Java Android应用程序在试图通过蓝牙写入数据时不断抛出空指针异常

我目前正在进行一个项目，我正在构建一个应用程序，使用蓝牙向我的Arduino Uno发送命令，除了实际发送数据外，其他一切都正常工作

每当我尝试发送数据时，它都会抛出一个空指针异常，而我所知道的这些异常是在未初始化或找不到某些内容时抛出的（如果我错了，请纠正我）。因此，我认为问题在于我的connectedThread没有正确初始化，但我不知道在哪里执行此操作以及执行什么操作

还有一些其他的语音到文本的代码，所以忽略它

我真的很感激任何帮助或建议

非常感谢你

My Main_Activity.java：

package marggraffd.developer.com.robot;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.ActivityNotFoundException;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.speech.RecognizerIntent;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Locale;
import java.util.Set;
import java.util.UUID;


public class MainActivity extends AppCompatActivity implements          View.OnClickListener, AdapterView.OnItemClickListener {

public static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
private static final int SUCCESS_CONNECT = 0;
private static final int MESSAGE_READ = 1;
private static final String TAG = null;
Toolbar toolbar;
FloatingActionButton fab;
Button forward, reverse, left, right, stop;

private final int REQ_CODE_SPEECH_INPUT = 100;
TextView speech;
String text;
ArrayAdapter<String> listAdapter;
ListView listView;
ArrayList<String> pairedDevices;
ArrayList<BluetoothDevice> devices;
private BluetoothAdapter btAdapter;
Set<BluetoothDevice> devicesArray;
IntentFilter filter;
BroadcastReceiver receiver;


ConnectedThread connectedThread = null;


Handler mHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        switch (msg.what) {
            case SUCCESS_CONNECT:
                ConnectedThread connectedThread = new ConnectedThread((BluetoothSocket) msg.obj);
                Toast.makeText(getApplicationContext(), getResources().getString(R.string.bluetooth_success), Toast.LENGTH_LONG).show();
                String s = "Successfully Connected";
                connectedThread.write(s);
                break;
            case MESSAGE_READ:
                byte[] readBuff = (byte[]) msg.obj;
                String string = new String(readBuff);
                Toast.makeText(getApplicationContext(), string, Toast.LENGTH_LONG).show();
                break;
        }
    }
};


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    init();


    btAdapter = BluetoothAdapter.getDefaultAdapter();
    if (btAdapter == null) {
        Toast.makeText(getApplicationContext(), getResources().getString(R.string.error2), Toast.LENGTH_LONG).show();

    } else {
        if (!btAdapter.isEnabled()) {
            turnOnBT();
        }

        getPairedDevices();
        startDiscovery();
    }


}

private void startDiscovery() {
    btAdapter.cancelDiscovery();
    btAdapter.startDiscovery();

}

private void turnOnBT() {
    Intent intent = new Intent((BluetoothAdapter.ACTION_REQUEST_ENABLE));
    startActivityForResult(intent, 1);
}

private void getPairedDevices() {
    devicesArray = btAdapter.getBondedDevices();
    if (devicesArray.size() > 0) {
        for (BluetoothDevice device : devicesArray) {
            pairedDevices.add(device.getName());

        }
    }

}


private void init() {

    fab = (FloatingActionButton) findViewById(R.id.fab);
    forward = (Button) findViewById(R.id.bForward);
    reverse = (Button) findViewById(R.id.bReverse);
    left = (Button) findViewById(R.id.bLeft);
    right = (Button) findViewById(R.id.bRight);
    stop = (Button) findViewById(R.id.bStop);
    speech = (TextView) findViewById(R.id.textView3);

    listView = (ListView) findViewById(R.id.listView);
    listView.setOnItemClickListener(this);
    listAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, 0);
    listView.setAdapter(listAdapter);
    pairedDevices = new ArrayList<String>();
    filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);

    devices = new ArrayList<BluetoothDevice>();

    receiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();

            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                devices.add(device);
                String s = "";
                for (int a = 0; a < pairedDevices.size(); a++) {
                    if (device.getName().equals(pairedDevices.get(a))) {

                        s = "(Paired)";
                        break;
                    }

                }
                listAdapter.add(device.getName() + " " + s + " " + "\n" + device.getAddress());
            } else if (BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)) {

            } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {


            } else if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
                if (btAdapter.getState() == btAdapter.STATE_OFF) {
                    turnOnBT();
                }
            }

        }
    };

    registerReceiver(receiver, filter);
    filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
    registerReceiver(receiver, filter);
    filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
    registerReceiver(receiver, filter);
    filter = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
    registerReceiver(receiver, filter);


    fab.setOnClickListener(this);
    stop.setOnClickListener(this);

    buttons();


}


@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.bStop:
            connectedThread.write("e");
            break;
        case R.id.fab:
            speech();
            break;

    }
}

private void speech() {
    Intent i = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
    i.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL, RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
    i.putExtra(RecognizerIntent.EXTRA_LANGUAGE, Locale.getDefault());
    i.putExtra(RecognizerIntent.EXTRA_PROMPT, getString(R.string.speech_prompt));

    try {
        startActivityForResult(i, REQ_CODE_SPEECH_INPUT);
    } catch (ActivityNotFoundException a) {
        Toast.makeText(getApplicationContext(), getString(R.string.error), Toast.LENGTH_LONG).show();
        startActivityForResult(i, REQ_CODE_SPEECH_INPUT);


    }
}


@Override
protected void onPause() {
    super.onPause();
    unregisterReceiver(receiver);

}


@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == REQ_CODE_SPEECH_INPUT && resultCode == RESULT_OK) {

        ArrayList<String> result = data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS);
        speech.setText(result.get(0));

        text = speech.getText().toString();


        if (text == getString(R.string.forward)) {
            Toast.makeText(getApplicationContext(), "Forward", Toast.LENGTH_LONG).show();
        } else if (text == getString(R.string.reverse)) {
            Toast.makeText(getApplicationContext(), "Reverse", Toast.LENGTH_LONG).show();
        } else if (text == getString(R.string.left)) {
            Toast.makeText(getApplicationContext(), "Left", Toast.LENGTH_LONG).show();
        } else if (text == getString(R.string.right)) {
            Toast.makeText(getApplicationContext(), "Right", Toast.LENGTH_LONG).show();
        } else if (text == getString(R.string.stop)) {
            Toast.makeText(getApplicationContext(), "Stop", Toast.LENGTH_LONG).show();
        }

    }
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}


@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

    if (btAdapter.isDiscovering()) {
        btAdapter.cancelDiscovery();
    }
    if (listAdapter.getItem(position).contains("(Paired)")) {

        BluetoothDevice selectedDevices = devices.get(position);
        ConnectThread connect = new ConnectThread(selectedDevices);
        connect.start();
    } else {
        Toast.makeText(getApplicationContext(), getResources().getString(R.string.bluetooth_unpaired), Toast.LENGTH_LONG).show();
    }

}

private class ConnectThread extends Thread {
    private final BluetoothSocket mmSocket;
    private final BluetoothDevice mmDevice;

    public ConnectThread(BluetoothDevice device) {

        BluetoothSocket tmp = null;
        mmDevice = device;


        try {

            tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) {
        }
        mmSocket = tmp;
    }

    public void run() {

        btAdapter.cancelDiscovery();

        try {

            mmSocket.connect();
        } catch (IOException connectException) {

            try {
                mmSocket.close();
            } catch (IOException closeException) {
            }
            return;
        }


        mHandler.obtainMessage(SUCCESS_CONNECT, mmSocket).sendToTarget();
    }


    public void cancel() {
        try {
            mmSocket.close();
        } catch (IOException e) {
        }
    }
}

private class ConnectedThread extends Thread {
    private final BluetoothSocket mmSocket;
    private final InputStream mmInStream;
    private final OutputStream mmOutStream;

    public ConnectedThread(BluetoothSocket socket) {

        mmSocket = socket;
        InputStream tmpIn = null;
        OutputStream tmpOut = null;

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

        mmInStream = tmpIn;
        mmOutStream = tmpOut;
    }


    public void run() {
        byte[] buffer = new byte[9600];
        int bytes;

        while (true) {
            try {
                buffer = new byte[9600];

                bytes = mmInStream.read(buffer);

                mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
                        .sendToTarget();

            } catch (IOException e) {
                break;
            }
        }
    }

    public void write(String message) {
        byte[] msgBuffer = message.getBytes();

        try {
            mmOutStream.write(msgBuffer);
        } catch (IOException e) {
            e.printStackTrace();
        }


    }


    public void cancel() {
        try {
            mmSocket.close();
        } catch (IOException e) {
        }
    }

