我尝试使用蓝牙在两个设备之间进行通信，但当我尝试测试它时应用程序总是停止。 我只是尝试发送简单的字符串(例如“A”)，但也有错误。 我也无法手动打开/关闭蓝牙。
错误是:引起:java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“boolean android.bluetooth.BluetoothAdapter.isEnabled()” 在 com.example.pfe.reglages.onCreate(reglages.java:53)。
我需要帮助，因为这是我的毕业项目 谢谢。
夹带.java
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothServerSocket;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import android.os.Handler;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Set;
import java.util.UUID;
import android.os.Message;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import static android.bluetooth.BluetoothAdapter.getDefaultAdapter;
import static android.content.ContentValues.TAG;
public class entrainement extends AppCompatActivity {
private boolean CONTINUE_READ_WRITE = true;
private boolean CONNECTION_ENSTABLISHED = false;
private boolean DEVICES_IN_LIST = true;
private static String NAME = "pfe.fawez";
private static UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb");
Button btn6, btn7, btn8, btn16, btn9, btn5;
EditText txt;
TextView logview;
ListView lv;
ArrayList<String> listItems;
ArrayAdapter<String> listAdapter;
private BluetoothAdapter adapter;
private BluetoothSocket socket;
private InputStream is;
private OutputStream os;
private BluetoothDevice remoteDevice;
private Set<BluetoothDevice> pairedDevices;
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.entrainement);
btn6 = findViewById(R.id.button6);
btn7 = findViewById(R.id.button7);
btn8 = findViewById(R.id.button8);
btn16 = findViewById(R.id.button16);
btn9 = findViewById(R.id.button9);
btn5 = findViewById(R.id.button5);
txt = findViewById(R.id.editText2);
logview = findViewById(R.id.textView14);
lv = (ListView)findViewById(R.id.listView);
listItems = new ArrayList<String>(); //shows messages in list view
listAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, listItems);
lv.setAdapter(listAdapter);
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() //list onclick selection process
{
public void onItemClick(AdapterView<?> parent, View view, int position, long id)
{
if(DEVICES_IN_LIST)
{
String name = (String) parent.getItemAtPosition(position);
selectBTdevice(name); //selected device will be set globally
//Toast.makeText(getApplicationContext(), "Selected " + name, Toast.LENGTH_SHORT).show();
//do not automatically call OpenBT(null) because makes troubles with server/client selection
}
else //message is selected
{
String message = (String) parent.getItemAtPosition(position);
txt.setText(message);
}
}
/*adapter = BluetoothAdapter.getDefaultAdapter();
if (adapter == null) //If the adapter is null, then Bluetooth is not supported
{
Toast.makeText(this, "Bluetooth is not available", Toast.LENGTH_SHORT).show();
finish();
return;
}
list(null);*/
});
btn9.setOnClickListener(new View.OnClickListener() //sends text from text button
{
@Override
public void onClick(View v) {
String textToSend = txt.getText().toString();
byte[] b = textToSend.getBytes();
try {
os.write(b);
} catch (IOException e) {
Toast.makeText(getApplicationContext(), "Not sent", Toast.LENGTH_SHORT).show(); //usually problem server-client decision
}
logview.append("\nConnection !\n");
}
});
btn6.setOnClickListener(new View.OnClickListener() //sends text from text button
{
@Override
public void onClick(View v) {
String textToSend = "R";
byte[] b = textToSend.getBytes();
try {
os.write(b);
Toast.makeText(getApplicationContext(), "OK", Toast.LENGTH_SHORT).show();
} catch (IOException e) {
Toast.makeText(getApplicationContext(), "Not sent", Toast.LENGTH_SHORT).show(); //usually problem server-client decision
}
}
});
