藍(lán)牙屬于近場(chǎng)通訊中的一種宛畦，iOS 中使用Core Bluetooth 框架實(shí)現(xiàn)藍(lán)牙通信， Core Bluetooth支持藍(lán)牙低功耗的4.0模式，就是通常說(shuō)稱(chēng)之的BLE渗常，在生活中BLE無(wú)處不在掠械，例如智能家居由缆，健身器材和智能玩具等，利用蘋(píng)果提供的Core Bluetooth框架可以實(shí)現(xiàn)和BLE設(shè)備進(jìn)行通信猾蒂。

藍(lán)牙中各角色的理解

在藍(lán)牙開(kāi)發(fā)中我們把提供服務(wù)的一方稱(chēng)之為周邊設(shè)備均唉，接收服務(wù)的一方稱(chēng)之為中央設(shè)備，典型的例子就是蘋(píng)果手表和iPhone配對(duì)時(shí)的關(guān)系肚菠，蘋(píng)果手表向iPhone提供用戶(hù)的運(yùn)動(dòng)數(shù)據(jù)舔箭，所以此種情況蘋(píng)果手表是周邊設(shè)備，iPhone是中央設(shè)備，在Core Bluetooth 框架中分別對(duì)應(yīng)如下：

• centralManager：中央設(shè)備的處理類(lèi)
• peripheralManager：周邊設(shè)備的處理類(lèi)

明確了周邊設(shè)備和中央設(shè)備后层扶，接下來(lái)是如何發(fā)現(xiàn)對(duì)方并建立連接箫章，在我們平時(shí)使用的手機(jī)搜索藍(lán)牙的過(guò)程中，都是先從搜索列表中選擇某個(gè)藍(lán)牙設(shè)備镜会，在進(jìn)行配對(duì)連接檬寂。peripheral通過(guò)廣播的形式向外界提供service，service會(huì)綁定一個(gè)獨(dú)一無(wú)二的UUID戳表，有BTSIG UUID和Custom UUID二種桶至，UUID用來(lái)確定中央設(shè)備連接周邊設(shè)備時(shí)確定身份用的。

每個(gè)service會(huì)有多個(gè)characteristic匾旭，characteristic也有自己的UUID镣屹，characteristic可以理解為周邊設(shè)備提供的具體服務(wù)，其UUID用來(lái)區(qū)分提供的每一個(gè)具體服務(wù)价涝，因?yàn)橐粋€(gè)service是可以提供多種具體服務(wù)的女蜈，中央設(shè)備通過(guò)UUID來(lái)讀寫(xiě)這些服務(wù)。

在雙方建立了連接后就要商議如何發(fā)送和接受數(shù)據(jù)了飒泻，數(shù)據(jù)傳輸協(xié)議部分我們不用細(xì)究鞭光，Core Bluetooth都為我們處理好了，至于MTU最大最大傳輸單元現(xiàn)在是是271bytes泞遗，數(shù)據(jù)超過(guò)了就會(huì)分段發(fā)送惰许。

實(shí)戰(zhàn)演示

CBPeripheralManager

新建一個(gè)PeripheralViewController類(lèi)并繼承UIViewController，定義成員變量peripheralManager并初始化史辙，同時(shí)設(shè)置代理汹买，由于篇幅有限這里只貼出關(guān)鍵代碼：

peripheralManager = CBPeripheralManager(delegate: self, queue: nil)

Peripheral Manager delegate

代理必須實(shí)現(xiàn)的方法如下：

extension PeripheralViewController: CBPeripheralManagerDelegate {
  func peripheralManagerDidUpdateState(_ peripheral: CBPeripheralManager) {
    switch peripheral.state {
    case .poweredOn:
      textCharacteristic = CBMutableCharacteristic(type: textCharacteristicUUID, properties: .notify, value: nil, permissions: .readable)
      mapCharacteristic = CBMutableCharacteristic(type: mapCharacteristicUUID, properties: .writeWithoutResponse, value: nil, permissions: .writeable)
      let service = CBMutableService(type: TextOrMapServiceUUID, primary: true)
      service.characteristics = [textCharacteristic, mapCharacteristic]
      peripheralManager.add(service)
    default: return
    }
  }

當(dāng)藍(lán)牙服務(wù)可用時(shí)，需要?jiǎng)?chuàng)建service并關(guān)聯(lián)相應(yīng)的characteristic聊倔，代碼中的UUID都是定義的字符串常量晦毙。

peripheralManager.startAdvertising([CBAdvertisementDataServiceUUIDsKey: [TextOrMapServiceUUID]])

