试图传递一个Byte数组，但得到* null对象引用*但为什么呢？

Question

Github链接到项目：https://github.com/vasugupta1/SecondDataKingApp

背景资讯

所以我正在尝试创建服务，一旦服务启动，它将读入一个充满传感器数据的文本文件，将其转换为字节数组并通过蓝牙发送。 我得到的错误是：

引起：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void com.example.vasu_linux.seconddatakingapp.BluetoothConnectionService $ ConnectedThread.write（byte []）' / EM>

我无法弄清楚为什么从myService类传递的字节数组不会进入BluetoothConnectionService类。

你们中的一个可爱的程序员可以建议一种方法，我可以将字节数组从服务类传递给bluetoothconnection类。我已经附加了githib项目链接，因此您可以更轻松地查看代码。

有两个主要类别是：

public class myService extends Service {
BluetoothConnectionService mBluetoothConnection;
@Nullable
@Override
public IBinder onBind(Intent intent) {
    return null;
}


@Override
public void onCreate() {
    super.onCreate();
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
   mBluetoothConnection = new BluetoothConnectionService(this);
   String news = "WOW";
   byte[] bytes = news.getBytes();
   mBluetoothConnection.write(bytes);


    return START_STICKY;
}

@Override
public void onDestroy() {
    super.onDestroy();
}

}

并且：

import android.app.ProgressDialog;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothServerSocket;
import android.bluetooth.BluetoothSocket;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Environment;
import android.util.Log;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.charset.Charset;
import java.util.UUID;


public class BluetoothConnectionService {
    private static final String TAG = "BluetoothConnectionServ";
    private static final String appName = "MYAPP";
    private static final UUID MY_UUID_INSECURE =
            UUID.fromString("8ce255c0-200a-11e0-ac64-0800200c9a66");
    private final BluetoothAdapter mBluetoothAdapter;
    Context mContext;
    private AcceptThread mInsecureAcceptThread;
    private ConnectThread mConnectThread;
    private BluetoothDevice mmDevice;
    private UUID deviceUUID;
    ProgressDialog mProgressDialog;
    private ConnectedThread mConnectedThread;







    public BluetoothConnectionService(Context context) {
        mContext = context;
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        start();





    }


    /**
     * This thread runs while listening for incoming connections. It behaves
     * like a server-side client. It runs until a connection is accepted
     * (or until cancelled).
     */
    private class AcceptThread extends Thread {

        // The local server socket
        private final BluetoothServerSocket mmServerSocket;

        public AcceptThread(){
            BluetoothServerSocket tmp = null;

            // Create a new listening server socket
            try{
                tmp = mBluetoothAdapter.listenUsingInsecureRfcommWithServiceRecord(appName, MY_UUID_INSECURE);

                Log.d(TAG, "AcceptThread: Setting up Server using: " + MY_UUID_INSECURE);
            }catch (IOException e){
                Log.e(TAG, "AcceptThread: IOException: " + e.getMessage() );
            }

            mmServerSocket = tmp;
        }

        public void run(){
            Log.d(TAG, "run: AcceptThread Running.");

            BluetoothSocket socket = null;

            try{
                // This is a blocking call and will only return on a
                // successful connection or an exception
                Log.d(TAG, "run: RFCOM server socket start.....");

                socket = mmServerSocket.accept();

                Log.d(TAG, "run: RFCOM server socket accepted connection.");

            }catch (IOException e){
                Log.e(TAG, "AcceptThread: IOException: " + e.getMessage() );
            }

            //talk about this is in the 3rd
            if(socket != null){
                connected(socket,mmDevice);
            }

            Log.i(TAG, "END mAcceptThread ");
        }

        public void cancel() {
            Log.d(TAG, "cancel: Canceling AcceptThread.");
            try {
                mmServerSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "cancel: Close of AcceptThread ServerSocket failed. " + e.getMessage() );
            }
        }

    }

    /**
     * This thread runs while attempting to make an outgoing connection
     * with a device. It runs straight through; the connection either
     * succeeds or fails.
     */
    private class ConnectThread extends Thread {
        private BluetoothSocket mmSocket;

        public ConnectThread(BluetoothDevice device, UUID uuid) {
            Log.d(TAG, "ConnectThread: started.");
            mmDevice = device;
            deviceUUID = uuid;
        }

        public void run(){
            BluetoothSocket tmp = null;
            Log.i(TAG, "RUN mConnectThread ");

            // Get a BluetoothSocket for a connection with the
            // given BluetoothDevice
            try {
                Log.d(TAG, "ConnectThread: Trying to create InsecureRfcommSocket using UUID: "
                        +MY_UUID_INSECURE );
                tmp = mmDevice.createRfcommSocketToServiceRecord(deviceUUID);
            } catch (IOException e) {
                Log.e(TAG, "ConnectThread: Could not create InsecureRfcommSocket " + e.getMessage());
            }

            mmSocket = tmp;

            // Always cancel discovery because it will slow down a connection
            mBluetoothAdapter.cancelDiscovery();

            // Make a connection to the BluetoothSocket

            try {
                // This is a blocking call and will only return on a
                // successful connection or an exception
                mmSocket.connect();

                Log.d(TAG, "run: ConnectThread connected.");
            } catch (IOException e) {
                // Close the socket
                try {
                    mmSocket.close();
                    Log.d(TAG, "run: Closed Socket.");
                } catch (IOException e1) {
                    Log.e(TAG, "mConnectThread: run: Unable to close connection in socket " + e1.getMessage());
                }
                Log.d(TAG, "run: ConnectThread: Could not connect to UUID: " + MY_UUID_INSECURE );
            }

