从字节中获取字符串（Corebluetooth，Swift）

Question

只是为了看看是否有人可以帮助我解决一些 BLE 问题。我正在尝试制作一个从划船机中获取内容的应用程序，但我不知道如何将字节转换为字符串？很难解释，但这是我的 VC：

import UIKit
import CoreBluetooth


let rowerServiceCBUUID = CBUUID(string: "CE060000-43E5-11E4-916C-0800200C9A66")
let characteristic1CBUUID = CBUUID(string: "CE060031-43E5-11E4-916C-0800200C9A66")
let characteristic2CBUUID = CBUUID(string: "2AD1")
class HRMViewController: UIViewController {
  @IBOutlet weak var heartRateLabel: UILabel!
  @IBOutlet weak var bodySensorLocationLabel: UILabel!
  var centralManager: CBCentralManager!
  var pmPeripheral: CBPeripheral!
  var wattValue: Int!
  override func viewDidLoad() {
    super.viewDidLoad()
    centralManager = CBCentralManager(delegate: self, queue: nil)
    // Make the digits monospaces to avoid shifting when the numbers change
    heartRateLabel.font = UIFont.monospacedDigitSystemFont(ofSize: heartRateLabel.font!.pointSize, weight: .regular)
  }

  func onHeartRateReceived(_ heartRate: Int) {
    heartRateLabel.text = String(heartRate)
    print("BPM: \(heartRate)")
  }
}
extension HRMViewController: CBCentralManagerDelegate {
  func centralManagerDidUpdateState(_ central: CBCentralManager) {
      print("Central state update")
      if central.state != .poweredOn {
          print("Central is not powered on")
      } else {
          print("Central scanning for", rowerServiceCBUUID);
          centralManager.scanForPeripherals(withServices: [rowerServiceCBUUID],
                                            options: [CBCentralManagerScanOptionAllowDuplicatesKey : true])
      }
  }

  func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
    print(peripheral)
    peripheral.delegate = self
    pmPeripheral = peripheral
    pmPeripheral.delegate = self
    centralManager.stopScan()
    centralManager.connect(pmPeripheral!)
  }
  func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    print("Connected!")
    pmPeripheral.discoverServices(nil)
  }

}
extension HRMViewController: CBPeripheralDelegate {
  func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
    guard let services = peripheral.services else { return }
    for service in services {
      print(service)
      print(service.characteristics ?? "characteristics are nil")
      peripheral.discoverCharacteristics(nil, for: service)
    }
  }
  func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?){
    guard let characteristics = service.characteristics else { return }
    for characteristic in characteristics {
      print(characteristic)
      if characteristic.properties.contains(.read) {
        print("\(characteristic.uuid): properties contains .read")
      }
      if characteristic.properties.contains(.notify) {
        print("\(characteristic.uuid): properties contains .notify")
      }
      peripheral.readValue(for: characteristic)
    }
  }
  func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic,
                  error: Error?) {
    switch characteristic.uuid {
      case characteristic1CBUUID:
        let bodySensorLocation = bodyLocation(from: characteristic)
        bodySensorLocationLabel.text = bodySensorLocation
      default:
        print("Unhandled Characteristic UUID: \(characteristic.uuid)")
    }
  }
  private func bodyLocation(from characteristic: CBCharacteristic) -> String {
    guard let characteristicData = characteristic.value,
      let byte = characteristicData.first else { return "Error" }
    switch byte {
      case 0: return "0"
      case 1: return "1"
      case 2: return "2"
      case 3: return "3"
      case 4: return "4"
      case 5: return "5"
      case 6: return "6"
      case 7: return "7"
      case 8: return "8"
      default:
        return "Reserved for future use"
    }
  }
}

特别是最底部的文本是我卡住的地方，每个 Corebluetooth 指南都将数字交换为文本，但我的是一个字符串数组（如下所示：https://youtu.be/rXDCBVQXdbg）

我被困住了，不知道从这里去哪里。对此的任何帮助将不胜感激！

Answer 1

从您使用的 UUID 来看，您目前关注的是Concept2 Performance Monitor Bluetooth Smart Communications Interface Definition 第 11 页上记录的C2 划船一般状态特征。

文档说该消息将由 19 个字节组成：

• 字节 0：经过时间 Lo（0.01 秒 lsb）
• 字节 1：中间经过的时间
• 字节 2：经过时间高
• 字节 3：距离 Lo (0.1 m lsb)
• 字节 4：中距离
• 字节 5：距离高
• 字节 6：锻炼类型（枚举）
• ...

经过的时间存储在 3 个字节中：字节 0 是最低有效字节 (LSB)，然后是中字节和高字节。单位为0.01s。所以要获得秒数，必须除以 100。

距离的存储方式类似。单位是0.1m。

锻炼类型在字节 6 中作为枚举给出。所以不包含文本。只是一个数字代码。

要对其进行解码，请使用如下代码。函数onRowingGeneralStatusUpdate(for:) 替换了你容易混淆的函数bodyLocation(from:)：

func onRowingGeneralStatusUpdate(characteristic: CBCharacteristic) {
    guard let data = characteristic.value else { return }

    // elapsed time in sec
    let elapsedTime: Double = Double(Int(data[0]) + 256 * Int(data[1]) + 65536 * Int(data[2])) / 100.0
    // distance in m
    let distance: Double = Double(Int(data[3]) + 256 * Int(data[4]) + 65536 * Int(data[5])) / 10.0
    let workout: String =  workoutType(for: data[6])
}

func workoutType(for code: UInt8) -> String {
    switch code {
    case 0:
        return "Just row, no splits"
    case 1:
        return "Just row, splits"
    case 2:
        return "Fixed dist, no splits"
    case 3:
        return "Fixed dist, splits"
    case 4:
        return "Fixed time, no splits"
    case 5:
        return "Fixed time, splits"
    case 6:
        return "Fixed time, interval"
    case 7:
        return "Fixed dist, interval"
    case 8:
        return "Variable, interval"
    case 9:
        return "Variable, undef rest, interval"
    case 10:
        return "Fixed, calorie"
    case 11:
        return "Fixed, watt-minutes"
    case 12:
        return "Fixed cals, interval"
    default:
        return ""
    }
}