通過(guò)startAdvertising方法來(lái)向外界發(fā)送廣播。

由于iOS的限制耙蔑，當(dāng)iOS設(shè)備作為周邊設(shè)備向外廣播時(shí)是無(wú)法利用CBAdvertisementDataManufacturerDataKey攜帶manufacturer data的见妒。

  func peripheralManager(_ peripheral: CBPeripheralManager, central: CBCentral,
    didSubscribeTo characteristic: CBCharacteristic) {
    guard characteristic == textCharacteristic else { return }
    prepareDataAndSend()
  }

  func prepareDataAndSend() {
    guard let data = textView.text.data(using: .utf8) else { return }
    self.dataToSend = data
    sendDataIndex = 0
    sendData()
  }

func sendData() {
    if sendingEOM {
      let didSend = peripheralManager.updateValue("EOM".data(using: .utf8)!, for: textCharacteristic, onSubscribedCentrals: nil)
      if didSend {
        sendingEOM = false
        print("Sent: EOM")
      }
      return
    }
    let numberOfBytes = (dataToSend as NSData).length
    guard sendDataIndex < numberOfBytes else { return }
    var didSend = true
    while didSend {
      var amountToSend = numberOfBytes - sendDataIndex
      if amountToSend > notifyMTU {
        amountToSend = notifyMTU
      }

      let chunk = dataToSend.withUnsafeBytes{(body: UnsafePointer<UInt8>) in
        return Data(
          bytes: body + sendDataIndex,
          count: amountToSend
        )
      }
      didSend = peripheralManager.updateValue(chunk, for: textCharacteristic, onSubscribedCentrals: [])
      if !didSend { return }

      guard let stringFromData = String(data: chunk, encoding: .utf8) else { return }
      print("Sent: \(stringFromData)")
      sendDataIndex += amountToSend
      if sendDataIndex >= dataToSend.count {
        sendingEOM = true
        let eomSent = peripheralManager.updateValue("EOM".data(using: .utf8)!, for: textCharacteristic, onSubscribedCentrals: nil)
        if eomSent {
          sendingEOM = false
          print("Sent: EOM")
        }
        return
      }
    }
  }

此回調(diào)會(huì)在中央設(shè)備訂閱了當(dāng)初廣播的characteristic時(shí)調(diào)用，這里我們準(zhǔn)備發(fā)送數(shù)據(jù)甸陌，發(fā)送數(shù)據(jù)的過(guò)程中和中央設(shè)備需要約定一個(gè)標(biāo)識(shí)表明數(shù)據(jù)是否發(fā)送完畢须揣，這里采用了EOM標(biāo)志作為結(jié)束位，采用二進(jìn)制流的形式進(jìn)行發(fā)送钱豁。

  func peripheralManagerIsReady(toUpdateSubscribers peripheral: CBPeripheralManager) {
    sendData()
  }

此回調(diào)在CBPeripheralManager準(zhǔn)備發(fā)送下一段數(shù)據(jù)時(shí)發(fā)送耻卡，這里一般用來(lái)實(shí)現(xiàn)保證分段數(shù)據(jù)按順序發(fā)送給中央設(shè)備。

  func peripheralManager(_ peripheral: CBPeripheralManager, didReceiveWrite requests: [CBATTRequest]) {
    guard let request = requests.first, request.characteristic == mapCharacteristic else {
      peripheral.respond(to: requests.first!, withResult: .attributeNotFound)
      return
    }
    map() { locationManager?.stopUpdatingLocation() }
    peripheral.respond(to: request, withResult: .success)
  }

  fileprivate func map(completionHandler: () -> Void) {
    locationManager = CLLocationManager()
    locationManager?.delegate = self
    locationManager?.desiredAccuracy = kCLLocationAccuracyBest
    locationManager?.requestWhenInUseAuthorization()
    if CLLocationManager.authorizationStatus() == .authorizedWhenInUse || CLLocationManager.authorizationStatus() == .authorizedAlways {
      locationManager?.startUpdatingLocation()
    }
  }

此回調(diào)在中央設(shè)備針對(duì)響應(yīng)的characteristic發(fā)送數(shù)據(jù)給外圍設(shè)備時(shí)調(diào)用牲尺，這里我們模擬中央設(shè)備發(fā)送打開(kāi)地圖的指令給iPhone卵酪。

CBCentralManager

新建一個(gè)CentralViewController類(lèi)并繼承UIViewController，定義成員變量centralManager并初始化，同時(shí)設(shè)置代理溃卡，由于篇幅有限這里只貼出關(guān)鍵代碼：

centralManager = CBCentralManager(delegate: self, queue: nil)

Central Manager delegate

代理必須要實(shí)現(xiàn)的方法如下：

  func centralManagerDidUpdateState(_ central: CBCentralManager) {
    switch central.state {
    case .poweredOn: scan()
    case .poweredOff, .resetting: cleanup()
    default: return
    }
  }

  func scan() {
    centralManager.scanForPeripherals(withServices: [TextOrMapServiceUUID], options: [CBCentralManagerScanOptionAllowDuplicatesKey: NSNumber(value: true as Bool)])
  }

  func cleanup() {
    guard discoveredPeripheral?.state != .disconnected,
      let services = discoveredPeripheral?.services else {
        centralManager.cancelPeripheralConnection(discoveredPeripheral!)
        return
    }
    for service in services {
      if let characteristics = service.characteristics {
        for characteristic in characteristics {
          if characteristic.uuid.isEqual(textCharacteristicUUID) {
            if characteristic.isNotifying {
              discoveredPeripheral?.setNotifyValue(false, for: characteristic)
              return
            }
          }
        }
      }
    }
    centralManager.cancelPeripheralConnection(discoveredPeripheral!)
  }

