Solution for BLE scan's SCAN_FAILED_APPLICATION_REGISTRATION_FAILED? - bluetooth-lowenergy

Question

My Android app scans BLE devices, and from a certain point it start to fails with error code 2 (ScanCallback.SCAN_FAILED_APPLICATION_REGISTRATION_FAILED). I'm using Nexus 9, 5.0.1 Lollipop.
This problem continued even after I relaunched the app, and when I restarted the Bluetooth service from Settings, I could finally get rid of the problem. But this problem is recurring, and I think I'm coding in a wrong way; BLE related APIs are new and there is few information.
Does anyone know a general solution for this error, preferably not requiring restart of the Bluetooth service? Even though this error code is documented in Android API reference, I don't know how to handle it properly.

Answer 1

When you got the error
SCAN_FAILED_APPLICATION_REGISTRATION_FAILED
You should disable the BluetoothAdapter
BluetoothAdapter.getDefaultAdapter().disable();
Disabling BluetoothAdapter, the event STATE_TURNING_OFF is fired. Once this event is fired, try to reconnect to the BluetoothAdapter:
case BluetoothAdapter.STATE_OFF:
Log.d(TAG, "bluetooth adapter turned off");
handler.postDelayed(new Runnable() {
#Override
public void run() {
Log.d(TAG, "bluetooth adapter try to enable");
BluetoothAdapter.getDefaultAdapter().enable();
}}, 500);
break;

Answer 2

It turns out that Bluetooth LE requires the following Android application permissions in AndroidManifest.xml:
<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<!--BLE scanning is commonly used to determine a user's location with Bluetooth LE beacons. -->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<!-- if your app targets API level 21 or higher. -->
<uses-feature android:name="android.hardware.location.gps" />
<!--app is available to BLE-capable devices only. -->
<uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>
Besides on main activity:
// onResume()
if (ContextCompat.checkSelfPermission(this.getApplicationContext(),
android.Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
} else {
ActivityCompat.requestPermissions(this, new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION},
REQUEST_LOCATION_ENABLE_CODE);
}

Answer 3

You should perform operations only success initialization of BT adapter.
To be sure that it is ready create intent filter:
val filter = IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED)
and broadcast receiver(you will perform action only if adapter is ready):
val broadcastReceiver = object: BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent?) {
val action = intent?.action
if (action != null && action == BluetoothAdapter.ACTION_STATE_CHANGED) {
val state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR)
when (state) {
BluetoothAdapter.STATE_ON -> {
if (bluetoothAdapter.isEnabled) {
//perform your task here
}
}
BluetoothAdapter.STATE_OFF -> {}
}
}
}
}
then register receiver:
registerReceiver(broadcastReceiver, filter)
and relaunch adapter(this part can be replaces with check):
bluetoothAdapter.disable()
bluetoothAdapter.enable()
DONE!

Answer 4

I had this happen to me today. While manually disabling and then enabling BT in the Android Settings did not fix this, I was able to get it working after only disabling it manually and then have the app that is affected by the issue enable BT.
The app then pops up an Android System message "An app is requesting permission to turn on BT" (I have a German UI, so it may be worded differently), and when I then press allow, the app finally has proper access to BT and this error no longer shows.
Sounds like a bug or something.