无法连接外部蓝牙条码扫描器

Question

我正在尝试将我的应用程序与外部蓝牙条码扫描器（YHD-3100）连接，但当我尝试从BluetoothSocket调用.connect（）时，我一直收到java.io.IOException: read failed, socket might closed or timeout, read ret: -1。

当我连接无线打印机（能够打印出来没有问题）时，此代码工作正常但是条形码扫描仪失败了。这可能是什么原因？

这是我的代码：

public class BluetoothConnect implements Runnable {

    // Code eliminated 

    public BluetoothConnect(Context context, int device) {
        // Code eliminated 
    }

    public String retrieveBarcode() {
        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if(bluetoothAdapter.isEnabled()) {
            Log.d(TAG, "Bluetooth enabled");
            getBluetoothList(device, true);
        } else {
            Log.d(TAG, "Bluetooth disabled");
            alertDialog(TITLE_BLUETOOTH_OFF, MESSAGE_BLUETOOTH_OFF);
        }

        return barcode;
    }

    private void getBarcode() {
        Log.d(TAG, "Attempt to retrieve barcode");
        Thread thread = new Thread() {
            public void run() {
                try {
                    InputStream inputStream = bluetoothSocket.getInputStream();
                    BufferedReader r = new BufferedReader(new InputStreamReader(inputStream));
                    StringBuilder sb = new StringBuilder();
                    String line;
                    while ((line = r.readLine()) != null) {
                        sb.append(line).append('\n');
                    }
                    barcode = sb.toString();
                } catch (Exception e) {
                    Log.e(TAG, "Unable to retrieve barcode", e);
                }
            }
        };

        thread.start();
    }

    private void getBluetoothList(int device, boolean isExecute) {
        Log.d(TAG, "Retrieve list of bluetooth");
        Set<BluetoothDevice> pairedSet = bluetoothAdapter.getBondedDevices();
        int size = pairedSet.size();

        if(size > 0) {
            ArrayList<String> bluetoothArray = new ArrayList<>();
            for(BluetoothDevice bluetoothDevice : pairedSet) {
                // Only display in list for wireless printer devices
                if(bluetoothDevice != null && bluetoothDevice.getBluetoothClass().getDeviceClass() == device) {
                    pairedDevices.add(bluetoothDevice);
                    bluetoothArray.add(bluetoothDevice.getName());
                    Log.d(TAG, "Device: " + bluetoothDevice.getName());
                }
            }

            bluetoothList = bluetoothArray.toArray(new CharSequence[bluetoothArray.size()]);
            alertBluetoothListDialog();
        } 
    }

    private void alertBluetoothListDialog() {
        Log.d(TAG, "Open dialog for bluetooth list");
        AlertDialog.Builder builder = new AlertDialog.Builder(context);
        builder.setIcon(R.drawable.ic_attach_money_black_24dp);
        if(device == TYPE_PRINTER) {
            builder.setTitle(TITLE_BLUETOOTH_PRINTER);
        } else if(device == TYPE_BARCODE_SCANNER) {
            builder.setTitle(TITLE_BLUETOOTH_SCANNER);
        }
        builder.setItems(bluetoothList, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                bluetoothDevice = pairedDevices.get(which);
                setBluetoothItems();
                dialog.dismiss();
            }
        });

        builder.show();
    }

    private void setBluetoothItems() {
        bluetoothAdapter.cancelDiscovery();
        deviceMacAddress = bluetoothDevice.getAddress();

        // Retrieve device's first UUID
        ParcelUuid[] list = bluetoothDevice.getUuids();
        if(list[0] != null) {
            deviceUUID = list[0].toString();
        }

        connectAppToDevice();
    }

    private void connectAppToDevice() {
        Log.d(TAG, "Attempt to connect app to device");
        bluetoothDevice = bluetoothAdapter.getRemoteDevice(deviceMacAddress);
        bluetoothConnectProgressDialog = ProgressDialog.show(context,
                "Connecting...", bluetoothDevice.getName(), true, false);
        Thread bluetoothConnectThread = new Thread(this);
        bluetoothConnectThread.start();
    }

    private void alertDialog(String title, String message) {
        AlertDialog.Builder builder = new AlertDialog.Builder(context);
        builder.setIcon(R.drawable.ic_warning_24dp);
        builder.setTitle(title);
        builder.setMessage(message);

        builder.setNegativeButton(MESSAGE_OK, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });

        builder.show();
    }

    public void run() {
        try {
            UUID appUUID = UUID.fromString(deviceUUID);
            bluetoothSocket = bluetoothDevice.createRfcommSocketToServiceRecord(appUUID);
            bluetoothAdapter.cancelDiscovery();
            bluetoothSocket.connect();
            handler.sendEmptyMessage(0);
        } catch (IOException eConnectException) {
            closeSocket(bluetoothSocket, true);
        }
    }

    private void closeSocket(BluetoothSocket openSocket, boolean isError) {
        try {
            openSocket.close();
            bluetoothConnectProgressDialog.dismiss();
        } catch (IOException ex) {
            Log.d(TAG, "Could not close socket");
        }
    }

    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            bluetoothConnectProgressDialog.dismiss();
            getBarcode();
            closeSocket(bluetoothSocket, false);
        }
    };
}