订阅来自 CBCharacteristic 的通知不起作用

Question

首要任务：运行 OSX 10.10.4、iOS 4、Xcode 6.3.2、iPhone 6、Swift

简短的故事：我这里有一个蓝牙 LE 设备，我想在特性值发生变化时从该设备接收通知，例如通过用户输入。尝试订阅它不会成功，而是会产生错误Error Domain=CBATTErrorDomain Code=10 "The attribute could not be found."

长话短说：所以，我有一个 BluetoothManager 类，一旦我的$CBCentralManager.state 是.PoweredOn，我就开始扫描外围设备。这很容易，我什至是一个好公民，并且专门为那些拥有我想要的服务的人扫描

centralManager.scanForPeripheralsWithServices([ServiceUUID], options: nil)

希望这会成功，我实现了以下委托方法：

func centralManager(central: CBCentralManager!, didDiscoverPeripheral peripheral: CBPeripheral!, advertisementData: [NSObject : AnyObject]!, RSSI: NSNumber!) {

    if *this is a known device* {
        connectToPeripheral(peripheral)
        return
    }

    [...] // various stuff to make something a known device, this works
}

所以继续前进，我们得到：

func connectToPeripheral(peripheral: CBPeripheral) {
    println("connecting to \(peripheral.identifier)")

    [...] // saving the peripheral in an array along the way so it is being retained

    centralManager.connectPeripheral(peripheral, options: nil)
}

是的，这成功了，所以我得到确认并开始发现服务：

func centralManager(central: CBCentralManager!, didConnectPeripheral peripheral: CBPeripheral!) {        
    println("Connected \(peripheral.name)")

    peripheral.delegate = self

    println("connected to \(peripheral)")
    peripheral.discoverServices([BluetoothConstants.MY_SERVICE_UUID])
}

这也有效，因为该委托方法也被调用：

func peripheral(peripheral: CBPeripheral!, didDiscoverServices error: NSError!) {

    if peripheral.services != nil {
        for service in peripheral.services {
            println("discovered service \(service)")
            let serviceObject = service as! CBService

            [...] // Discover the Characteristic to send controls to, this works
            peripheral.discoverCharacteristics([BluetoothConstants.MY_CHARACTERISTIC_NOTIFICATION_UUID], forService: serviceObject)

           [...] // Some unneccessary stuff about command caches
        }
    }
}

你知道什么：特征被发现了！

func peripheral(peripheral: CBPeripheral!, didDiscoverCharacteristicsForService service: CBService!, error: NSError!) {
    for characteristic in service.characteristics {
        let castCharacteristic = characteristic as! CBCharacteristic

        characteristics.append(castCharacteristic) // Retaining the characteristic in an Array as well, not sure if I need to do this

        println("discovered characteristic \(castCharacteristic)")
        if *this is the control characteristic* {
            println("control")
        } else if castCharacteristic.UUID.UUIDString == BluetoothConstants.MY_CHARACTERISTIC_NOTIFICATION_UUID.UUIDString {
            println("notification")
            peripheral.setNotifyValue(true, forCharacteristic: castCharacteristic)
        } else {
            println(castCharacteristic.UUID.UUIDString) // Just in case
        }
        println("following properties:")

        // Just to see what we are dealing with
        if (castCharacteristic.properties & CBCharacteristicProperties.Broadcast) != nil {
            println("broadcast")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.Read) != nil {
            println("read")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.WriteWithoutResponse) != nil {
            println("write without response")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.Write) != nil {
            println("write")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.Notify) != nil {
            println("notify")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.Indicate) != nil {
            println("indicate")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.AuthenticatedSignedWrites) != nil {
            println("authenticated signed writes ")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.ExtendedProperties) != nil {
            println("indicate")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.NotifyEncryptionRequired) != nil {
            println("notify encryption required")
        }
        if (castCharacteristic.properties & CBCharacteristicProperties.IndicateEncryptionRequired) != nil {
            println("indicate encryption required")
        }

        peripheral.discoverDescriptorsForCharacteristic(castCharacteristic) // Do I need this?
    }
}