藍(lán)牙可用時(shí)開(kāi)始掃描溢豆，通過(guò)UUID掃描外圍設(shè)備廣播的服務(wù)。

  func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
    guard RSSI_range.contains(RSSI.intValue) && discoveredPeripheral != peripheral else { return }
    discoveredPeripheral = peripheral
    centralManager.connect(peripheral, options: [:])
  }

需要檢查RSSI強(qiáng)度塑煎，只有藍(lán)牙信號(hào)強(qiáng)度在一定范圍內(nèi)才開(kāi)始嘗試進(jìn)行連接沫换。

 func centralManager(_ central: CBCentralManager, didFailToConnect peripheral: CBPeripheral, error: Error?) {
    if let error = error { print(error.localizedDescription) }
    cleanup()
  }

  func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    centralManager.stopScan()
    data.removeAll()
    peripheral.delegate = self
    peripheral.discoverServices([TextOrMapServiceUUID])
  }

  func centralManager(_ central: CBCentralManager, didDisconnectPeripheral peripheral: CBPeripheral, error: Error?) {
    if (peripheral == discoveredPeripheral) {
      cleanup()
    }
    scan()
  }

以上是關(guān)于連接的幾個(gè)回調(diào)函數(shù)，連接成功后就停止掃描最铁，然后調(diào)用peripheral.discoverServices方法讯赏，這會(huì)來(lái)到Peripheral Delegate中的相應(yīng)代理方法。

Peripheral Delegate

  func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
    if let error = error {
      print(error.localizedDescription)
      cleanup()
      return
    }

    guard let services = peripheral.services else { return }
    for service in services {
      peripheral.discoverCharacteristics([textCharacteristicUUID, mapCharacteristicUUID], for: service)
    }
  }

  func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
    if let error = error {
      print(error.localizedDescription)
      cleanup()
      return
    }

    guard let characteristics = service.characteristics else { return }
    for characteristic in characteristics {
      if characteristic.uuid == textCharacteristicUUID {
        textCharacteristic = characteristic
        peripheral.setNotifyValue(true, for: characteristic)
      } else if characteristic.uuid == mapCharacteristicUUID {
        mapCharacteristic = characteristic
      }
    }
  }

此回調(diào)用來(lái)發(fā)現(xiàn)services冷尉，實(shí)際開(kāi)發(fā)中這里可能用列表展示發(fā)現(xiàn)的服務(wù)漱挎，讓用戶(hù)進(jìn)行相應(yīng)的選擇。

  func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
    if let error = error {
      print(error.localizedDescription)
      return
    }

    if characteristic == textCharacteristic {
      guard let newData = characteristic.value else { return }
      let stringFromData = String(data: newData, encoding: .utf8)

      if stringFromData == "EOM" {
        textView.text = String(data: data, encoding: .utf8)
        data.removeAll()
      } else {
        data.append(newData)
      }
    }
  }

此回調(diào)對(duì)應(yīng)peripheralManager.updateValue這個(gè)方法雀哨，能拿到外圍設(shè)備發(fā)送過(guò)來(lái)的數(shù)據(jù)磕谅。

 func peripheral(_ peripheral: CBPeripheral, didUpdateNotificationStateFor characteristic: CBCharacteristic, error: Error?) {
    if let error = error { print(error.localizedDescription) }
    guard characteristic.uuid == textCharacteristicUUID else { return }
    if characteristic.isNotifying {
      print("Notification began on \(characteristic)")
    } else {
      print("Notification stopped on \(characteristic). Disconnecting...")
    }
  }

此回調(diào)處理外圍設(shè)備的characteristic通知，比如下線(xiàn)或者離開(kāi)的情況雾棺，這里進(jìn)行簡(jiǎn)單的打印膊夹。

總結(jié)

對(duì)藍(lán)牙開(kāi)發(fā)中的外圍設(shè)備，中央設(shè)備捌浩，UUID放刨，service和characteristic等基本概念進(jìn)行了簡(jiǎn)單介紹，并利用Core Bluetooth 框架進(jìn)行了簡(jiǎn)單的demo演示尸饺，主要是需要理解幾個(gè)特定代理方法即可进统，同時(shí)由于iOS的限制，iPhone在作為外設(shè)時(shí)在廣播的時(shí)候是不能發(fā)送額外數(shù)據(jù)的浪听，這點(diǎn)需要注意螟碎。