}

private void buttons() {


    forward.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    try {
                        connectedThread.write("e");
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    Toast.makeText(getApplicationContext(), "Forward", Toast.LENGTH_SHORT).show();
                    break;
                case MotionEvent.ACTION_UP:

                    connectedThread.write("e");
                    Toast.makeText(getApplicationContext(), "Stop", Toast.LENGTH_SHORT).show();
                    break;
            }
            return false;
        }
    });
    reverse.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    connectedThread.write("d");
                    Toast.makeText(getApplicationContext(), "Reverse", Toast.LENGTH_SHORT).show();
                    break;
                case MotionEvent.ACTION_UP:
                    connectedThread.write("e");
                    Toast.makeText(getApplicationContext(), "Stop", Toast.LENGTH_SHORT).show();
                    break;
            }
            return false;
        }
    });
    left.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    connectedThread.write("b");
                    Toast.makeText(getApplicationContext(), "Left", Toast.LENGTH_SHORT).show();
                    break;
                case MotionEvent.ACTION_UP:
                    connectedThread.write("e");
                    Toast.makeText(getApplicationContext(), "Stop", Toast.LENGTH_SHORT).show();
                    break;
            }
            return false;
        }
    });
    right.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    connectedThread.write("c");
                    Toast.makeText(getApplicationContext(), "Right", Toast.LENGTH_SHORT).show();
                    break;
                case MotionEvent.ACTION_UP:
                    connectedThread.write("e");
                    Toast.makeText(getApplicationContext(), "Stop", Toast.LENGTH_SHORT).show();
                    break;
            }
            return false;
        }
    });
}

---

根据您的

LogCat

错误消息：

java.lang.NullPointerException
10-01 18:32:00.481 21197-21197/marggraffd.developer.com.robot W/System.err:      at marggraffd.developer.com.robot.MainActivity$3.onTouch(MainActivity.java:429)

错误在这一行：

  connectedThread.write("e");

变量

connectedThread

的值仍为

null

，请检查代码以正确初始化

connectedThread

...
...
...
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    try {
                        connectedThread.write("e"); //*** connectedThread is NULL
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    Toast.makeText(getApplicationContext(), "Forward", Toast.LENGTH_SHORT).show();
...
...

---

定义为类字段：

ConnectedThread connectedThread = null;

ConnectedThread connectedThread = new ConnectedThread((BluetoothSocket) msg.obj);

然后您有一个

处理程序

，它处理一个

连接成功

，并将一个新的

连接线程

分配给一个局部变量，not类字段：

ConnectedThread connectedThread = null;

ConnectedThread connectedThread = new ConnectedThread((BluetoothSocket) msg.obj);

我在你的代码中没有看到的是你实际上在哪里创建了一个

ConnectedThread

并启动它，更不用说你在哪里给你的类字段分配了一个，你经常用它来写

东西

因此，在您的
onTouch
方法中抛出了一个
NullPointerException
，因为没有
connectedThread
，非常感谢您的帮助。我已经解决了这个问题。我刚刚在ConnectThread类中run（）的末尾初始化了线程，现在它工作得很好

如果其他任何人面临同样的问题，这就是必须解决的问题：

private class ConnectThread extends Thread {
    private final BluetoothSocket mmSocket;
    private final BluetoothDevice mmDevice;

    public ConnectThread(BluetoothDevice device) {

        BluetoothSocket tmp = null;
        mmDevice = device;


        try {

            tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) {
        }
        mmSocket = tmp;
    }

    public void run() {

        btAdapter.cancelDiscovery();

        try {

            mmSocket.connect();
        } catch (IOException connectException) {

            try {
                mmSocket.close();
            } catch (IOException closeException) {
            }
            return;
        }


        mHandler.obtainMessage(SUCCESS_CONNECT, mmSocket).sendToTarget();

        connectedThread = new ConnectedThread(mmSocket);
        connectedThread.start();

    }


    public void cancel() {
        try {
            mmSocket.close();
        } catch (IOException e) {
        }
    }

}

您好@Dietmar，MainActivity.java第429行有什么内容？可能是重复的@Elanasys感谢您的帮助。很抱歉要问，如果可以的话，你能告诉我如何初始化它吗？谢谢你的帮助@Sascha Kolberg。我一直试图在不同的地方启动线程，但每次都会出现更多错误。你能告诉我在哪里做这件事吗？如果可以的话，怎么做？