Question

我必须从一个不是Android设备的蓝牙设备获取数据到Android手机。因此，作为Android手机中的接收器，我已经制作了一个应用程序来接收来自蓝牙设备的数据。我从这里的enter link description here

的帖子回答了一个教程

但我得到NullPointerException。谁能告诉我为什么我得到这个例外谁能告诉我如何在该代码中解决这个异常???

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");
    }
    }

我的日志：

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)

Answer 1

很难说出第126行没有计算，但快速估计它属于TextView setText赋值。如果这是正确的，那么请确保您实际上正确地在布局文件中找到文本视图。

如果不是这一行，那么对于第126行出现Nullpointer的问题突出显示的行可能会有所帮助。

这可能是因为您加载的布局文件并不意味着加载或引用TextView的错误名称。

Answer 2

IMO问题可能出在函数findBT（）中的以下代码行。

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

很可能'mmDevice'没有初始化。确保名称“MattsBlueTooth”是出现在配对设备列表中的名称。否则使用配对设备列表中的一个。这意味着您必须首先将BlueTooth设备与Android手机或平板电脑配对。

从蓝牙接收数据时获取NullPointerException

2 个答案: