Develop Reference

Android CompanionDeviceManager Never Finds Any Nearby Bluetooth Devices

UPDATE: Added Main Activity code which contains Bluetooth permissions logic
I'm trying to utilize Android's CompanionDeviceManager API to find nearby bluetooth (non LE) devices on my Pixel 5 running Android 13, but it only ever seems to find nearby WiFi networks. I'm suspicious that the deviceFilter isn't working properly.
Initially, my code to configure the BluetoothDeviceFilter looked like this:
private val deviceFilter: BluetoothDeviceFilter = BluetoothDeviceFilter.Builder()
// Match only Bluetooth devices whose name matches the pattern
.setNamePattern(Pattern.compile("(?i)\\b(Certain Device Name)\\b"))
.build()
private val pairingRequest: AssociationRequest = AssociationRequest.Builder()
// Find only devices that match our request filter
.addDeviceFilter(deviceFilter)
// Don't stop scanning as soon as one device matching the filter is found.
.setSingleDevice(false)
.build()
With this code, however, no devices ever appear within the system generated Companion Device Pairing screen. The spinner spins until timeout
Thinking maybe my regex was unintentionally too restrictive, I changed the filter to use a regexp that allows everything, like so:
.setNamePattern(Pattern.compile(".*"))
But even this filter fails to allow any nearby bluetooth devices to appear in the Pairing screen.
When I intentionally don't add any filter all I see are WiFi networks, so the Companion Device Manager can work, it's just seemingly misconfigured for Bluetooth results.
private val pairingRequest: AssociationRequest = AssociationRequest.Builder()
// No filter, let's see it all!
.setSingleDevice(false)
.build()
Using the Android OS's system Bluetooth menu I clearly see there are Bluetooth devices within range of my device, and I can even connect to them, but the same devices never appear within my app.
What am I doing wrong that's causing no nearby Bluetooth devices to appear in my CompanionDeviceManager Pairing Screen?
Code below:
HomeFragment.kt
class HomeFragment : Fragment() {
//Filter visible Bluetooth devices so only Mozis within range are displayed
private val deviceFilter: BluetoothDeviceFilter = BluetoothDeviceFilter.Builder()
// Match only Bluetooth devices whose name matches the pattern.
.setNamePattern(Pattern.compile(BLUETOOTH_DEVICE_NAME_REGEX_TO_FILTER_FOR))
.build()
private val pairingRequest: AssociationRequest = AssociationRequest.Builder()
// Find only devices that match this request filter.
.addDeviceFilter(deviceFilter)
// Don't stop scanning as soon as one device matching the filter is found.
.setSingleDevice(false)
.build()
private val deviceManager: CompanionDeviceManager by lazy {
requireContext().getSystemService(Context.COMPANION_DEVICE_SERVICE) as CompanionDeviceManager
}
private val executor: Executor = Executor { it.run() }
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
setupPairingButton()
}
/**
* This callback listens for the result of connection attempts to our Mozi Bluetooth devices
*/
#Deprecated("Deprecated in Java")
#SuppressLint("MissingPermission")
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
when (requestCode) {
SELECT_DEVICE_REQUEST_CODE -> when (resultCode) {
Activity.RESULT_OK -> {
// The user chose to pair the app with a Bluetooth device.
val deviceToPair: BluetoothDevice? =
data?.getParcelableExtra(CompanionDeviceManager.EXTRA_DEVICE)
deviceToPair?.createBond()
}
}
else -> super.onActivityResult(requestCode, resultCode, data)
}
}
private fun setupPairingButton() {
binding.buttonPair.setOnClickListener {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
/**
* This is the approach to show a pairing dialog for Android 33+
*/
deviceManager.associate(pairingRequest, executor,
object : CompanionDeviceManager.Callback() {
// Called when a device is found. Launch the IntentSender so the user
// can select the device they want to pair with
override fun onAssociationPending(intentSender: IntentSender) {
intentSender.let { sender ->
activity?.let { fragmentActivity ->
startIntentSenderForResult(
fragmentActivity,
sender,
SELECT_DEVICE_REQUEST_CODE,
null,
0,
0,
0,
null
)
}
}
}
override fun onAssociationCreated(associationInfo: AssociationInfo) {
// Association created.
// AssociationInfo object is created and get association id and the
// macAddress.
var associationId = associationInfo.id
var macAddress: MacAddress? = associationInfo.deviceMacAddress
}
override fun onFailure(errorMessage: CharSequence?) {
// Handle the failure.
showBluetoothErrorMessage(errorMessage)
}
})
} else {
/**
* This is the approach to show a pairing dialog for Android 32 and below
*/
// When the app tries to pair with a Bluetooth device, show the
// corresponding dialog box to the user.
deviceManager.associate(
pairingRequest,
object : CompanionDeviceManager.Callback() {
override fun onDeviceFound(chooserLauncher: IntentSender) {
startIntentSenderForResult(
chooserLauncher,
SELECT_DEVICE_REQUEST_CODE,
null,
0,
0,
0,
null
)
}
override fun onFailure(error: CharSequence?) {
// Handle the failure.
showBluetoothErrorMessage(error)
}
}, null
)
}
}
}
companion object {
private const val SELECT_DEVICE_REQUEST_CODE = 0
private const val BLUETOOTH_DEVICE_NAME_REGEX_TO_FILTER_FOR = "(?i)\\bCertain Device Name\\b"
}}
MainActivity.kt
class MainActivity : AppCompatActivity() {
private val enableBluetoothIntent = Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE)
private var bluetoothEnableResultLauncher =
registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
binding.loadingSpinner.hide()
when (result.resultCode) {
Activity.RESULT_OK -> {
Snackbar.make(
binding.root,
resources.getString(R.string.bluetooth_enabled_lets_pair_with_your_mozi),
Snackbar.LENGTH_SHORT
).show()
}
Activity.RESULT_CANCELED -> {
Snackbar.make(
binding.root,
getString(R.string.without_bluetooth_you_cant_pair_with_your_mozi),
Snackbar.LENGTH_INDEFINITE
)
.setAction(resources.getString(R.string._retry)) {
ensureBluetoothIsEnabled()
}
.show()
}
}
}
private val requestBluetoothPermissionLauncher =
registerForActivityResult(
ActivityResultContracts.RequestPermission()
) { isGranted: Boolean ->
if (isGranted) {
bluetoothEnableResultLauncher.launch(enableBluetoothIntent)
} else {
// Explain to the user that the feature is unavailable because the
// feature requires a permission that the user has denied. At the
// same time, respect the user's decision. Don't link to system
// settings in an effort to convince the user to change their
// decision.
Snackbar.make(
binding.root,
getString(R.string.without_bluetooth_you_cant_pair_with_your_mozi),
Snackbar.LENGTH_INDEFINITE
)
.setAction(resources.getString(R.string._retry)) {
ensureBluetoothIsEnabled()
}
.show()
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setupViews()
ensureBluetoothIsEnabled()
}
private fun setupViews() {
//Here we setup the behavior of the button in our rationale dialog: basically we need to
// rerun the permissions check logic if it was already denied
binding.bluetoothPermissionsRationaleDialogButton.setOnClickListener {
binding.permissionsRationaleDialog.animateShow(false)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
requestBluetoothPermissionLauncher.launch(Manifest.permission.BLUETOOTH_CONNECT)
} else {
requestBluetoothPermissionLauncher.launch(Manifest.permission.BLUETOOTH)
}
}
}
private fun ensureBluetoothIsEnabled() {
binding.loadingSpinner.show()
val bluetoothManager: BluetoothManager = getSystemService(BluetoothManager::class.java)
val bluetoothAdapter: BluetoothAdapter? = bluetoothManager.adapter
if (bluetoothAdapter == null) {
// Device doesn't support Bluetooth
binding.loadingSpinner.hide()
Snackbar.make(
binding.root,
resources.getString(R.string.you_need_a_bluetooth_enabled_device),
Snackbar.LENGTH_INDEFINITE
).show()
}
if (bluetoothAdapter?.isEnabled == false) {
// Check if Bluetooth permissions have been granted before we try to enable the
// device
if (ActivityCompat.checkSelfPermission(
this,
Manifest.permission.BLUETOOTH_CONNECT //TODO: test if this needs variant for legacy devices
) != PackageManager.PERMISSION_GRANTED
) {
/**
* We DON'T have Bluetooth permissions. We have to get them before we can ask the
* user to enable Bluetooth
*/
binding.loadingSpinner.hide()
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
if (shouldShowRequestPermissionRationale(Manifest.permission.BLUETOOTH_CONNECT)) {
binding.permissionsRationaleDialog.animateShow(true)
} else {
requestBluetoothPermissionLauncher.launch(Manifest.permission.BLUETOOTH_CONNECT)
}
} else {
if (shouldShowRequestPermissionRationale(Manifest.permission.BLUETOOTH)) {
binding.permissionsRationaleDialog.animateShow(true)
} else {
requestBluetoothPermissionLauncher.launch(Manifest.permission.BLUETOOTH)
}
}
return
} else {
/**
* We DO have Bluetooth permissions. Now let's prompt the user to enable their
* Bluetooth radio
*/
binding.loadingSpinner.hide()
bluetoothEnableResultLauncher.launch(enableBluetoothIntent)
}
} else {
/**
* Bluetooth is enabled, we're good to continue with normal app flow
*/
binding.loadingSpinner.hide()
}
}
}
Android Manifest
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<!-- Bluetooth Permissions -->
<uses-feature android:name="android.software.companion_device_setup" android:required="true"/>
<uses-feature android:name="android.hardware.bluetooth" android:required="true"/>
<!-- Request legacy Bluetooth permissions on older devices. -->
<uses-permission android:name="android.permission.BLUETOOTH"
android:maxSdkVersion="30" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"
android:maxSdkVersion="30" />
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
<!-- Needed only if your app looks for Bluetooth devices.
If your app doesn't use Bluetooth scan results to derive physical
location information, you can strongly assert that your app
doesn't derive physical location. -->
<uses-permission android:name="android.permission.BLUETOOTH_SCAN"
android:usesPermissionFlags= "neverForLocation"
tools:targetApi="s" />
<uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" />
...
</manifest>