btn16.setOnClickListener(new View.OnClickListener() //sends text from text button
{
@Override
public void onClick(View v) {
String textToSend = "L";
byte[] b = textToSend.getBytes();
try {
os.write(b);
Toast.makeText(getApplicationContext(), "OK", Toast.LENGTH_SHORT).show();
} catch (IOException e) {
Toast.makeText(getApplicationContext(), "Not sent", Toast.LENGTH_SHORT).show(); //usually problem server-client decision
}
}
});
btn7.setOnClickListener(new View.OnClickListener() //sends text from text button
{
@Override
public void onClick(View v) {
String textToSend = "X";
byte[] b = textToSend.getBytes();
try {
os.write(b);
Toast.makeText(getApplicationContext(), "OK", Toast.LENGTH_SHORT).show();
} catch (IOException e) {
Toast.makeText(getApplicationContext(), "Not sent", Toast.LENGTH_SHORT).show(); //usually problem server-client decision
}
}
});
btn8.setOnClickListener(new View.OnClickListener() //sends text from text button
{
@Override
public void onClick(View v) {
String textToSend = "Y";
byte[] b = textToSend.getBytes();
try {
os.write(b);
Toast.makeText(getApplicationContext(), "OK", Toast.LENGTH_SHORT).show();
} catch (IOException e) {
Toast.makeText(getApplicationContext(), "Not sent", Toast.LENGTH_SHORT).show(); //usually problem server-client decision
}
}
});
}
private Runnable writter = new Runnable() {
@Override
public void run() {
while (CONTINUE_READ_WRITE) //reads from open stream
{
try
{
os.flush();
Thread.sleep(2000);
} catch (Exception e)
{
Log.e(TAG, "Writer failed in flushing output stream...");
CONTINUE_READ_WRITE = false;
}
}
}
};
public void list(View v) //shows paired devices to UI
{
CONNECTION_ENSTABLISHED = false; //protect from failing
listItems.clear(); //remove chat history
listAdapter.notifyDataSetChanged();
pairedDevices = adapter.getBondedDevices(); //list of devices
for(BluetoothDevice bt : pairedDevices) //foreach
{
listItems.add(0, bt.getName());
}
listAdapter.notifyDataSetChanged(); //reload UI
}
public void selectBTdevice(String name) //for selecting device from list which is used in procedures
{
if(pairedDevices.isEmpty()) {
list(null);
Toast.makeText(getApplicationContext(), "Selecting was unsucessful, no devices in list." ,Toast.LENGTH_SHORT ).show();
}
for(BluetoothDevice bt : pairedDevices) //foreach
{
if(name.equals(bt.getName()))
{
remoteDevice = bt;
Toast.makeText(getApplicationContext(), "Selected " + remoteDevice.getName(), Toast.LENGTH_SHORT ).show();
}
}
}
public void openBT(View v) //opens right thread for server or client
{
if(adapter == null)
{
adapter = getDefaultAdapter();
Log.i(TAG, "Backup way of getting adapter was used!");
}
CONTINUE_READ_WRITE = true; //writer tiebreaker
socket = null; //resetting if was used previously
is = null; //resetting if was used previously
os = null; //resetting if was used previously
if(pairedDevices.isEmpty() || remoteDevice == null)
{
Toast.makeText(this, "Paired device is not selected, choose one", Toast.LENGTH_SHORT).show();
return;
}
}
public void closeBT(View v) //for closing opened communications, cleaning used resources
{
/*if(adapter == null)
return;*/
CONTINUE_READ_WRITE = false;
CONNECTION_ENSTABLISHED = false;
if (is != null) {
try {is.close();} catch (Exception e) {}
is = null;
}
if (os != null) {
try {os.close();} catch (Exception e) {}
os = null;
}
if (socket != null) {
try {socket.close();} catch (Exception e) {}
socket = null;
}
try {
Handler mHandler = new Handler();
mHandler.removeCallbacksAndMessages(writter);
mHandler.removeCallbacksAndMessages(serverListener);
mHandler.removeCallbacksAndMessages(clientConnecter);
Log.i(TAG, "Threads ended...");
}catch (Exception e)
{