现在到这里的控制台输出如下所示：

connected to <CBPeripheral: 0x1740fc780, identifier = $FOO, name = $SomeName, state = connected>
discovered service <CBService: 0x170272c80, isPrimary = YES, UUID = $BAR>
[...]
discovered characteristic <CBCharacteristic: 0x17009f220, UUID = $BARBAR properties = 0xA, value = (null), notifying = NO>
control
following properties:
read
write
[...]
discovered characteristic <CBCharacteristic: 0x17409d0b0, UUID = $BAZBAZ, properties = 0x1A, value = (null), notifying = NO>
notification
following properties:
read
write
notify
[...]
discovered DescriptorsForCharacteristic
[]
updateNotification: false

嘿！它说updateNotification 是false。那是从哪里来的？为什么，这是我对setNotify... 的回调：

func peripheral(peripheral: CBPeripheral!, didUpdateNotificationStateForCharacteristic characteristic: CBCharacteristic!, error: NSError!) {

    println("updateNotification: \(characteristic.isNotifying)")
}

什么给了？我告诉它要通知！为什么不通知？让我们在 println 的行中设置一个断点并检查错误对象：

(lldb) po error
Error Domain=CBATTErrorDomain Code=10 "The attribute could not be found." UserInfo=0x17026eac0 {NSLocalizedDescription=The attribute could not be found.}

好的，所以这让我没有想法。我无法找到有关该错误代码的相关线索。描述本身我无法理解，因为我试图为我之前发现的特征设置通知，因此它必须存在，对吗？此外，在 Android 上似乎可以订阅通知，所以我想我可以排除设备问题......或者我可以吗？任何有关这方面的线索都非常感谢！

Answer 1

对我来说，问题是我正在使用另一个 Android 设备作为外围设备并且需要实现配置描述符。看这里： https://stackoverflow.com/a/25508053/599743

Answer 2

从制造商那里收到更多信息后，我收集到设备已连接并发送通知，而不管特性的通信通知状态如何。这意味着即使peripheral(_, didUpdateNotificationStateForCharacteristic, error) 告诉我特征没有通知，peripheral(_, didUpdateValueForCharacteristic, error) 也会在设备发送数据时被调用并传递数据。我之前没有实现那个回调，因为我没想到会在这种状态下发送数据。

所以基本上，我的问题似乎已经解决了。尽管如此，我仍然对设备的行为是否符合蓝牙 LE 规范感兴趣；我不了解那些较低级别的实现，但假设 Apple 出于某种原因编写了他们的文档，至少强烈暗示 Characteristic 状态的变化将在接收任何数据之前发生。

Answer 3

虽然这是一个老问题并且已经解决了，但我想提供我的输入和 cmets。

首先，BLE 外设负责定义其特征的行为。外设可以选择定义特性属性。 Apple 文档here 中列出了 Characteristic 的各种受支持属性。

现在让我们专注于您的问题，您正在尝试收听特征值更改但订阅失败。

• 我在您的代码中看到的问题是，无论特征是否支持它，都会进行订阅。仅在支持的情况下订阅特征。请参阅以下代码块，该代码块显示了如何识别特征支持的属性并基于它执行操作。

  func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
  
      // Check if characteristics found for service.
      guard let characteristics = service.characteristics, error == nil else {
          print("error: \(String(describing: error))")
          return
      }
  
      // Loop over all the characteristics found.
      for characteristic in characteristics {
          if characteristic.properties.contains([.notify, .notifyEncryptionRequired]) {
              peripheral.setNotifyValue(true, for: characteristic)
          } else if characteristic.properties.contains([.read]) {
              peripheral.readValue(for: characteristic)
          } else if characteristic.properties.contains([.write]) {
              // Perform write operation
          }
      }
  }
  

如果 Characteristic 支持 notify 属性并且您订阅了它。订阅成功后，将调用以下委托，您可以在其中验证订阅状态。

func peripheral(_ peripheral: CBPeripheral, didUpdateNotificationStateFor characteristic: CBCharacteristic, error: Error?) { 
    // Check subscription here
    print("isNotifying: \(characteristic.isNotifying)")
}

如果订阅成功，每当更新特征时，将使用新值调用以下委托方法。

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
    // read updated value for characteristic.
}

检查它是否不起作用

• 请与外围设备制造商核实特征实现以及它是否支持必要的属性。
• 检查您的实施并确保您遵循所有必要的步骤。

我已经尝试在各个方面尽可能地回答。希望能帮助到你。快乐编码:)