    if (!checkBleActivityState()) {
      // Don't allow multiple BLE activities at a moment
      return [];
    }

    if (_bleData.devicesScanned.length == 0) {
      return [];
    }

    if (_bleActivityState == BLEActivityStatus.scanning) {
      return [];
    }

    // Leave this here for debugging later.
    // if (_debugMode && _bleData.devicesScanned.length > 0) {
    //   _bleData.devicesScanned.forEach(
    //     (device) => {
    //       debugPrint(
    //         "[BLE Core] >> " +
    //             device.id.toString() +
    //             " / " +
    //             device.name.toString() +
    //             " / " +
    //             device.type.toString(),
    //       ),
    //     },
    //   );
    // }

    return _bleData.devicesScanned;
  }

  void connect(String device) async {
    if (!checkBleActivityState()) {
      // Don't allow multiple BLE activities at a moment
      return;
    }
    _bleActivityState = BLEActivityStatus.connecting;

    // Find and disconnect if there is any connected BLE device
    List<BluetoothDevice> connectedDevices =
        await _flutterBlue.connectedDevices;
    for (var c in connectedDevices) {
      await c.disconnect();
    }

    // Find and connect if there is a matched device in the list
    for (var d in _bleData.devicesScanned) {
      if (device.contains(d.id.toString())) {
        _bleData.targetDevice = d;
        break;
      }
    }
    try {
      await _bleData.targetDevice.connect(timeout: Duration(seconds: 10));
      await _bleData.targetDevice.requestMtu(192);
    } catch (e) {
      debugPrint(e.toString());
      _bleActivityState = BLEActivityStatus.init;
      _doneHandler(Request.failed);
      return;
    }

    _bleActivityState = BLEActivityStatus.init;
    _doneHandler(Request.connect);
  }

  void discoverServices() async {
    if (!checkBleActivityState()) {
      // Don't allow multiple BLE activities at a moment
      return;
    }
    _bleActivityState = BLEActivityStatus.discoverring;

    // Discover services if there is a connected device
    _bleData.servicesFound.clear();
    if (_bleData.targetDevice != null) {
      try {
        _bleData.servicesFound = await _bleData.targetDevice
            .discoverServices()
            .timeout(const Duration(seconds: 1));
      } catch (e) {
        debugPrint(e.toString());
      }
    }

    _bleActivityState = BLEActivityStatus.init;
    // Service discovery fails a lot.
    // To get back to the state of CONNECTED,
    // the length of the found service list should be checked.
    // Also, don't report it is failed.
    if (_bleData.servicesFound.length == 0) {
      _doneHandler(Request.connect);
    } else {
      _doneHandler(Request.discoverServices);
    }
  }

  void readTargetCharacteristic(String targetUuid) async {
    if (!checkBleActivityState()) {
      // Don't allow multiple BLE activities at a moment
      return;
    }
    _bleActivityState = BLEActivityStatus.reading;

    _bleData.targetChar = null;
    for (int i = 0; i < _bleData.servicesFound.length; i++) {
      for (BluetoothCharacteristic c
          in _bleData.servicesFound[i].characteristics) {
        try {
          await Future.delayed(Duration(milliseconds: 10));
          if (c.properties.read && c.uuid.toString().contains(targetUuid)) {
            _bleData.targetChar = c;
          }
        } catch (e) {
          debugPrint("Error!: " + e.toString());
          _bleActivityState = BLEActivityStatus.init;
          _doneHandler(Request.failed);
          return;
        }
      }
    }

    _bleActivityState = BLEActivityStatus.init;
    _doneHandler(Request.readCharacteristics);
  }

  void readTargetValue(String targetUuid) async {
    if (!checkBleActivityState()) {
      // Don't allow multiple BLE activities at a moment
      return;
    }
    _bleActivityState = BLEActivityStatus.reading;

    try {
      String tmp = "";
      var val =
          await _bleData.targetChar.read().timeout(const Duration(seconds: 1));

      // Int to ascii string
      val.forEach((v) => {tmp += String.fromCharCode(v)});

      debugPrint(tmp.toString());
      _dataHandler(Request.readValues, tmp.toString());
    } catch (e) {
      debugPrint(e.toString());
      _bleActivityState = BLEActivityStatus.init;
      _doneHandler(Request.failed);
      return;
    }

    _bleActivityState = BLEActivityStatus.init;
    _doneHandler(Request.readValues);
  }

  void writeTargetValue(List<int> data) async {
    debugPrint(data.toString());
    // Check the type and length of the incoming param
    if (data == null) {
      return;
    } else if (data.length != 192) {
      return;
    }

    if (!checkBleActivityState()) {
      // Don't allow multiple BLE activities at a moment
      return;
    }
    _bleActivityState = BLEActivityStatus.writing;

    int mtu = await _bleData.targetDevice.mtu.first;
    if (mtu == 192) {
      // Never put NULL value to the write API
      for (int i = 0; i < data.length; i++) {
        if (data[i] == null) {
          data[i] = 0;
        }
      }

      try {
        await _bleData.targetChar
            .write(data)
            .timeout(const Duration(seconds: 1));
      } catch (e) {
        debugPrint(e.toString());
        _bleActivityState = BLEActivityStatus.init;
        _doneHandler(Request.failed);
        return;
      }
    }

    _bleActivityState = BLEActivityStatus.init;
    _doneHandler(Request.writeValues);
  }

  void setNotifier() {
    if (_bleData.targetChar != null) {
      try {
        _bleData.targetChar.setNotifyValue(true);
        _bleData.targetChar.value.listen(
          (data) => {
            debugPrint(""),
          },
        );
      } catch (e) {
        debugPrint(e.toString());
      }
    }
  }

  void disconnect() async {
    if (_bleActivityState == BLEActivityStatus.notAvailable) {
      return;
    }
    _bleActivityState = BLEActivityStatus.disconnecting;

    try {
      _bleData.targetDevice.disconnect();

      List<BluetoothDevice> connectedDevices =
          await _flutterBlue.connectedDevices;
      for (var c in connectedDevices) {
        c.disconnect();
      }
    } catch (e) {
      debugPrint(e.toString());
      _bleActivityState = BLEActivityStatus.init;
      _doneHandler(Request.failed);
      return;
    }

    _bleActivityState = BLEActivityStatus.init;
    _doneHandler(Request.disconnect);
  }
}

This is a simple and dirty example to use the flutter_blue plugin.
There is a upper layer as a provider's model. This and that code utilize some enums to deal with the work.

That would be great if u can show BLEActivityStatus file for us to see.

That would be great if u can show BLEActivityStatus file for us to see.

// This can be used for the BLECore
enum BLEActivityStatus {
  notAvailable,
  init,
  scanning,
  connecting,
  disconnecting,
  discovering,
  reading,
  writing,
}

It is just an enum that can be used as a flag to prevent calling a same API (i.e. calling the scan API while a previous scan is being used).

That would be great if u can show BLEActivityStatus file for us to see.

// This can be used for the BLECore
enum BLEActivityStatus {
  notAvailable,
  init,
  scanning,
  connecting,
  disconnecting,
  discovering,
  reading,
  writing,
}

It is just an enum that can be used as a flag to prevent calling a same API (i.e. calling the scan API while a previous scan is being used).

thanks