我有一个 Android 应用程序，可以向 Arduino 设备发送数据或从 Arduino 设备检索数据。
package com.arduino.arduinoled1;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;
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.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
private static final String TAG = "Abdel-Domotic";
Button ledOn, ledOff;
Button gateOn, gateOff;
Button curtOn, curtOff;
Button getTemp;
TextView temp;
OutputStream mmOutputStream;
InputStream mmInputStream;
Thread workerThread;
byte[] readBuffer;
int readBufferPosition;
int counter;
volatile boolean stopWorker;
private static final int REQUEST_ENABLE_BT = 1;
private BluetoothAdapter btAdapter = null;
private BluetoothSocket btSocket = null;
private OutputStream outStream = null;
// Well known SPP UUID
private static final UUID MY_UUID =
UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
// Insert your server's MAC address
private static String address = "20:13:12:05:10:24";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d(TAG, "In onCreate()");
setContentView(R.layout.activity_main);
ledOn = (Button) findViewById(R.id.ledOn);
ledOff = (Button) findViewById(R.id.ledOff);
gateOn = (Button) findViewById(R.id.gateOn);
gateOff = (Button) findViewById(R.id.gateOff);
curtOn = (Button) findViewById(R.id.curtOn);
curtOff = (Button) findViewById(R.id.curtOff);
getTemp = (Button) findViewById(R.id.gettemp);
btAdapter = BluetoothAdapter.getDefaultAdapter();
checkBTState();
ledOn.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
sendData("1");
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked LED On", Toast.LENGTH_SHORT);
msg.show();
}
});
ledOff.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
sendData("0");
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked LED Off", Toast.LENGTH_SHORT);
msg.show();
}
});
gateOn.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
sendData("3");
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked Gate On", Toast.LENGTH_SHORT);
msg.show();
}
});
gateOff.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
sendData("2");
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked Gate Off", Toast.LENGTH_SHORT);
msg.show();
}
});
curtOn.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
sendData("5");
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked Curton On", Toast.LENGTH_SHORT);
msg.show();
}
});
curtOff.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
sendData("4");
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked Curton Off", Toast.LENGTH_SHORT);
msg.show();
}
});
getTemp.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
sendData("6");
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked Get Temperature", Toast.LENGTH_SHORT);
msg.show();
beginListenForData();
}
});
}
@Override
public void onResume() {
super.onResume();
Log.d(TAG, "...In onResume - Attempting client connect...");
// Set up a pointer to the remote node using it's address.
BluetoothDevice device = btAdapter.getRemoteDevice(address);
// Two things are needed to make a connection:
// A MAC address, which we got above.
// A Service ID or UUID. In this case we are using the
// UUID for SPP.
try {
btSocket = device.createRfcommSocketToServiceRecord(MY_UUID);
} catch (IOException e) {
errorExit("Fatal Error", "In onResume() and socket create failed: " + e.getMessage() + ".");
}
// Discovery is resource intensive. Make sure it isn't going on
// when you attempt to connect and pass your message.
btAdapter.cancelDiscovery();
// Establish the connection. This will block until it connects.
Log.d(TAG, "...Connecting to Remote...");
try {
btSocket.connect();
Log.d(TAG, "...Connection established and data link opened...");
} catch (IOException e) {
try {
btSocket.close();
} catch (IOException e2) {
errorExit("Fatal Error", "In onResume() and unable to close socket during connection failure" + e2.getMessage() + ".");
}
}
// Create a data stream so we can talk to server.
Log.d(TAG, "...Creating Socket...");
try {
outStream = btSocket.getOutputStream();
} catch (IOException e) {
errorExit("Fatal Error", "In onResume() and output stream creation failed:" + e.getMessage() + ".");
}
}
@Override
public void onPause() {
super.onPause();
Log.d(TAG, "...In onPause()...");
if (outStream != null) {
try {
outStream.flush();
} catch (IOException e) {
errorExit("Fatal Error", "In onPause() and failed to flush output stream: " + e.getMessage() + ".");
}
}
try {
btSocket.close();
} catch (IOException e2) {
errorExit("Fatal Error", "In onPause() and failed to close socket." + e2.getMessage() + ".");
}
}
private void checkBTState() {
// Check for Bluetooth support and then check to make sure it is turned on
// Emulator doesn't support Bluetooth and will return null
if(btAdapter==null) {
errorExit("Fatal Error", "Bluetooth Not supported. Aborting.");
} else {
if (btAdapter.isEnabled()) {
Log.d(TAG, "...Bluetooth is enabled...");
} else {
//Prompt user to turn on Bluetooth
Intent enableBtIntent = new Intent(btAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
}
}
private void errorExit(String title, String message){
Toast msg = Toast.makeText(getBaseContext(),
title + " - " + message, Toast.LENGTH_SHORT);
msg.show();
finish();
}
private void sendData(String message) {
byte[] msgBuffer = message.getBytes();
Log.d(TAG, "...Sending data: " + message + "...");
try {
outStream.write(msgBuffer);
} catch (IOException e) {
String msg = "In onResume() and an exception occurred during write: " + e.getMessage();
if (address.equals("00:00:00:00:00:00"))
msg = msg + ".\n\nUpdate your server address from 00:00:00:00:00:00 to the correct address on line 37 in the java code";
msg = msg + ".\n\nCheck that the SPP UUID: " + MY_UUID.toString() + " exists on server.\n\n";
errorExit("Fatal Error", msg);
}
}
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() {
temp.setText(data);
}
});
} else {
readBuffer[readBufferPosition++] = b;
}
}
}
} catch (IOException ex) {
stopWorker = true;
}
}
}
});
workerThread.start();
}
}
发送部分工作正常，但是当我尝试检索数据时，它给出以下错误消息
06-20 17:28:12.440: D/Abdel-Domotic(6718): ...Connection established and data link opened...
06-20 17:28:12.440: D/Abdel-Domotic(6718): ...Creating Socket...
06-20 17:28:15.470: D/Abdel-Domotic(6718): ...Sending data: 6...
06-20 17:28:15.470: D/BLZ20_ASOCKWRP(6718): asocket_write
06-20 17:28:15.470: I/BLZ20_WRAPPER(6718): blz20_wrp_poll: nfds 2, timeout -1 ms
06-20 17:28:15.470: D/BLZ20_WRAPPER(6718): blz20_wrp_poll: transp poll : (fd 43) returned r_ev [POLLOUT ] (0x4)
06-20 17:28:15.470: D/BLZ20_WRAPPER(6718): blz20_wrp_poll: return 1
06-20 17:28:15.470: D/BLZ20_WRAPPER(6718): blz20_wrp_write: wrote 1 bytes out of 1 on fd 43
06-20 17:28:15.490: W/dalvikvm(6718): threadid=9: thread exiting with uncaught exception (group=0x4001e578)
06-20 17:28:15.500: E/AndroidRuntime(6718): FATAL EXCEPTION: Thread-10
06-20 17:28:15.500: E/AndroidRuntime(6718): java.lang.NullPointerException
06-20 17:28:15.500: E/AndroidRuntime(6718): at com.arduino.arduinoled1.MainActivity$8.run(MainActivity.java:260)
06-20 17:28:15.500: E/AndroidRuntime(6718): at java.lang.Thread.run(Thread.java:1019)
06-20 17:28:15.530: D/Abdel-Domotic(6718): ...In onPause()...
06-20 17:28:15.530: D/BLZ20_ASOCKWRP(6718): asocket_abort [43,44,45]
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): blz20_wrp_shutdown: s 43, how 2
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): blz20_wrp_shutdown: fd (-1:43), bta 2, rc 1, wflags 0x800, cflags 0x0, port 9050
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): blz20_wrp_shutdown: shutdown socket
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): blz20_wrp_write: wrote 1 bytes out of 1 on fd 45
06-20 17:28:15.530: D/BLZ20_ASOCKWRP(6718): asocket_destroy
06-20 17:28:15.530: D/BLZ20_ASOCKWRP(6718): asocket_abort [43,44,45]
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): blz20_wrp_shutdown: s 43, how 2
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): blz20_wrp_shutdown: fd (-1:43), bta 2, rc 1, wflags 0x800, cflags 0x0, port 9050
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): blz20_wrp_shutdown: shutdown socket
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): blz20_wrp_write: wrote 1 bytes out of 1 on fd 45
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): blz20_wrp_close: s 45
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): blz20_wrp_close: std close (45)
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): blz20_wrp_close: s 44
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): blz20_wrp_close: std close (44)
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): blz20_wrp_close: s 43
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): blz20_wrp_close: fd (-1:43), bta 2, rc 1, wflags 0x800, cflags 0x0, port 9050
06-20 17:28:15.530: I/BLZ20_WRAPPER(6718): __close_prot_rfcomm: fd 43
06-20 17:28:15.530: I/BTL_IFC(6718): send_ctrl_msg: [BTL_IFC CTRL] send BTLIF_BTS_RFC_CLOSE (BTS) 8 pbytes (hdl 40)
06-20 17:28:15.530: D/BTL_IFC_WRP(6718): wrp_close_s_only: wrp_close_s_only [43] (43:-1) [brcm.bt.btlif]
06-20 17:28:15.530: D/BTL_IFC_WRP(6718): wrp_close_s_only: data socket closed
06-20 17:28:15.530: D/BTL_IFC_WRP(6718): wsactive_del: delete wsock 43 from active list [ad42cbd0]
06-20 17:28:15.530: D/BTL_IFC_WRP(6718): wrp_close_s_only: wsock fully closed, return to pool
06-20 17:28:15.530: D/BLZ20_WRAPPER(6718): btsk_free: success
我的第一个猜测是错误出现在第 260 行，其中表示 int bytesAvailable = mmInputStream.available();
我说得对吗？
有什么问题吗？我该如何修复它？
最佳答案
您的 mmInputStream 对象为 null。您忘记在使用该对象之前创建它。
关于java - Android - 从蓝牙读取数据时出错，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24331200/