任何人都可以通过我的应用代码帮助我。我试图制作一个可以通过蓝牙将数据（数字或字母）发送到arduino的应用程序。这就是我的JAVA代码的外观：
package com.example.btprojektas;
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.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Set;
import java.util.UUID;
public class MainActivity extends Activity{
private static final String TAG = "btprojektas";
Button btnON, btnOFF;
BluetoothAdapter bluetoothAdapter = null;
BluetoothDevice device = null;
OutputStream outputStream = null;
BluetoothSocket socket = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
btnON = (Button) findViewById(R.id.btnON);
btnOFF = (Button) findViewById(R.id.btnOFF);
if(!bluetoothAdapter.isEnabled()){
Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBluetooth, 0);
}
loadPairedDevice();
connectBT();
btnON.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
sendData("0");
Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
}
});
btnOFF.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
sendData("1");
Toast.makeText(getBaseContext(), "Turn off LED", Toast.LENGTH_SHORT).show();
}
});
}
private void connectBT() {
if (device != null) {
UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb"); //Standard SerialPortService ID
try {
socket = device.createRfcommSocketToServiceRecord(uuid);
socket.connect();
outputStream = socket.getOutputStream();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private void disconnect() {
try {
if (outputStream != null) outputStream.close();
if (socket != null) socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
private void loadPairedDevice() {
Set<BluetoothDevice> pairedDevices = bluetoothAdapter.getBondedDevices();
if (pairedDevices.size() > 0) {
Log.d(TAG, "Device found");
for (BluetoothDevice device : pairedDevices)
if (device.getName().equals("HC-06")) {
this.device = device;
break;
}
}
}
@Override
protected void onPause() {
super.onPause();
disconnect();
}
@Override
protected void onResume() {
super.onResume();
loadPairedDevice();
connectBT();
}
private void sendData(String message) {
byte[] buffer = message.getBytes();
Log.d(TAG,"Send data:"+ message);
try{
outputStream.write (buffer);
} catch (IOException e) {}
}
}
XML中的我有两个按钮。当程序启动时，我按下其中一个按钮，出现“应用程序......意外停止”，并显示致命的错误代码：
01-08 15:55:15.439 15354-15354/com.example.btprojektas E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.btprojektas.MainActivity.sendData(MainActivity.java:122)
at com.example.btprojektas.MainActivity.access$000(MainActivity.java:22)
at com.example.btprojektas.MainActivity$1.onClick(MainActivity.java:55)
at android.view.View.performClick(View.java:2485)
at android.view.View$PerformClick.run(View.java:9080)
at android.os.Handler.handleCallback(Handler.java:587)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3687)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
at dalvik.system.NativeStart.main(Native Method)
P.S。对不起这个问题我知道这很常见，但我是编程特别是JAVA的新手。
答案 0 :(得分：0)
它是socket或outputStream。在ConnectBT中，您不检查套接字是否为空。假设socket有效，你直接调用socket.connect（）。这同样适用于outputStream。在确定它不为空之前使用它。
你也打电话
startActivityForResult(enableBluetooth, 0);
但是你没有检查蓝牙是否启用的结果。这会让您的设备产生怀疑。
致电
loadPairedDevice();
connectBT();
仅在启用蓝牙时才有意义。启用蓝牙可能需要几秒钟，但您可以立即调用它们。
答案 1 :(得分：0)
一些提示：
，捕获并打印您的异常：
try {
if (outputStream != null) {
outputStream.write(buffer);
}
else {
Log.d("TAG", "sendData() - outputStream is null!");
}
}
catch (IOException e) {
e.printStackTrace();
}
，如果找不到设备“HC-06”，则您的变量设备将为空...
启用蓝牙需要几秒钟，因此请注册并收听ACTION_STATE_CHANGED广播意图。它将包含额外的字段EXTRA_STATE;寻找STATE_ON，然后在那里调用你的loadPairedDevices（）和connectBT（）：
创建接收者（在您的MainActivity类中）：
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
//this is the action you are observing
if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
switch(state) {
//and the state we were looking for
//which means that bluetooth has switched on
//so now you can call your functions
//and set the flag to true, which then use in your
//onClick listeners
case BluetoothAdapter.STATE_ON:
loadPairedDevice();
connectBT();
isBluetoothOn = true;
break;
}
}
}
}
在onCreate（）中，创建IntentFilter并用它注册接收器
IntentFilter btFilter = new IntentFilter();
btFilter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(mReceiver, btFilter);
记得在onPause（）中取消注册接收器：
unregisterReceiver(mReceiver);
当你知道BT已经打开时，禁用你的按钮并在上面的监听器中启用它们;或者，保留一个标志并在你的点击监听器中使用它，例如：
boolean isBluetoothOn = false;
然后在获得STATE_ON
时在监听器中isBluetooth = true;
然后在按钮中单击监听器：
//for btnON
public void onClick(View v) {
if (isBluetoothOn) {
sendData("0");
Toast.makeText(getBaseContext(), "Turn on LED", Toast.LENGTH_SHORT).show();
}
}
为btnOFF做同样的事。