IntentService 的蓝牙连接问题

Question

我需要通过蓝牙从我的 Android 应用程序传输一些数据（到 Arduino）。我不是 reading/receiving 从 Arduino 回来的任何东西。对于我的单线程需求，我选择了 IntentService。配对后，我的代码在我第一次连接和发送数据时工作正常。我在无误发送数据后断开连接。但是当我第二次尝试连接时，尝试 myBluetoothSocket.connect() :

时出现以下错误

read failed, socket might closed or timeout, read ret: -1

唯一的解决办法是关闭 Arduino 设备电源并重新连接（如果我强制停止应用程序并尝试重新连接，这无济于事）。

请注意，无论我连接和发送数据多少次，如果我生成 2 个线程（每个线程一个用于读取和写入）一切正常（从而证明 Arduino 方面没有任何问题，"holding back"旧连接）。

这是我的 Android 代码：

import android.app.IntentService;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.content.Context;
import android.os.Build;
import android.os.ParcelUuid;
import android.widget.Toast;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Method;
import java.util.UUID;

public class DataTransmissionService extends IntentService {

    private static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
    private static final String TAG = "DataTransmissionService";

    private BluetoothAdapter btAdapter = null;
    private BluetoothSocket btSocket = null;
    private OutputStream outStream = null;
    private BluetoothDevice device = null;

    public DataTransmissionService() {
        super("DataTransmissionService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        cleanup();
        if (intent != null){

            btAdapter = BluetoothAdapter.getDefaultAdapter();
            pairedDeviceAddress = "already_paired_device_mac_addr";

            try {
                log.d(TAG, pairedDeviceAddress);
                device = btAdapter.getRemoteDevice(pairedDeviceAddress);
                log.d(TAG, "Device bond state : " + device.getBondState());

            } catch (Exception e) {
                log.e(TAG, "Invalid address: " + e.getMessage());
                return;
            }

            try {
                btSocket = createBluetoothSocket(device);
            } catch (IOException e) {
                log.e(TAG, "Socket creation failed: " + e.getMessage());
                return;
            }

            try {

                if (!btSocket.isConnected()) {  
                    btSocket.connect();    
                    log.d(TAG, "Connected");
                } else {
                    log.d(TAG, "Already Connected");  //flow never reaches here for any use case
                }

            } catch (IOException e) {
                log.e(TAG, "btSocket.connect() failed : " + e.getMessage());
                return;
            }

            try {
                outStream = btSocket.getOutputStream();
            } catch (IOException e) {
                log.e(TAG, "Failed to get output stream:" + e.getMessage());
                return;
            }

            sendData("test");
           //cleanup();   called in onDestroy()

        }

    }

    @Override
    public void onDestroy(){
        cleanup();
        //notify ui
        super.onDestroy();
    }

    private void cleanup(){

        try {
            if (outStream != null) {
                outStream.close();
                outStream = null;
            }
        } catch (Exception e) {
            log.e(TAG, "Failed to close output stream : " + e.getMessage());
        }

        try {
            if (btSocket != null) {
                btSocket.close();
                btSocket = null;
            }
        }catch (Exception e) {
            log.e(TAG, "Failed to close connection : " + e.getMessage());
        }

    }

    private BluetoothSocket createBluetoothSocket(BluetoothDevice device) throws IOException {
        /*if(Build.VERSION.SDK_INT >= 10){
            try {
                final Method m = device.getClass().getMethod("createInsecureRfcommSocketToServiceRecord", new Class[] { UUID.class });
                return (BluetoothSocket) m.invoke(device, MY_UUID);
            } catch (Exception e) {
                log.e(TAG, "Could not create Insecure RFComm Connection",e);
            }
        }*/

        return  device.createRfcommSocketToServiceRecord(MY_UUID);
    }

    private void sendData(String message) {

        byte[] msgBuffer = message.getBytes();
        log.d(TAG, "Sending : " + message);
        try {
            outStream.write(msgBuffer);
        } catch (IOException e) {
            log.e(TAG, "failed to write " + message);
        }
    }
}

我已经在 Nexus 5 和 Samsung S5 设备上测试过（运行 5.1 和 5.0）。

Answer 1

当您第二次尝试连接时，您必须重新创建相应的套接字。

您还必须考虑到 Arduino 是一个缓慢的平台，在关闭连接和您能够再次打开它之间可能会有相当长的延迟。

Answer 2

onDestroy()方法仅在垃圾收集器运行时调用。您需要像以前一样从 onHandleIntent(Intent) 调用 cleanup() ，否则套接字将无限期保持打开状态。由于您将其打开，因此无法再次连接。

Android 的蓝牙堆栈似乎与应用程序生命周期无关：即使您强行停止应用程序，套接字仍将保持打开状态。在您当前的情况下，要关闭套接字，请在“设置”中禁用/启用蓝牙。

Answer 3

我不确定它为什么有效，但这种方法终于奏效了：

private BluetoothSocket createBluetoothSocket(BluetoothDevice bluetoothDevice) throws IOException {

        try {
            Method m = bluetoothDevice.getClass().getMethod(
                    "createRfcommSocket", new Class[] { int.class });
            btSocket = (BluetoothSocket) m.invoke(bluetoothDevice, 1);
        } catch (Exception e) {
            e.printStackTrace();
        }

        return btSocket;
    }

IntentService 的蓝牙连接问题

Bluetooth connection issues with IntentService

android

bluetooth