You could try using an empty BluetoothDeviceFilter like this:
private val deviceFilter: BluetoothDeviceFilter = BluetoothDeviceFilter.Builder().build()
to signal to the API that you want Bluetooth devices, and see if at least the phone sees your device.
Then you could try again with the name filter, this time adding a service UUID filter with BluetoothDeviceFilter.Builder.addServiceUuid.
If you don't know the UUID of your device or don't want to use it as a filter, you can use an arbitrary one and set the mask to all zeros (the docs suggest that it might also work using null values).
This is a hackish solution, but it might help you move a step further

It might be a permission issue.
In the docs, I read:
The BLUETOOTH_ADVERTISE, BLUETOOTH_CONNECT, and BLUETOOTH_SCAN permissions are runtime permissions. Therefore, you must explicitly request user approval in your app before you can look for Bluetooth devices, make a device discoverable to other devices, or communicate with already-paired Bluetooth devices.
So you could to add the following code in your HomeFragment class:
private val requestMultiplePermissions = registerForActivityResult(ActivityResultContracts.RequestMultiplePermissions()) { permissions ->
permissions.entries.forEach {
Log.d("Permission Request", "${it.key} = ${it.value}")
}
}
private val requestBluetooth = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
if (result.resultCode == RESULT_OK) {
// granted
} else {
// denied
}
}
and in the onCreateView method:
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
requestMultiplePermissions.launch(arrayOf(
Manifest.permission.BLUETOOTH_SCAN,
Manifest.permission.BLUETOOTH_CONNECT
))
} else {
val enableBtIntent = Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE)
requestBluetooth.launch(enableBtIntent)
}
to request the permissions at runtime.

The documentation does not mention it, but it appears that even with the CompanionDeviceManager the location access must be enabled on the device.
The app does not need the location permission anymore, but it must be enabled.

Android App receives 2 connections from the same device (nRF Module)

