Kotlin I have a problem with BLE ScanCallback

Question

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
    private fun discover(){
        val mBluetoothLeScanner: BluetoothLeScanner =BluetoothAdapter.getDefaultAdapter().bluetoothLeScanner
        val mHandler: Handler = Handler()
        val scanCallback = object:ScanCallback() {
            override fun onScanResult(callbackType: Int, result: ScanResult?) {
                Log.d(TAG, "onscanresult...")
                super.onScanResult(callbackType, result)

                if (result == null || result.getDevice() == null || TextUtils.isEmpty(result.getDevice().getName())
                ) return

                val builder = StringBuilder(result.getDevice().getName())
                builder.append("\n").append(
                    result.getScanRecord()
                        ?.getServiceData(result.getScanRecord()!!.getServiceUuids().get(0)),
                    Charset.forName("UTF-8")
                )
                //Observed result
                Log.d(TAG, builder.toString())
            }

            override fun onBatchScanResults(results:List<ScanResult>?){
                Log.d(TAG, "Scanning...")
                super.onBatchScanResults(results)
            }

            override fun onScanFailed(errorCode: Int) {
                Log.d(TAG, "Discovery onScanFailed: $errorCode")
                super.onScanFailed(errorCode)
            }
        }

        val filters: ArrayList<ScanFilter> = ArrayList<ScanFilter>()
        val uuid = UUID.randomUUID()
        val filter: ScanFilter = ScanFilter.Builder().setServiceUuid(ParcelUuid(UUID.fromString("uuid"))).build()
        filters.add(filter)
        val settings: ScanSettings = ScanSettings.Builder().setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY).build()
        mBluetoothLeScanner?.startScan(filters, settings, scanCallback)
        Log.d(TAG, "StartScan...")
        mHandler.postDelayed(object : Runnable {
            override fun run() {
                mBluetoothLeScanner?.stopScan(scanCallback)
            }
        }, 10000)
        finish()
    }

On the code above, I have implemented BLE Scanning to receive a string. However, it seems like scanCallback has problem, but I am not sure what is it. On the Logcat, it shows "Startscan...", but it doesn't show "onscanresult...", so I assume the problem is on scanCallback. What could be the reason?? This code was written based on https://code.tutsplus.com/tutorials/how-to-advertise-android-as-a-bluetooth-le-peripheral--cms-25426 , but as the example is in Java, I have implemented on Kotlin by myself.

Answer 1

Can you try sending null to startScan like this

mBluetoothLeScanner?.startScan(null, settings, scanCallback)

Refer to ScanFilter doc it says

Criteria for filtering result from Bluetooth LE scans. A ScanFilter allows clients to restrict scan results to only those that are of interest to them.

So I think when you are setting the filter it is filtering the results from coming to onScanResult based on your criteria. Try removing it and if it works than the problem lies in your filtering criteria and you should try to debug that. Maybe the service id that the device you are looking for is sending is wrong.