I'm trying to read a value from a custom characteristic in a custom service on a BLE device.
I successfully call the readCharcteristic method as it returns true. However, the onCharacteristicRead callback function is never invoked. I am unable to determine why this is so.
My read function is as follows (there is no pending or ongoing read or write request when this method if called) -
fun readOneSpecificCharacteristic() {
if (lpnInfoChar?.isReadable() == true) {
Log.i("READ", "READABLE")
if (btGatt?.readCharacteristic(lpnInfoChar) == true) {
Log.i("READ", "INIT SUCCESS") //<- my code reaches here
} else {
Log.i("READ", "INIT FAIL")
}
} else {
Log.i("READ", "NOT READABLE")
}
}
My Callback (which is never invoked) -
private val gattCallback = object: BluetoothGattCallback() {
override fun onCharacteristicRead(
gatt: BluetoothGatt,
characteristic: BluetoothGattCharacteristic,
value: ByteArray,
status: Int
) {
Log.i("Callback", "onCharacteristicRead")
with(characteristic) {
when (status) {
BluetoothGatt.GATT_SUCCESS -> {
Log.i("BluetoothGattCallback", "Read characteristic $uuid:\n${value.toHexString()}")
}
BluetoothGatt.GATT_READ_NOT_PERMITTED -> {
Log.e("BluetoothGattCallback", "Read not permitted for $uuid!")
}
else -> {
Log.e("BluetoothGattCallback", "Characteristic read failed for $uuid, error: $status")
}
}
}
}
}
The other callbacks work as expected - I am able to write, read rssi value, discover service etc.
Additionally, I know that the BLE device is working fine since BLE scanning apps form the PlayStore are able to read the value from it.
Where gattCallback is registered -
override fun onScanResult(callbackType: Int, result: ScanResult) {
if (isScanning) {
stopScan()
}
with(result.device) {
Log.i("ScanCallback", "Found BLE device! Name: ${name ?: "Unnamed"}, address: $address")
setGeneralStatusText("BLE Device Found - ${name ?: "Unnamed"}")
Log.i("ScanResultAdapter", "Connecting to $address")
setGeneralStatusText("Connecting to ${name ?: "Unnamed"} - $address")
connectGatt(baseContext, true, gattCallback, BluetoothDevice.TRANSPORT_LE)
}
}
Turns out the deprecated method needed to be called. More info here -