I have an android app which scans and connects to a predefined device name. My peripheral is an nRF module which is sending an incrementing data at 1Hz.
However, when I launch the app, it scans and logs multiple connections to the same device and consequently the values received duplicated values. So if there is a log for 3 connections then I get 3 duplicate values and 2 duplicates if there are 2 connections.
D/BluetoothGatt: onClientConnectionState() - status=0 clientIf=14 device=FD:72:38:AA:1A:E7
I/BLE log: Connected to device FD:72:38:AA:1A:E7
D/BluetoothGatt: onClientConnectionState() - status=0 clientIf=15 device=FD:72:38:AA:1A:E7
I/BLE log: Connected to device FD:72:38:AA:1A:E7
Here is my code:
Scanning:
private fun bleScan() {
val scanFilter = ScanFilter.Builder()
.setDeviceName("VEGA-TEST")
.build()
val scanSettings = ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.build()
bleScanner.startScan(mutableListOf(scanFilter), scanSettings, object : ScanCallback() {
override fun onScanResult(callbackType: Int, result: ScanResult) {
super.onScanResult(callbackType, result)
with(result.device) {
Log.i("BLE log", "Found device $address")
connectGatt(this#BluetoothService, false ,gattCallback)
}
}
})
}
GATT Connections
private val gattCallback = object : BluetoothGattCallback() {
override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
super.onConnectionStateChange(gatt, status, newState)
val deviceAddr = gatt.device.address
if(status == BluetoothGatt.GATT_SUCCESS) {
when(newState) {
BluetoothProfile.STATE_CONNECTED -> {
Log.i("BLE log", "Connected to device $deviceAddr")
bleStopScan()
Handler(Looper.getMainLooper()).post {
gatt.discoverServices()
}
}
BluetoothProfile.STATE_DISCONNECTED -> {
Log.i("BLE log", "Disconnected from device $deviceAddr")
}
else -> {
Log.i("BLE log", "Hit event $newState")
}
}
} else {
Log.e("BLE log", "BLE error $status for $deviceAddr")
}
}
override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
super.onServicesDiscovered(gatt, status)
with(gatt) {
Log.i("BLE log","Discovered ${services.size} services for ${device.address}")
printGattTable()
enableNotification(gatt)
}
}
}
On the NRF Side i am sending data using a timer
static void txTimer_hander(void *p_context){
//TODO: Handle timeout
// SEND data to Device
//NRF_LOG_INFO("Timer : %d", tx_Data);
memset(val, 0, 7);
if(tx_Data < 50){
// SEND this Data
uint16_t now_data = tx_Data;
val[0] = 0xFF;
val[5] = now_data;
//memcpy(&val[0], (uint16_t*)0xFF, 1);
//memcpy(&val[6], &now_data, 2);
//val[0] = now_data;
//
tx_Data++;
}else{
tx_Data = 0;
// SEND this Data
uint16_t now_data = tx_Data;
//memcpy(&val[0], (uint16_t*)0xFF, 1);
val[0] = 0xFF;
val[5] = now_data;
//memcpy(&val[6], &now_data, 2);
//
tx_Data++;
}
NRF_LOG_INFO("Sending %d", tx_Data);
send_nus_data(val, 7);
}
NOTE I am using Android 12 and testing using Android Studio
I would appreciate any help!
Thanks

If your phone catches two advertisement packets, it will create two logical connections. You should check before you call connectGatt if you have already called connectGatt, and if so don't connect again. You should also stop the scan if you don't need the scan to continue when you have already found a device.

How to detect Android Auto is connected with Android 12

In my driving-companion app, I have a need to detect the state of Android Auto. For several years now, I've been using UiModeManager to get the current state at startup and a BroadcastReceiver to detect state changes while the app is running. This has always worked perfectly, until Android 12. With Android 12, UiModeManager always reports UI_MODE_TYPE_NORMAL, even when Android Auto is connected and active, and my BroadcastReceiver is never called after connecting or disconnecting.
This is my code for detecting state at startup:
inCarMode = uiModeManager.getCurrentModeType() == Configuration.UI_MODE_TYPE_CAR;
and this is my BroadcastReceiver setup:
IntentFilter carModeFilter = new IntentFilter();
carModeFilter.addAction(UiModeManager.ACTION_ENTER_CAR_MODE);
carModeFilter.addAction(UiModeManager.ACTION_EXIT_CAR_MODE);
registerReceiver(carModeReceiver, carModeFilter);
Again, this has always worked perfectly with Android 5 through Android 11. Is this a bug in Android 12, or is there some new way to detect Android Auto state in Android 12?

