First things first: running OSX 10.10.4, iOS 4, Xcode 6.3.2, iPhone 6, Swift
Short story: I have a certain Bluetooth LE device here from which I want to receive notifications when values of a Characteristic change, e.g. by user input. Trying to subscribe to it does not succeed, but rather yields an error `Error Domain=CBATTErrorDomain Code=10 "The attribute could not be found."`
Long story: So, I have a BluetoothManager class in which I start scanning for Peripherals as soon as my `$CBCentralManager.state` is `.PoweredOn`. That's easy, I'm even a good citizen and scan specifically for those with the Service I want
centralManager.scanForPeripheralsWithServices([ServiceUUID], options: nil)
Hoping this will succeed, I implemented the following delegate method:
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
}
So moving along, we get to:
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)
}
Yupp, this succeeds, so I get the confirmation and start to discover the Service:
func centralManager(central: CBCentralManager!, didConnectPeripheral peripheral: CBPeripheral!) {
println("Connected \(peripheral.name)")
peripheral.delegate = self
println("connected to \(peripheral)")
peripheral.discoverServices([BluetoothConstants.MY_SERVICE_UUID])
}
Which also works, since that delegate method gets called as well:
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
}
}
}
And what do you know: the characteristic *gets* discovered!
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?
}
}
Now the console output up until here looks like this:
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
Hey! It says `updateNotification` is `false`. Where does that come from? Why, it's my callback for `setNotify...`:
func peripheral(peripheral: CBPeripheral!, didUpdateNotificationStateForCharacteristic characteristic: CBCharacteristic!, error: NSError!) {
println("updateNotification: \(characteristic.isNotifying)")
}
What gives? I told it to be notifying! Why isn't it notifying? Let's set a breakpoint in the line with the println and check out the error object:
(lldb) po error
Error Domain=CBATTErrorDomain Code=10 "The attribute could not be found." UserInfo=0x17026eac0 {NSLocalizedDescription=The attribute could not be found.}
OK, so this leaves me out of ideas. I wasn't able to finde relevant clues regarding that error code. The description itself I cannot fathom since I tried to set up the notification for a Characteristic that I discovered earlier, hence it *must* exist, right? Also, on Android it seems possible to subscribe for notifications, so I guess I can rule out problems with the device... or can I? Any clues regarding this are truly appreciated!
