如要尋找 BLE 裝置,請使用 startScan()
方法。這個方法會使用 ScanCallback
做為參數。您必須實作這個回呼,因為這才會傳回掃描結果。由於掃描非常耗電,因此您應觀察下列準則:
- 找到所需裝置後,請立即停止掃描。
- 請勿在執行循環掃描時,一律設定掃描時間限制。之前可以使用的裝置可能已移出範圍,以便繼續掃描而減少電池的電量。
在以下範例中,BLE 應用程式提供一項活動 (DeviceScanActivity
) 來掃描可用的藍牙 LE 裝置,並在清單中向使用者顯示。下列程式碼片段說明如何開始及停止掃描作業:
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); } }
如果只要掃描特定類型的周邊裝置,可以改為呼叫 startScan(List<ScanFilter>, ScanSettings, ScanCallback)
,提供 ScanFilter
物件清單來限制掃描作業尋找的裝置,並提供 ScanSettings
物件,用於指定掃描作業的參數。
以下程式碼範例是 ScanCallback
的實作,這個介面可用於提供 BLE 掃描結果。找到結果後,系統會將結果新增至 DeviceScanActivity
的清單轉接程式,以便向使用者顯示。
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(); } };