You need to use the CarConnection API documented here

Configuration.UI_MODE_TYPE_CAR is not working on Anroid 12. As #Pierre-Olivier Dybman said, you can use CarConnection API in the androidx.car.app:app library. But that is too heavy to import entire library only for car connections if you don't need other features.
So I write a piece of code base on the CarConnection to detect Android Auto connection, as below:
class AutoConnectionDetector(val context: Context) {
companion object {
const val TAG = "AutoConnectionDetector"
// columnName for provider to query on connection status
const val CAR_CONNECTION_STATE = "CarConnectionState"
// auto app on your phone will send broadcast with this action when connection state changes
const val ACTION_CAR_CONNECTION_UPDATED = "androidx.car.app.connection.action.CAR_CONNECTION_UPDATED"
// phone is not connected to car
const val CONNECTION_TYPE_NOT_CONNECTED = 0
// phone is connected to Automotive OS
const val CONNECTION_TYPE_NATIVE = 1
// phone is connected to Android Auto
const val CONNECTION_TYPE_PROJECTION = 2
private const val QUERY_TOKEN = 42
private const val CAR_CONNECTION_AUTHORITY = "androidx.car.app.connection"
private val PROJECTION_HOST_URI = Uri.Builder().scheme("content").authority(CAR_CONNECTION_AUTHORITY).build()
}
private val carConnectionReceiver = CarConnectionBroadcastReceiver()
private val carConnectionQueryHandler = CarConnectionQueryHandler(context.contentResolver)
fun registerCarConnectionReceiver() {
context.registerReceiver(carConnectionReceiver, IntentFilter(ACTION_CAR_CONNECTION_UPDATED))
queryForState()
}
fun unRegisterCarConnectionReceiver() {
context.unregisterReceiver(carConnectionReceiver)
}
private fun queryForState() {
carConnectionQueryHandler.startQuery(
QUERY_TOKEN,
null,
PROJECTION_HOST_URI,
arrayOf(CAR_CONNECTION_STATE),
null,
null,
null
)
}
inner class CarConnectionBroadcastReceiver : BroadcastReceiver() {
// query for connection state every time the receiver receives the broadcast
override fun onReceive(context: Context?, intent: Intent?) {
queryForState()
}
}
internal class CarConnectionQueryHandler(resolver: ContentResolver?) : AsyncQueryHandler(resolver) {
// notify new queryed connection status when query complete
override fun onQueryComplete(token: Int, cookie: Any?, response: Cursor?) {
if (response == null) {
Log.w(TAG, "Null response from content provider when checking connection to the car, treating as disconnected")
notifyCarDisconnected()
return
}
val carConnectionTypeColumn = response.getColumnIndex(CAR_CONNECTION_STATE)
if (carConnectionTypeColumn < 0) {
Log.w(TAG, "Connection to car response is missing the connection type, treating as disconnected")
notifyCarDisconnected()
return
}
if (!response.moveToNext()) {
Log.w(TAG, "Connection to car response is empty, treating as disconnected")
notifyCarDisconnected()
return
}
val connectionState = response.getInt(carConnectionTypeColumn)
if (connectionState == CONNECTION_TYPE_NOT_CONNECTED) {
Log.i(TAG, "Android Auto disconnected")
notifyCarDisconnected()
} else {
Log.i(TAG, "Android Auto connected")
notifyCarConnected()
}
}
}
}
This solution works on android 6~12. If you need to detect car connection status on android 5, use the Configuration.UI_MODE_TYPE_CAR solution.

Unable to run ble scanner when screen is locked

Am running a foreground service to scan ble devices which is working fine when the phone is not locked. But when the phone is locked, the scanner is unable to detect any devices near by. The scanned count is always 0 when the phone is locked. I have also added the filter for my scanner but still no fortune. Looking for some help.
//adding filters of the manufacturer and the uuid
fun startScan(){
settings = ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.build()
val builder = ScanFilter.Builder()
builder.setManufacturerData(0x004c, byteArrayOf())
val manufactureFilter= builder.build()
val uuidBuilder = ScanFilter.Builder()
val serviceUuidString = "f8c62883-xxxx-xxxx-xxxx-430326af8bd0"
val serviceUuidMaskString = "FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF"
val parcelUuid: ParcelUuid = ParcelUuid.fromString(serviceUuidString)
val parcelUuidMask: ParcelUuid = ParcelUuid.fromString(serviceUuidMaskString)
uuidBuilder.setServiceUuid(parcelUuid, parcelUuidMask)
val uuidFilter = uuidBuilder.build()
filters = ArrayList<ScanFilter>()
filters.add(manufactureFilter)
filters.add(uuidFilter)
scanLeDevice(true)
}
//to start the ble scan for a short period
fun scanLeDevice(enable: Boolean) {
if (enable) {
Log.i(TAG, "Scanning started")
if(beaconCollectionTimer != null){
beaconCollectionTimer?.cancel()
}
beaconCollectionTimer = Timer()
beaconCollectionTimer?.schedule(object : TimerTask(){
override fun run() {
scanLeDevice(false)
}
}, SCANNING_INTERVEL)
bluetoothAdapter.getBluetoothLeScanner()
.startScan(filters, settings, mScanCallback)
} else {
Log.i(TAG, "scanning stopped")
if (bluetoothAdapter.getBluetoothLeScanner() != null) {
bluetoothAdapter.getBluetoothLeScanner().stopScan(mScanCallback)
}
isScanning = false
}
}

After trying various libraries to get my scanner work properly, I realized that the issue is not in the code but with the battery saver. All I did is removed the app from the battery optimization apps list and my scanner started working as expected. Even after the screen is locked am able to run the bleScanner and detect the near by devices.

