Android BLE Scan 永远找不到设备

Question

几天后，我尝试在我的 APP 中实现 BLE 连接。我知道我尝试连接的设备功能齐全，所以问题一定出在我的代码上。

我使用 BluetoothLeScanner.startScan() 方法。
但是永远不会调用回调方法。

   public void startScan() {
        if (bluetoothAdapter != null && bluetoothAdapter.isEnabled()) {
            isScanning = true;
            Handler mHandler = new Handler();
            mHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mainActivityHandler.setMSG("Scan stopped");
                    isScanning = false;
                    leScanner.stopScan(scanCallback);
                }
            }, SCAN_TIME);

            mainActivityHandler.setMSG("Start scan");

            try {

                leScanner.startScan(scanCallback);
            } catch (Exception e) {
                mainActivityHandler.catchError(e);
            }

        } else mainActivityHandler.catchError(new Exception("Bluetooth not activated"));
    }

我的 CallbackMethod(不知道我是否正确使用 gatt，但这是另一个问题):

    private ScanCallback scanCallback = new ScanCallback() {


    @Override
    public void onBatchScanResults(List<ScanResult> results) {
        mainActivityHandler.setMSG("Callback");
        isScanning = false;
        try {

            mainActivityHandler.setMSG("Connected to " + results.get(0).getDevice().getName());
            gatt = results.get(0).getDevice().connectGatt(mainActivity, true, bluetoothGattCallback);

            BluetoothGattDescriptor descriptor;
            for (int i = 0; i < charIDs.length; i++) {
                gatt.setCharacteristicNotification(gatt.getService(serviceID[0]).getCharacteristic(charIDs[i]), true);

                descriptor = gatt.getService(serviceID[0]).getCharacteristic(charIDs[0]).getDescriptor(charIDs[i]);
                descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
                gatt.writeDescriptor(descriptor);
            }
        } catch (Exception e) {
            mainActivityHandler.catchError(e);
        }

    }
};

Answer 1

问题

问题是您只是覆盖了 onBatchScanResults 方法，而不是 onScanResult 方法。 onBatchScanResults 只有在以下情况下才会被触发:

1. 您已使用 ScanSettings.Builder 将 ScanSettings 模式设置为 ScanSettings.SCAN_MODE_LOW_POWER(这是默认设置)。
2. 您已在 ScanSettings.Builder 中使用 setReportDelay(long reportDelayMillis) 将报告延迟时间设置为某个值 >0。

reportDelayMillis - Delay of report in milliseconds. Set to 0 to be notified of results immediately. Values > 0 causes the scan results to be queued up and delivered after the requested delay or when the internal buffers fill up.

例如:

public void startScan(BluetoothLeScanner scanner) {
    ScanFilter filter = new ScanFilter.Builder().setDeviceName(null).build();

    ArrayList<ScanFilter> filters = new ArrayList<ScanFilter>();
                    filters.add(filter);

    ScanSettings settings = new ScanSettings.Builder()
                                .setScanMode(ScanSettings.SCAN_MODE_LOW_POWER)
                                .setReportDelay(1l)
                                .build();

    Log.i(TAG,"The setting are "+settings.getReportDelayMillis());
    scanner.startScan(filters,settings,BLEScan);
}

解决方案

但是，您可能只想一次获得结果而不是一批结果。为此，您不必修改 ScanSettings，只需重写 ScanCallback 中的 onScanResult 方法即可。

private ScanCallback mScanCallback =
        new ScanCallback() {

    public void onScanResult(int callbackType, ScanResult result) {
        System.out.println(result.getDevice().getName())
        // Do whatever you want
    };

    ...
};

替代方案 - RxAndroidBle

无论如何，我强烈推荐使用库 RxAndroidBle .它维护得很好，它解决了许多开箱即用的 BLE 问题(扫描可能是 BLE 中不太复杂的部分)。

使用该库，扫描可以像这样完成:

Disposable scanSubscription = rxBleClient.scanBleDevices(


    new ScanSettings.Builder()
            // .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY) // change if needed
            // .setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES) // change if needed
            .build()
        // add filters if needed
)
    .subscribe(
        scanResult -> {
            // Process scan result here.
        },
        throwable -> {
            // Handle an error here.
        }
    );

// When done, just dispose.
scanSubscription.dispose();