BluetoothLeScanner could not find callback wrapper

Question

Because of I had problems with Bluetooth on Android Lollipop, I have tried to change the scanner method.
So I have tried to use the new package. In the previous version

Answer 1

The log message D/BluetoothLeScanner: could not find callback wrapper appears whenever Android's bluetooth scanning APIs are told top stop scanning for an app when they think scanning has not started. You can see this by looking at the source code of Android's BluetoothLeScanner here.

This is usually safe to ignore as there are lot of reasons that scanning my not have actually started (it was already stopped, bluetooth is off, permissions have not been granted, etc.) Client software that does scanning often stops scanning on a timer regardless of whether it has been successfully started, or whether it was manually stopped before the timer goes off. Android's example code (and the code shown above) does exactly this, often causing these log messages to show up.

If you really want to minimize these messages, you need to keep track of whether scanning actually started and only stop scanning if it actually did. Unfortunately, you don't get a return code if scanning starts successfully, and you only get an asynchronous callback to onScanFailed(errorCode) if you cannot start successfully. So one approach would be to set scanStartCount++; when you call start scan, and set scanStartCount--; when you get a callback to onScanFailed(errorCode). Then when your timer goes off to stop the scan, only actually stop it if the scanStartCount > 0.

Keep in mind that you can only minimize these messages coming from your application. Other applications on the phone doing bluetooth scanning may be causing these messages to be emitted as well.