我试过这段代码。但每次我按下按钮都会崩溃，我在LogCat中看到了：
致命的例外：主要 java.lang.NullPointer异常
虽然尝试此代码的每个人都说它非常完美！
任何人都有同样的问题吗？
谢谢！
这是代码：
package com.example.bluetoothexample;
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 BluetoothExampleActivity 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.activity_bluetooth_example);
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");
}
}
和.xml：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:ignore="TextFields,HardcodedText" >
<TextView
android:id="@+id/label"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Type here:" />
<EditText
android:id="@+id/entry"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@id/label"
android:background="@android:drawable/editbox_background" />
<Button
android:id="@+id/open"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_below="@id/entry"
android:layout_marginLeft="10dip"
android:text="Open" />
<Button
android:id="@+id/send"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@id/open"
android:layout_toLeftOf="@id/open"
android:text="Send" />
<Button
android:id="@+id/close"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@id/send"
android:layout_toLeftOf="@id/send"
android:text="Close" />
</RelativeLayout>
编辑：
这是堆栈跟踪trevor-e询问（推送openButton之后）：
04-16 18:24:10.919: V/Provider/Settings(13223): invalidate [system]: current 26 != cached 0
04-16 18:24:10.926: V/Provider/Settings(13223): from db cache, name = sound_effects_enabled , value = 0
04-16 18:24:10.941: D/AndroidRuntime(13223): Shutting down VM
04-16 18:24:10.941: W/dalvikvm(13223): threadid=1: thread exiting with uncaught exception (group=0x411a89a8)
04-16 18:24:10.947: E/AndroidRuntime(13223): FATAL EXCEPTION: main
04-16 18:24:10.947: E/AndroidRuntime(13223): java.lang.NullPointerException
04-16 18:24:10.947: E/AndroidRuntime(13223): at com.example.bluetoothexample.BluetoothExampleActivity.openBT(BluetoothExampleActivity.java:120)
04-16 18:24:10.947: E/AndroidRuntime(13223): at com.example.bluetoothexample.BluetoothExampleActivity$1.onClick(BluetoothExampleActivity.java:55)
04-16 18:24:10.947: E/AndroidRuntime(13223): at android.view.View.performClick(View.java:4211)
04-16 18:24:10.947: E/AndroidRuntime(13223): at android.view.View$PerformClick.run(View.java:17446)
04-16 18:24:10.947: E/AndroidRuntime(13223): at android.os.Handler.handleCallback(Handler.java:725)
04-16 18:24:10.947: E/AndroidRuntime(13223): at android.os.Handler.dispatchMessage(Handler.java:92)
04-16 18:24:10.947: E/AndroidRuntime(13223): at android.os.Looper.loop(Looper.java:153)
04-16 18:24:10.947: E/AndroidRuntime(13223): at android.app.ActivityThread.main(ActivityThread.java:5297)
04-16 18:24:10.947: E/AndroidRuntime(13223): at java.lang.reflect.Method.invokeNative(Native Method)
04-16 18:24:10.947: E/AndroidRuntime(13223): at java.lang.reflect.Method.invoke(Method.java:511)
04-16 18:24:10.947: E/AndroidRuntime(13223): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
04-16 18:24:10.947: E/AndroidRuntime(13223): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
04-16 18:24:10.947: E/AndroidRuntime(13223): at dalvik.system.NativeStart.main(Native Method)
04-16 18:24:11.009: I/Process(13223): Sending signal. PID: 13223 SIG: 9