Find BLE devices

To find BLE devices, you use the startScan() method. This method takes a ScanCallback as a parameter. You must implement this callback, because that is how scan results are returned. Because scanning is battery-intensive, you should observe the following guidelines:

  • As soon as you find the desired device, stop scanning.
  • Never scan on a loop, and always set a time limit on your scan. A device that was previously available may have moved out of range, and continuing to scan drains the battery.

In the following example, the BLE app provides an activity (DeviceScanActivity) to scan for available Bluetooth LE devices and display them in a list to the user. The following snippet shows how to start and stop a scan:

Kotlin

private val bluetoothLeScanner = bluetoothAdapter.bluetoothLeScanner
private var scanning = false
private val handler = Handler()

// Stops scanning after 10 seconds.
private val SCAN_PERIOD: Long = 10000

private fun scanLeDevice() {
    if (!scanning) { // Stops scanning after a pre-defined scan period.
        handler.postDelayed({
            scanning = false
            bluetoothLeScanner.stopScan(leScanCallback)
        }, SCAN_PERIOD)
        scanning = true
        bluetoothLeScanner.startScan(leScanCallback)
    } else {
        scanning = false
        bluetoothLeScanner.stopScan(leScanCallback)
    }
}

Java

private BluetoothLeScanner bluetoothLeScanner = bluetoothAdapter.getBluetoothLeScanner();
private boolean scanning;
private Handler handler = new Handler();

// Stops scanning after 10 seconds.
private static final long SCAN_PERIOD = 10000;

private void scanLeDevice() {
    if (!scanning) {
        // Stops scanning after a predefined scan period.
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                scanning = false;
                bluetoothLeScanner.stopScan(leScanCallback);
            }
        }, SCAN_PERIOD);

        scanning = true;
        bluetoothLeScanner.startScan(leScanCallback);
    } else {
        scanning = false;
        bluetoothLeScanner.stopScan(leScanCallback);
    }
}

To scan for only specific types of peripherals, you can instead call startScan(List<ScanFilter>, ScanSettings, ScanCallback), providing a list of ScanFilter objects that restrict the devices that the scan looks for and a ScanSettings object that specifies parameters about the scan.

The following code sample is an implementation of ScanCallback, which is the interface used to deliver BLE scan results. When results are found, they are added to a list adapter in the DeviceScanActivity to display to the user.

Kotlin

private val leDeviceListAdapter = LeDeviceListAdapter()
// Device scan callback.
private val leScanCallback: ScanCallback = object : ScanCallback() {
    override fun onScanResult(callbackType: Int, result: ScanResult) {
        super.onScanResult(callbackType, result)
        leDeviceListAdapter.addDevice(result.device)
        leDeviceListAdapter.notifyDataSetChanged()
    }
}

Java

private LeDeviceListAdapter leDeviceListAdapter = new LeDeviceListAdapter();

// Device scan callback.
private ScanCallback leScanCallback =
        new ScanCallback() {
            @Override
            public void onScanResult(int callbackType, ScanResult result) {
                super.onScanResult(callbackType, result);
                leDeviceListAdapter.addDevice(result.getDevice());
                leDeviceListAdapter.notifyDataSetChanged();
            }
        };