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Open discussion about Android BLE & new Android O service limitations

Chris (Your digital co-driver)

by German autolabs GmbH

Current app state & challenges

  • 💯% Kotlin (Yay!!!)
  • MVP Architecture
  • Dagger for Dependency injection
  • RxJava2 to wire-up different layers
  • Separated modules as Google likes!
  • Firebase
  • one MainService background service that handles events (Calls, SMS, Calendar, eMail, and etc.)
  • Protobuf protocol over BLE for smaller data transfer on BLE connection
  • currently using RxAndroidBle library

some BLE terms you can study more about here...

https://developer.android.com/guide/topics/connectivity/bluetooth-le.html

  • GATT: The GATT profile is a general specification for sending and receiving short pieces of data known as "attributes" over a BLE link.
  • ATT: GATT is built on top of the Attribute Protocol.
  • Characteristic: A characteristic contains a single value and 0-n descriptors that describe the characteristic’s value.
  • Service: A service is a collection of characteristics.
  • UUID!

Learnings from real world BLE

  • BLE @ SumUp : 300k active installs
  • Murphy’s Law applies
  • Disconnecting is your best friend
  • #samsungwtf

Device Discovery

  • General Idea: Scan for Service UUID
  • API Level < 21 : BluetoothAdapter.startLeScan()
    • :(
  • API Level > 21: BluetoothAdapter.getBluetoothLeScanner()
    • Yay!
  • But: Both have issues

Advice on Scanning with

  • startLeScan()
    • Do on main thread
    • Because #samsungwtf
    • Requires you to call stopLeScan()
    • Does not actually stop immediately
  • getBluetoothLeScanner()
    • Do asynchronous (HandlerThread)
    • SCAN_FAILED_APPLICATION_REGISTRATION_FAILED

Making contact

  • Connect to device UUID
    • Might not work
    • Might not be your fault
    • Might be slow
      • Very slow
    • → Timeouts!
  • Don’t confuse the stack
    • Async
    • Queue
    • Decouple
    • When in doubt, reconnect
    • Or even re-run discovery
    • Or... use a library :)
  • Analytics!
    • Measure performance
    • Log to your backend
    • Create statistics
    • Analyze & Improve

Questions (open mic):

  • What're your experiences with Android BLE?
  • What're considerations that we should take care of API below 21?

AFAIK there is a new background service limitation in Android Oreo:

  • Is there any way to keep background service running on Android Oreo? (without using foreground services!!!)
  • Could BLE wake up my app background service?
  • Is there any suggestion for waking my service to serve user when he gets into the car and finds the Chris device?