NullPointerException异常

问题描述：

所以我的代码一直在正常工作，并且我为GUI添加了一些额外的功能，现在突然间我得到一个空指针异常。我无法弄清楚为了做到这一点，我可以改变什么。我已经把代码弄糟了，直到错误出现的地方。NullPointerException异常

public class AndroidBluetooth extends Activity { 

/** Called when the activity is first created. */ 
private static BluetoothAdapter myBtAdapter; 
private static BluetoothDevice myBtDevice; 
private ArrayAdapter<String> btArrayAdapter; 
private ArrayList<BluetoothDevice> btDevicesFound = new ArrayList<BluetoothDevice>(); 
private Button btnScanDevice; 
private TextView stateBluetooth; 
private ListView listDevicesFound; 
private InputStream iStream; 
private OutputStream oStream; 
private BluetoothSocket btSocket; 
private String newDeviceAddress; 
private BroadcastReceiver mReceiver; 

// Intent request codes 
private static final int REQUEST_CONNECT_DEVICE = 1; 

private static TextView mTitle; 

// Name of the connected device 
private String mConnectedDeviceName = null; 

/** 
* Set to true to add debugging code and logging. 
*/ 
public static final boolean DEBUG = true; 

/** 
* Set to true to log each character received from the remote process to the 
* android log, which makes it easier to debug some kinds of problems with 
* emulating escape sequences and control codes. 
*/ 
public static final boolean LOG_CHARACTERS_FLAG = DEBUG && false; 

/** 
* Set to true to log unknown escape sequences. 
*/ 
public static final boolean LOG_UNKNOWN_ESCAPE_SEQUENCES = DEBUG && false; 

private static final int REQUEST_ENABLE_BT = 2; 


// Member fields 
//private final BluetoothAdapter mAdapter; 
//private final Handler mHandler; 
//private ConnectThread mConnectThread; 
//private ConnectedThread mConnectedThread; 
//private int mState; 

//private EmulatorView mEmulatorView; 

// Constants that indicate the current connection state 
public static final int STATE_NONE = 0;  // we're doing nothing 
public static final int STATE_LISTEN = 1;  // now listening for incoming connections 
public static final int STATE_CONNECTING = 2; // now initiating an outgoing connection 
public static final int STATE_CONNECTED = 3; // now connected to a remote device 

//public boolean customTitleSupported; 
@Override 
public void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 

    //customTitleSupported = requestWindowFeature(Window.FEATURE_CUSTOM_TITLE); 
    // Set up window View 
    setContentView(R.layout.main); 

    stateBluetooth = (TextView) findViewById (R.id.titleTvRight); 
    startBluetooth(); 
    myBtAdapter = null; 
    CheckBlueToothState(); 

    //customTitleBar(getText(R.string.app_name).toString(), getText(R.string.app_name).toString()); 
} 
/** 
public void customTitleBar(String left, String right) { 
    if(right.length() > 20) right = right.substring(0, 20); 

    if(customTitleSupported) { 
     getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.customlayoutbar); 
     TextView titleTvLeft = (TextView) findViewById(R.id.titleTvLeft); 
     TextView titleTvRight = (TextView) findViewById(R.id.titleTvRight); 

     titleTvLeft.setText(left); 
     titleTvRight.setText(right); 

    } 
} 
*/ 
public boolean onCreateOptionsMenu(Menu menu) { 
    MenuInflater inflater = getMenuInflater(); 
    inflater.inflate(R.menu.option_menu, menu); 
    return true; 
} 

public boolean onOptionsItemSelected(MenuItem item) { 
    switch(item.getItemId()) { 
    case R.id.connect: 
     startActivityForResult(new Intent(this, DeviceList.class), REQUEST_CONNECT_DEVICE ); 
     return true; 
    case R.id.preferences: 
     return true; 
    default: 
     return super.onContextItemSelected(item); 
    } 
} 

private void CheckBlueToothState() { 
    Log.i("HUH", "0"); 
    if(myBtAdapter == null) { 
     Log.i("HUH", "1"); 
     stateBluetooth.setText("Bluetooth NOT supported"); 
    } else { 
     Log.i("HUH","2"); 
     if(myBtAdapter.isEnabled()) { 
      Log.i("HUH","3"); 
      if(myBtAdapter.isDiscovering()) { 
       Log.i("HUH","4"); 
       stateBluetooth.setText("Bluetooth is currently " + 
         "in device discovery process."); 
      } else { 
       Log.i("HUH","5"); 
       stateBluetooth.setText("Bluetooth is Enabled."); 
       btnScanDevice.setEnabled(true); 
      } 
     } else { 
      Log.i("HUH","6"); 
      stateBluetooth.setText("Bluetooth is NOT enabled"); 
      Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); 
      startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT); 
     } 
    } 
} 

private Button.OnClickListener btnScanDeviceOnClickListener = new Button.OnClickListener() { 
    public void onClick(View arg0) { 

