Question

所以我按照本教程How to receive serial data using android bluetooth 我完全按照说的做了。但不知何故，应用程序在点击任何按钮后崩溃了。我的问题是，

1）为什么会发生这种情况？我的意思是，如果该应用程序在过去的ADT中运行良好，为什么它在最近的ADT中没有？这是什么原因？因为我发现某些人也有类似问题来自代码http://bellcode.wordpress.com/2012/01/02/android-and-arduino-bluetooth-communication/

的来源

2）我怎么能解决这个问题？我相信代码已经结构良好，首先初始化按钮然后设置onclicklistener

3）有人可以告诉这个日志应该是什么意思吗？我是Android编程的新手这里我包括报告崩溃的logcat，

11-13 09:26:44.711 E/AndroidRuntime(14902): FATAL EXCEPTION: main
11-13 09:26:44.711 E/AndroidRuntime(14902): java.lang.NullPointerException
11-13 09:26:44.711 E/AndroidRuntime(14902):     at com.example.androidarduinopackage.MainActivity.closeBT(MainActivity.java:207)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at com.example.androidarduinopackage.MainActivity$3.onClick(MainActivity.java:90)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at android.view.View.performClick(View.java:3517)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at android.view.View$PerformClick.run(View.java:14155)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at android.os.Handler.handleCallback(Handler.java:605)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at android.os.Handler.dispatchMessage(Handler.java:92)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at android.os.Looper.loop(Looper.java:154)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at android.app.ActivityThread.main(ActivityThread.java:4624)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at java.lang.reflect.Method.invokeNative(Native Method)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at java.lang.reflect.Method.invoke(Method.java:511)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576)
11-13 09:26:44.711 E/AndroidRuntime(14902):     at dalvik.system.NativeStart.main(Native Method)

代码：

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.setText("Bluetooth Closed");
}
}

Answer 1

closeBT方法中的一个或多个这些对象为null：mOutputStream，mmInputStream，mmSocket。您应该验证这些对象不是null。如果mmSocket为null，您应该检查为什么此对象不是inicialized。可能是与蓝牙适配器相关的东西或您正在使用的代码与android的版本不兼容。

单击按钮后应用程序崩溃（logcat包含）

1 个答案: