Android BLE 扫描永远找不到设备

Question

几天以来，我尝试在我的应用程序中实现 BLE 连接。我知道我尝试连接的设备功能齐全，因此问题一定是我的代码。

我用的是BluetoothLeScanner.startScan()方法。
但回调方法永远不会被调用。

   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

问题是你只是重写了onBatchScanResults方法而不是onScanResult方法。onBatchScanResults仅在以下情况下才会被触发：

1. 您已使用 .bat 将ScanSettings模式设置为ScanSettings.SCAN_MODE_LOW_POWER（这是默认设置）ScanSettings.Builder。
2. 您已setReportDelay(long reportDelayMillis)在ScanSettings.Builder.

reportDelayMillis - 报告延迟（以毫秒为单位）。设置为 0 可立即通知结果。值 > 0 会导致扫描结果排队并在请求的延迟后或内部缓冲区填满时传送。

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一次结果，而不是一批结果。要实现这一点，您不必修改 ScanSettings，只需重写onScanResult您的方法ScanCallback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

不管怎样，我强烈推荐使用RxAndroidBle库。它维护得很好，并且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，可以像这样完成扫描：

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();