Android ble: Unable to send large data

I'm trying to implement an app for transfer some strings between ble devices (for now one device act as central and the other one as pheripheral) but without success.
This is how my peripheral (server) is set up.
Characteristic build
fun buildCharacteristic(
characteristicUUID: UUID,
): BluetoothGattCharacteristic {
var properties = BluetoothGattCharacteristic.PROPERTY_READ or
BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE or
BluetoothGattCharacteristic.PROPERTY_NOTIFY
var permission = BluetoothGattCharacteristic.PERMISSION_READ or
BluetoothGattCharacteristic.PERMISSION_WRITE
var characteristic = BluetoothGattCharacteristic(
characteristicUUID,
properties,
permission
)
return characteristic
}
service build
fun buildService(
serviceUUID: UUID,
serviceType: Int,
characteristics: List<BluetoothGattCharacteristic>
) {
bluetoothGattService = BluetoothGattService(
serviceUUID,
BluetoothGattService.SERVICE_TYPE_PRIMARY
)
for (characteristic in characteristics) {
bluetoothGattService.addCharacteristic(characteristic)
}
}
and this is how i start ble server (i omit implementation of callbacks)
fun startServer(
bleAdapter: BluetoothAdapter,
btManager: BluetoothManager,
context: Context
) {
bleAdvertiser = bleAdapter.bluetoothLeAdvertiser
bleGattServer = btManager.openGattServer(context, gattServerCallback)
bleGattServer.addService(bluetoothGattService)
var settings = AdvertiseSettings.Builder().apply {
setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_LOW_LATENCY)
setConnectable(true)
setTimeout(0)
setTxPowerLevel(AdvertiseSettings.ADVERTISE_TX_POWER_HIGH)
}
var data = AdvertiseData.Builder().apply {
setIncludeDeviceName(true)
}
bleAdvertiser.startAdvertising(settings.build(), data.build(), advertiseCallback)
}
On central (client) side, when onScanResult is triggered, i try to connect with device:
fun connectToDevice(device: BluetoothDevice) {
device.connectGatt(
context,
false,
createGattCallback()
)
}
where createGattCallback() is a function return a BluetoothGattCallback object. Inside this callback, when onConnectionStateChange is called, i call service discover, and when service is discovered i try do write data to peripheral
override fun onServicesDiscovered(gatt: BluetoothGatt?, status: Int) {
super.onServicesDiscovered(gatt, status)
if (gatt?.services != null) {
var serviceFound = false
for (service in gatt.services) {
if (service.uuid == Consts.SERVICE_UUID) {
serviceFound = true
var bluetoothGattCharacteristic = service.getCharacteristic(Consts.CHARACTERISTIC_UUID)
writeCharacteristic(
gatt,
bluetoothGattCharacteristic
)
}
}
if (!serviceFound) {
gatt.disconnect()
}
}
}
fun writeCharacteristic(
gatt: BluetoothGatt,
characteristic: BluetoothGattCharacteristic
) {
var toSendString = "A random string for testing purpose only"
var toSendByteArray = toSendString.toByteArray(Charsets.UTF_8)
val chunkSize = 18
val numberOfPackets = ceil(
(toSendByteArray.size).toDouble() / chunkSize.toDouble()
)
for (i in 0 until numberOfPackets.toInt()) {
var startIndex = i * chunkSize
var endIndex = if (startIndex + chunkSize <= toSendByteArray.size) {
startIndex + chunkSize
} else {
toSendByteArray.size
}
var packet = toSendByteArray.copyOfRange(startIndex, endIndex)
characteristic.value = packet
gatt.writeCharacteristic(characteristic)
Thread.sleep(250)
}
}
My code seems not workin, on peripheral i don't receive entire string, but only the first 18 bytes. Where i'm wrong?

You need to wait for onCharacteristicWrite before you can send the next value. See Android BLE BluetoothGatt.writeDescriptor() return sometimes false.
And your sleep won't solve anything.