    } 
}; 


@Override 
protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
    if(requestCode == REQUEST_ENABLE_BT) { 
     CheckBlueToothState(); 
    } 
} 

//In SDK15 (4.0.3) this method is now public as 
//Bluetooth.fetchUuisWithSdp() and BluetoothDevice.getUuids() 
public ParcelUuid[] servicesFromDevice(BluetoothDevice device) { 
    try { 
     Class cl = Class.forName("android.bluetooth.BluetoothDevice"); 
     Class[] par = {}; 
     Method method = cl.getMethod("getUuids", par); 
     Object[] args = {}; 
     ParcelUuid[] retval = (ParcelUuid[]) method.invoke(device, args); 
     return retval; 
    } catch (Exception e) { 
     e.printStackTrace(); 
     return null; 
    } 
} 

private final BroadcastReceiver ActionFoundReceiver = new BroadcastReceiver() { 
    public void onReceive(Context context, Intent intent) { 
     String action = intent.getAction(); 
     if(BluetoothDevice.ACTION_FOUND.equals(action)) { 
      BluetoothDevice btDevice = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE); 
      btDevicesFound.add(btDevice); 
      btArrayAdapter.add(btDevice.getName() + "\n" + btDevice.getAddress()); 
      btArrayAdapter.notifyDataSetChanged(); 
     }   
    } 
}; 
public static void startBluetooth(){ 
    try { 
     myBtAdapter = BluetoothAdapter.getDefaultAdapter(); 
     myBtAdapter.enable(); 
    } catch (NullPointerException ex) { 
     Log.e("Bluetooth", "Device not available"); 
    } 
} 

public static void stopBluetooth() { 
    myBtAdapter.disable(); 
}

}

这里是logcat的：

06-13 16:34:33.654: I/HUH(17008): 0 
06-13 16:34:33.654: I/HUH(17008): 1 
06-13 16:34:33.662: D/AndroidRuntime(17008): Shutting down VM 
06-13 16:34:33.662: W/dalvikvm(17008): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
06-13 16:34:33.662: E/AndroidRuntime(17008): FATAL EXCEPTION: main 
06-13 16:34:33.662: E/AndroidRuntime(17008): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.exercise.AndroidBluetooth/com.exercise.AndroidBluetooth.AndroidBluetooth}: java.lang.NullPointerException 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.os.Handler.dispatchMessage(Handler.java:99) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.os.Looper.loop(Looper.java:130) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.app.ActivityThread.main(ActivityThread.java:3683) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at java.lang.reflect.Method.invokeNative(Native Method) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at java.lang.reflect.Method.invoke(Method.java:507) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at dalvik.system.NativeStart.main(Native Method) 
06-13 16:34:33.662: E/AndroidRuntime(17008): Caused by: java.lang.NullPointerException 
06-13 16:34:33.662: E/AndroidRuntime(17008): at com.exercise.AndroidBluetooth.AndroidBluetooth.CheckBlueToothState(AndroidBluetooth.java:165) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at com.exercise.AndroidBluetooth.AndroidBluetooth.onCreate(AndroidBluetooth.java:124) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
06-13 16:34:33.662: E/AndroidRuntime(17008): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
06-13 16:34:33.662: E/AndroidRuntime(17008): ... 11 more

什么行是165？（'CheckBlueToothState（AndroidBluetooth.java:165）'）？ – Nanne

'stateBluetooth'似乎是'null'。 'R.lay.main'中是否存在'R.id.titleTvRight'？ – Floern

如果R.id.titleTv确实像Foern提到的那样存在，请尝试将onCreate（）逻辑的其余部分放在onFinishInflate（） –

答

我希望你已经发布了全班...我们不知道你是否切断了原因......例如，一个可能的原因;

是stateBluetooth声明为类变量还是局部变量？如果你滑倒并在onCreate中创建它，那可能就是为什么你使用另一种方法获得NPE的原因。

我刚刚添加了我的其他代码，对此感到抱歉。 – JuiCe

答

由于CheckBluetoothState（）是问题区域和堆栈跟踪不给多的信息，请尝试用尝试捕捉周围并打印整个错误。也可以尝试通过在每个点捕获异常来调试它。有了很少的信息，这就是我所能想到的。通过从catch块中发布错误来更新问题。希望这可以帮助。

那么LogCat说NullPointerException，并在其行165.这是行“stateBluetooth.setText（”蓝牙不支持“）;” CheckBluetoothState内 – JuiCe

答

myBtAdapter = null;，我有这个初始化的问题

所以将其更改为：

myBtAdapter = BluetoothAdapter.getDefaultAdapter;

宾果！

NullPointerException异常

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