            //will talk about this in the 3rd video
            connected(mmSocket,mmDevice);
        }
        public void cancel() {
            try {
                Log.d(TAG, "cancel: Closing Client Socket.");
                mmSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "cancel: close() of mmSocket in Connectthread failed. " + e.getMessage());
            }
        }
    }



    /**
     * Start the chat service. Specifically start AcceptThread to begin a
     * session in listening (server) mode. Called by the Activity onResume()
     */
    public synchronized void start() {
        Log.d(TAG, "start");

        // Cancel any thread attempting to make a connection
        if (mConnectThread != null) {
            mConnectThread.cancel();
            mConnectThread = null;
        }
        if (mInsecureAcceptThread == null) {
            mInsecureAcceptThread = new AcceptThread();
            mInsecureAcceptThread.start();
        }
    }

    /**
     AcceptThread starts and sits waiting for a connection.
     Then ConnectThread starts and attempts to make a connection with the other devices AcceptThread.
     **/

    public void startClient(BluetoothDevice device,UUID uuid){
        Log.d(TAG, "startClient: Started.");

        //initprogress dialog
        mProgressDialog = ProgressDialog.show(mContext,"Connecting Bluetooth"
                ,"Please Wait...",true);

        mConnectThread = new ConnectThread(device, uuid);
        mConnectThread.start();
    }

    /**
     Finally the ConnectedThread which is responsible for maintaining the BTConnection, Sending the data, and
     receiving incoming data through input/output streams respectively.
     **/
    public class ConnectedThread extends Thread {
        private final BluetoothSocket mmSocket;
        private final InputStream mmInStream;
        private final OutputStream mmOutStream;

        public ConnectedThread(BluetoothSocket socket) {
            Log.d(TAG, "ConnectedThread: Starting.");


           ///Change made here////////////
            mmSocket = socket;
            InputStream tmpIn = null;
            OutputStream tmpOut = null;
    /////////////////////////////////////////////////////

            //dismiss the progressdialog when connection is established
            try{
                mProgressDialog.dismiss();
            }catch (NullPointerException e){
                e.printStackTrace();
            }


            try {
                tmpIn = mmSocket.getInputStream();
                tmpOut = mmSocket.getOutputStream();
            } catch (IOException e) {
                e.printStackTrace();
            }

            mmInStream = tmpIn;
            mmOutStream = tmpOut;



            }

            public void send(){

                File file = new File(Environment.getExternalStoragePublicDirectory(
                        Environment.DIRECTORY_MOVIES), "Sensordata");
                byte[] bytesArray = new byte[(int) file.length()];
                FileInputStream fis;
                try {
                    fis = new FileInputStream(file);
                    fis.read(bytesArray); //read file into bytes[]
                    while(fis !=null) {
                        mmOutStream.write(bytesArray);
                        fis.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }


        public void run(){
            byte[] buffer = new byte[1024];  // buffer store for the stream

            int bytes; // bytes returned from read()

            // Keep listening to the InputStream until an exception occurs
            while (true) {
                // Read from the InputStream
                try {
                    bytes = mmInStream.read(buffer);
                    String incomingMessage = new String(buffer, 0, bytes);
                    Log.d(TAG, "InputStream: " + incomingMessage);
                } catch (IOException e) {
                    Log.e(TAG, "write: Error reading Input Stream. " + e.getMessage() );
                    break;
                }
            }
        }

        //Call this from the main activity to send data to the remote device
        public void write(byte[] bytes) {
            String text = new String(bytes, Charset.defaultCharset());
            Log.d(TAG, "write: Writing to outputstream: " + text);
            try {
                mmOutStream.write(bytes);
            } catch (IOException e) {
                Log.e(TAG, "write: Error writing to output stream. " + e.getMessage() );
            }
        }

        /* Call this from the main activity to shutdown the connection */
        public void cancel() {
            try {
                mmSocket.close();
            } catch (IOException e) { }
        }
    }

    private void connected(BluetoothSocket mmSocket, BluetoothDevice mmDevice) {
        Log.d(TAG, "connected: Starting.");

        // Start the thread to manage the connection and perform transmissions
        mConnectedThread = new ConnectedThread(mmSocket);
        mConnectedThread.start();
    }

    /**
     * Write to the ConnectedThread in an unsynchronized manner
     *
     * @param out The bytes to write
     * @see ConnectedThread#write(byte[])
     */
    public void write(byte[] out) {
        // Create temporary object
        ConnectedThread r;
        // Synchronize a copy of the ConnectedThread
        Log.d(TAG, "write: Write Called.");
        //perform the write
        mConnectedThread.write(out);
    }

}

Answer 1

在这里createOrReplaceTempView(df, "table") df2 <- sql("SELECT * FROM table") show(df2) # returns "<SQL> SELECT * FROM table" 之后，您很高兴继续：

IOException

因此 try { tmpIn = mmSocket.getInputStream(); tmpOut = mmSocket.getOutputStream(); } catch (IOException e) { e.printStackTrace(); } mmInStream = tmpIn; mmOutStream = tmpOut; } 和mmInStream可能未初始化。因此，mmOutStream方法中的mmOutStream.write(bytesArray);可能会在send()上调用。

检查控制台/系统，也许你甚至会看到例外。