Java 从蓝牙接收数据时获取NullPointerException

我必须从不是android设备的蓝牙设备到android手机获取数据。 作为安卓手机的接收器，我制作了一个应用程序来接收来自蓝牙设备的数据。 我在这里按照一篇帖子的答案做了一个教程

但是我得到了NullPointerException。 有人能告诉我为什么我会得到这个例外吗 有人能告诉我如何在代码中解决这个异常吗

我的代码是：

    package Android.Arduino.Bluetooth;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.TextView;
import android.widget.EditText;  
import android.widget.Button;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Set;
import java.util.UUID;

public class MainActivity extends Activity
{
TextView myLabel;
EditText myTextbox;
BluetoothAdapter mBluetoothAdapter;
BluetoothSocket mmSocket;
BluetoothDevice mmDevice;
OutputStream mmOutputStream;
InputStream mmInputStream;
Thread workerThread;
byte[] readBuffer;
int readBufferPosition;
int counter;
volatile boolean stopWorker;

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button openButton = (Button)findViewById(R.id.open);
    Button sendButton = (Button)findViewById(R.id.send);
    Button closeButton = (Button)findViewById(R.id.close);
    myLabel = (TextView)findViewById(R.id.label);
    myTextbox = (EditText)findViewById(R.id.entry);

     //Open Button
        openButton.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                try 
                {
                    findBT();
                    openBT();
                }
                catch (IOException ex) { }
            }
        });

        //Send Button
        sendButton.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                try 
                {
                    sendData();
                }
                catch (IOException ex) { }
            }
        });

        //Close button
        closeButton.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                try 
                {
                    closeBT();
                }
                catch (IOException ex) { }
            }
        });
    }

    void findBT()
    {
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if(mBluetoothAdapter == null)
        {
            myLabel.setText("No bluetooth adapter available");
        }

        if(!mBluetoothAdapter.isEnabled())
        {
            Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBluetooth, 0);
        }

        Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
        if(pairedDevices.size() > 0)
        {
            for(BluetoothDevice device : pairedDevices)
            {
                if(device.getName().equals("MattsBlueTooth")) 
                {
                    mmDevice = device;
                    break;
                }
            }
        }
        myLabel.setText("Bluetooth Device Found");
    }

    void openBT() throws IOException
    {
        UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"); //Standard SerialPortService ID
        mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);        
        mmSocket.connect();
        mmOutputStream = mmSocket.getOutputStream();
        mmInputStream = mmSocket.getInputStream();

        beginListenForData();

        myLabel.setText("Bluetooth Opened");
    }

    void beginListenForData()
    {
        final Handler handler = new Handler(); 
        final byte delimiter = 10; //This is the ASCII code for a newline character

        stopWorker = false;
        readBufferPosition = 0;
        readBuffer = new byte[1024];
        workerThread = new Thread(new Runnable()
        {
            public void run()
            {                
               while(!Thread.currentThread().isInterrupted() && !stopWorker)
               {
                    try 
                    {
                        int bytesAvailable = mmInputStream.available();                        
                        if(bytesAvailable > 0)
                        {
                            byte[] packetBytes = new byte[bytesAvailable];
                            mmInputStream.read(packetBytes);
                            for(int i=0;i<bytesAvailable;i++)
                            {
                                byte b = packetBytes[i];
                                if(b == delimiter)
                                {
         byte[] encodedBytes = new byte[readBufferPosition];
         System.arraycopy(readBuffer, 0, encodedBytes, 0, encodedBytes.length);
         final String data = new String(encodedBytes, "US-ASCII");
         readBufferPosition = 0;

                                    handler.post(new Runnable()
                                    {
                                        public void run()
                                        {
                                            myLabel.setText(data);
                                        }
                                    });
                                }
                                else
                                {
                                    readBuffer[readBufferPosition++] = b;
                                }
                            }
                        }
                    } 
                    catch (IOException ex) 
                    {
                        stopWorker = true;
                    }
               }
            }
        });

        workerThread.start();
    }

    void sendData() throws IOException
    {
        String msg = myTextbox.getText().toString();
        msg += "\n";
        mmOutputStream.write(msg.getBytes());
        myLabel.setText("Data Sent");
    }

    void closeBT() throws IOException
    {
        stopWorker = true;
        mmOutputStream.close();
        mmInputStream.close();
        mmSocket.close();
        myLabel.s`enter code here`etText("Bluetooth Closed");
    }
    }

---

在不计算的情况下很难判断第126行是什么，但快速估计它属于您的TextView setText分配。如果这是正确的，那么请确保您实际上在布局文件中找到了正确的文本视图

如果不是这一行，那么对于出现空指针的第126行，使用高亮显示的行进行更新可能会有所帮助

---

这可能是由于您加载了一个布局文件，而该文件不是您想要加载的，或者为TextView引用了错误的名称。

IMO该问题可能与函数findBT（）中的以下代码行有关

Set pairedDevices=mBluetoothAdapter.getBondedDevices（）；
如果（pairedDevices.size（）>0）
{
用于（蓝牙设备：pairedDevices）
{
if（device.getName（）.equals（“MattsBlueTooth”））
{
mmDevice=设备；
打破
}
}
}

---

“mmDevice”很可能未初始化。确保名称“MattsBlueTooth”是成对设备列表中显示的名称。否则使用配对设备列表中的一个。这意味着您必须先将蓝牙设备与android手机或平板电脑配对。

在此发布相关代码，请参阅我的编辑。我已经发布了我的代码。如果可以，请帮助我@如果可能的话，你也可以发布完整的错误消息吗？我已经发布了我的日志@杰斯奈德

07-01 12:03:16.474: E/AndroidRuntime(4301): FATAL EXCEPTION: main
07-01 12:03:16.474: E/AndroidRuntime(4301): java.lang.NullPointerException
07-01 12:03:16.474: E/AndroidRuntime(4301):     at com.example.blu1.MainActivity.openBT(MainActivity.java:126)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at com.example.blu1.MainActivity$1.onClick(MainActivity.java:61)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at android.view.View.performClick(View.java:4212)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at android.view.View$PerformClick.run(View.java:17476)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at android.os.Handler.handleCallback(Handler.java:800)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at android.os.Handler.dispatchMessage(Handler.java:100)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at android.os.Looper.loop(Looper.java:194)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at android.app.ActivityThread.main(ActivityThread.java:5371)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at java.lang.reflect.Method.invokeNative(Native Method)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at java.lang.reflect.Method.invoke(Method.java:525)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
07-01 12:03:16.474: E/AndroidRuntime(4301):     at dalvik.system.NativeStart.main(Native Method)

    Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
    if(pairedDevices.size() > 0)
    {
        for(BluetoothDevice device : pairedDevices)
        {
            if(device.getName().equals("MattsBlueTooth")) 
            {
                mmDevice = device;
                break;
            }
        }
    }