要查找 BLE 设备,您可以使用 startScan()
方法。此方法接受 ScanCallback
作为参数。您必须实现此回调,因为扫描结果是通过它返回的。由于扫描会消耗大量电池电量,您应遵守以下准则
- 找到所需设备后,立即停止扫描。
- 切勿循环扫描,并始终为扫描设置时间限制。之前可用的设备可能已移出范围,继续扫描会消耗电池电量。
在以下示例中,BLE 应用提供了一个 Activity (DeviceScanActivity
) 用于扫描可用的低功耗蓝牙设备并将其显示在列表中供用户查看。以下代码段展示了如何开始和停止扫描
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); } }
要仅扫描特定类型的外围设备,您可以改为调用 startScan(List<ScanFilter>, ScanSettings, ScanCallback)
,提供一个 ScanFilter
对象列表来限制扫描寻找的设备,以及一个 ScanSettings
对象来指定扫描参数。
以下代码示例是 ScanCallback
的实现,该接口用于传递 BLE 扫描结果。找到结果时,它们会被添加到 DeviceScanActivity
中的列表适配器中,以显示给用户。
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(); } };