Issue with Scanning Specific BLE Devices

Question

I am working on BLE and have to scan the BLE devices with specific udid.

Currently, All BLE supported devices comes as a scan result.

To avoid and scan only specific devices, what I have done is as below :

fun startScanDevices(interval: Long = Constants.DEFAULT_SCAN_TIME_OUT,
                     connectedDevices: HashMap<String, BLEDeviceModel>? = null,
                     scanWithId: String? = null, context: Activity? = null) {
    this.context = context
    if (scanWithId != null)
        this.scanWithId = scanWithId
    if (isBluetoothEnabled) {
        clearDeviceList(connectedDevices)
        val BLP_SERVICE_UUID = UUID.fromString(UUID_OF_DEVICE)
        val serviceUUIDs = arrayOf<UUID>(BLP_SERVICE_UUID)
        var filters: MutableList<ScanFilter?>? = null
        if (serviceUUIDs != null) {
            filters = ArrayList()
            for (serviceUUID in serviceUUIDs) {
                val filter: ScanFilter = ScanFilter.Builder()
                        .setServiceUuid(ParcelUuid(serviceUUID))
                        .build()
                filters!!.add(filter)
            }
        }
        val scanSettings: ScanSettings = ScanSettings.Builder()
                .setScanMode(ScanSettings.SCAN_MODE_LOW_POWER)
                .setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES)
                .setMatchMode(ScanSettings.MATCH_MODE_AGGRESSIVE)
                .setNumOfMatches(ScanSettings.MATCH_NUM_ONE_ADVERTISEMENT)
                .setReportDelay(1L)
                .build()
        mBluetoothAdapter?.bluetoothLeScanner?.startScan(filters,scanSettings,scanCallback)
        mScanning = true
        handler.postDelayed(stopScanningRunnable, interval)
    }
}

Now, here in above method, you can verify that I am passing filters and scanSettings as a arguments of startScan method.

But with these two arguments I am getting below error :

2021-05-06 11:16:24.295 14669-14669/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.dev, PID: 14669 java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 at java.util.ArrayList.get(ArrayList.java:437) at com.ble.BLEManager$scanCallback$1.onBatchScanResults(BLEManager.kt:153) at android.bluetooth.le.BluetoothLeScanner$BleScanCallbackWrapper$2.run(BluetoothLeScanner.java:627) at android.os.Handler.handleCallback(Handler.java:938) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:246) at android.app.ActivityThread.main(ActivityThread.java:8506) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)

This is working fine with single arguments in startScan() as below - not getting this error :

mBluetoothAdapter?.bluetoothLeScanner?.startScan(scanCallback)

So, Error is in below method :

override fun onBatchScanResults(results: List<ScanResult>) {
            results[0].device
            super.onBatchScanResults(results)
        }

EDIT

Removed this unnecessary Method named : onBatchScanResults since I am using onScanResult.

Now, Error is not coming but, not able to scan any devices with the filter and scanSettings.

What might be the issue? Please guide. Thanks.

You probably get this `IndexOutOfBoundsException` because you try to access the element with index 0 (`results[0].device`) without checking a priori whether there is any element (with index 0) in the parameter `results`. — Chilippso, May 07 '21 at 18:58
That's fine. But I have commented the onBatchScanResults() method. Now the issue is I am not getting any list data in onScanResult. — Jaimin Modi, May 10 '21 at 12:46

score 0 · Answer 1 · answered May 14 '21 at 08:23

step 1) Add filter like this :

String[] filterNames = intent.getStringArrayExtra(FILTER_NAME_LIST);

String[] filterMacs = intent.getStringArrayExtra(FILTER_MAC_LIST);

String[] ignoreMacs = intent.getStringArrayExtra(IGNORE_MAC_LIST);

mFilter = new ScanServiceFilter.Builder() .filterNames(filterNames) .filterMacs(filterMacs) .ignoreMacs(ignoreMacs) .build();

step 2: call the scanLeDevice()

scanLeDevice(true);

step 3: scanLeDevice create setting

                 ScanSettings settings = new ScanSettings.Builder()
                .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
                .setCallbackType(CALLBACK_TYPE_ALL_MATCHES)
                .setMatchMode(MATCH_MODE_AGGRESSIVE)
                .setNumOfMatches(MATCH_NUM_FEW_ADVERTISEMENT)
                .setReportDelay(0)
                .build();

        // We only want to scan for devices advertising our custom service
        ScanFilter scanFilter = new ScanFilter.Builder()
                .setServiceUuid(new ParcelUuid(UUIDConstants.RX_SERVICE_UUID)).build();
        if (mBluetoothLeScanner != null && mBluetoothAdapter.getState() == BluetoothAdapter.STATE_ON) {
            mBluetoothLeScanner.startScan(Collections.singletonList(scanFilter), settings, mScanCallback);
            broadcastAction(new ScanBleActionEvent(ScanBleActionEvent.Actions.SCAN_STARTED));
        } else {
            bluetoothDeviceStopped();
        }

step 4: on ScanCallback check

    if (mFilter.passesFilter(scanDevice)) {
                filteredResults.add(scanDevice);
                broadcastAction(new ScanBleActionEvent(ScanBleActionEvent.Actions.SCANNED_DEVICE, scanDevice));
            }

Okay will try this later on and let you know that this is working or not.. — Jaimin Modi, May 18 '21 at 06:43

Issue with Scanning Specific BLE Devices

1 Answers1