我收到血压测量的原始数据：[DE, E2, F4, 3E, F3, FF, 07, E8, 07, 03, 13, 02, 21, 00, 34, F3, 01, C0, 00]。我设法读取了收缩压、舒张压以及脉搏的值。然而，当我尝试读取平均动脉压 (meanAP) 的值（通常应在索引 5 和 6 处占用两个字节 (FF,07)）时，我收到了meanAP=-20.41 mmHg。而使用 nRF Connect 时，它等于 2047.0 mmHg。请问我该如何在下面的代码中纠正这个问题？
import 'package:flutter/material.dart';
import 'package:flutter_reactive_ble/flutter_reactive_ble.dart';
import 'dart:typed_data';
import 'dart:math';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'BLE Scanner',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final FlutterReactiveBle flutterReactiveBle = FlutterReactiveBle();
List<DiscoveredDevice> devices = [];
double systolic = 0;
double diastolic = 0;
List<double> result = [
0.0,
0.0,
0.0,
0.0,
]; // Déclaration de la variable result
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Mesurer votre Pression Arterielle'),
backgroundColor: Colors.blue,
),
body: Padding(
padding: EdgeInsets.all(20.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
ElevatedButton(
onPressed: _scanForDevices,
child: Text('Rechercher votre appareil BM96'),
style: ElevatedButton.styleFrom(
foregroundColor: Colors.white,
backgroundColor: Colors.blue,
),
),
SizedBox(height: 20),
Text(
'Discovered Devices:',
style: TextStyle(
fontSize: 18,
fontWeight: FontWeight.bold,
color: Colors.blue,
),
),
SizedBox(height: 10),
Expanded(
child: ListView.builder(
itemCount: devices.length,
itemBuilder: (context, index) {
final device = devices[index];
return ListTile(
title: Text(
device.name ?? 'Unknown',
style: TextStyle(
fontSize: 16,
color: Colors.black,
),
),
subtitle: Text(
device.id,
style: TextStyle(
fontSize: 14,
color: Colors.grey,
),
),
onTap: () {
_connectToDevice(device.id);
_subscribeToBloodPressureMeasurement(device.id);
},
);
},
),
),
SizedBox(height: 20),
Text(
'Result Systolic: ${result[0]}',
style: TextStyle(fontSize: 20),
),
SizedBox(height: 10),
Text(
'Result Diastolic: ${result[1]}',
style: TextStyle(fontSize: 20),
),
SizedBox(height: 10),
Text(
'Result pulse: ${result[2]}',
style: TextStyle(fontSize: 20),
),
SizedBox(height: 10),
Text(
'Result MeanAP: ${result[3]}',
style: TextStyle(fontSize: 20),
),
],
),
),
);
}
void _scanForDevices() {
flutterReactiveBle.scanForDevices(
withServices: [Uuid.parse('00001810-0000-1000-8000-00805f9b34fb')],
scanMode: ScanMode.lowLatency,
).listen(
(device) {
final existingDeviceIndex =
devices.indexWhere((d) => d.id == device.id);
if (existingDeviceIndex != -1) {
setState(() {
devices[existingDeviceIndex] = device;
});
} else {
setState(() {
devices.add(device);
});
}
},
onError: (error) {
print('Error: $error');
},
);
}
void _connectToDevice(String deviceId) {
flutterReactiveBle
.connectToDevice(
id: deviceId,
servicesWithCharacteristicsToDiscover: {
Uuid.parse('00001810-0000-1000-8000-00805f9b34fb'): [
Uuid.parse('00002a35-0000-1000-8000-00805f9b34fb'),
Uuid.parse('00002a49-0000-1000-8000-00805f9b34fb'),
],
},
connectionTimeout: const Duration(seconds: 2),
)
.listen(
(connectionState) {
if (connectionState == DeviceConnectionState.connected) {
print("Connected successfully to device: $deviceId");
_subscribeToBloodPressureMeasurement(deviceId);
}
},
onError: (error) {
print('Error connecting to device: $error');
},
);
}
void _subscribeToBloodPressureMeasurement(String deviceId) {
try {
final bloodPressureCharacteristic = QualifiedCharacteristic(
characteristicId: Uuid.parse('00002a35-0000-1000-8000-00805f9b34fb'),
deviceId: deviceId,
serviceId: Uuid.parse('00001810-0000-1000-8000-00805f9b34fb'),
);
flutterReactiveBle
.subscribeToCharacteristic(bloodPressureCharacteristic)
.listen(
(data) {
print('Received raw data for blood pressure measurement: $data');
setState(() {
result = parseBloodPressureData(data);
});
},
onError: (error) {
print('Error subscribing to blood pressure measurement: $error');
},
);
} catch (e) {
print('Exception during subscribing to blood pressure measurement: $e');
}
}
List<double> parseBloodPressureData(List<int> packet) {
final data = ByteData.sublistView(Uint8List.fromList(packet));
const startByte = 1;
int value = 0;
//systolic
value = data.getInt16(startByte, Endian.little);
int mantissa = value & 0xfff;
if (mantissa >= 0x0800) {
mantissa = -((0x0FFF + 1) - mantissa);
}
int exponent = value >> 12;
if (exponent >= 0x0008) {
exponent = -((0x000F + 1) - exponent);
}
double magnitude = pow(10.0, exponent).toDouble();
double systolic = mantissa * magnitude;
//diastolic
value = data.getInt16(startByte + 2, Endian.little);
mantissa = value & 0xfff;
if (mantissa >= 0x0800) {
mantissa = -((0x0FFF + 1) - mantissa);
}
exponent = value >> 12;
if (exponent >= 0x0008) {
exponent = -((0x000F + 1) - exponent);
}
magnitude = pow(10.0, exponent).toDouble();
double diastolic = mantissa * magnitude;
//pulse
value = data.getInt16(startByte + 13, Endian.little);
mantissa = value & 0xfff;
if (mantissa >= 0x0800) {
mantissa = -((0x0FFF + 1) - mantissa);
}
exponent = value >> 12;
if (exponent >= 0x0008) {
exponent = -((0x000F + 1) - exponent);
}
magnitude = pow(10.0, exponent).toDouble();
double pulse = mantissa * magnitude;
//meanAP
value = data.getInt16(startByte + 5, Endian.little);
mantissa = value & 0xfff;
if (mantissa >= 0x0800) {
mantissa = -((0x0FFF + 1) - mantissa);
}
exponent = value >> 12;
if (exponent >= 0x0008) {
exponent = -((0x000F + 1) - exponent);
}
magnitude = pow(10.0, exponent).toDouble();
double meanAP= mantissa * magnitude;
return [systolic, diastolic, pulse,meanAP];
}
}
处理占用多个字节的 BLE 数据时，很容易忽略的一件事是 Endianness。字节的放置顺序至关重要。以你的价值观为例：
0xFF07 = 65287
0x07FF = 2047
有趣的是，您已经使用 Little Endian 提取了 int16 值。我在 DartPad 上尝试了你的代码并收到了 2047 结果：
import 'dart:typed_data';
import 'dart:math';
void main() {
final data = ByteData.sublistView(Uint8List.fromList([0xFF, 0x07]));
int value = data.getInt16(0, Endian.little);
int mantissa = value & 0xfff;
if (mantissa >= 0x0800) {
mantissa = -((0x0FFF + 1) - mantissa);
}
int exponent = value >> 12;
if (exponent >= 0x0008) {
exponent = -((0x000F + 1) - exponent);
}
double magnitude = pow(10.0, exponent).toDouble();
double meanAP= mantissa * magnitude;
print(meanAP);
}