Log.e(TAG, "Attemp for closing threads was unsucessfull.");
}
Toast.makeText(getApplicationContext(), "Communication closed" ,Toast.LENGTH_SHORT).show();
list(null); //shows list for reselection
txt.setText(getResources().getString(R.string.demo));
}
private Runnable serverListener = new Runnable()
{
public void run()
{
try //opening of BT connection
{
android.util.Log.i("TrackingFlow", "Server socket: new way used...");
socket =(BluetoothSocket) remoteDevice.getClass().getMethod("createRfcommSocket", new Class[] {int.class}).invoke(remoteDevice,1);
socket.connect();
CONNECTION_ENSTABLISHED = true; //protect from failing
} catch(Exception e) //obsolete way how to open BT
{
try
{
android.util.Log.e("TrackingFlow", "Server socket: old way used...");
BluetoothServerSocket tmpsocket = adapter.listenUsingRfcommWithServiceRecord(NAME, MY_UUID);
socket = tmpsocket.accept();
CONNECTION_ENSTABLISHED = true; //protect from failing
android.util.Log.i("TrackingFlow", "Listening...");
}
catch (Exception ie)
{
Log.e(TAG, "Socket's accept method failed", ie);
ie.printStackTrace();
}
}
Log.i(TAG, "Server is ready for listening...");
runOnUiThread(new Runnable() {
@Override
public void run() { //Show message on UIThread
listItems.clear(); //remove chat history
listItems.add(0, String.format(" Server opened! Waiting for clients..."));
listAdapter.notifyDataSetChanged();
}});
try //reading part
{
is = socket.getInputStream();
os = socket.getOutputStream();
new Thread(writter).start();
int bufferSize = 1024;
int bytesRead = -1;
byte[] buffer = new byte[bufferSize];
while(CONTINUE_READ_WRITE) //Keep reading the messages while connection is open...
{
final StringBuilder sb = new StringBuilder();
bytesRead = is.read(buffer);
if (bytesRead != -1) {
String result = "";
while ((bytesRead == bufferSize) && (buffer[bufferSize-1] != 0))
{
result = result + new String(buffer, 0, bytesRead - 1);
bytesRead = is.read(buffer);
}
result = result + new String(buffer, 0, bytesRead - 1);
sb.append(result);
}
android.util.Log.e("TrackingFlow", "Read: " + sb.toString());
runOnUiThread(new Runnable() {
@Override
public void run() { //Show message on UIThread
Toast.makeText(entrainement.this, sb.toString(), Toast.LENGTH_SHORT).show();
listItems.add(0, String.format("< %s", sb.toString())); //showing in history
listAdapter.notifyDataSetChanged();
}
});
}
}
catch(IOException e){
Log.e(TAG, "Server not connected...");
e.printStackTrace();
}
}
};
private Runnable clientConnecter = new Runnable()
{
@Override
public void run()
{
try
{
socket = remoteDevice.createRfcommSocketToServiceRecord(MY_UUID);
socket.connect();
CONNECTION_ENSTABLISHED = true; //protect from failing
Log.i(TAG, "Client is connected...");
runOnUiThread(new Runnable() {
@Override
public void run() { //Show message on UIThread
listItems.clear(); //remove chat history
listItems.add(0, String.format(" ready to communicate! Write something..."));
listAdapter.notifyDataSetChanged();
}});
os = socket.getOutputStream();
is = socket.getInputStream();
new Thread(writter).start();
Log.i(TAG, "Preparation for reading was done");
int bufferSize = 1024;
int bytesRead = -1;
byte[] buffer = new byte[bufferSize];
while(CONTINUE_READ_WRITE) //Keep reading the messages while connection is open...
{
final StringBuilder sb = new StringBuilder();
bytesRead = is.read(buffer);
if (bytesRead != -1)
{
String result = "";
while ((bytesRead == bufferSize) && (buffer[bufferSize-1] != 0))
{
result = result + new String(buffer, 0, bytesRead - 1);
bytesRead = is.read(buffer);
}
result = result + new String(buffer, 0, bytesRead - 1);
sb.append(result);
}
android.util.Log.e("TrackingFlow", "Read: " + sb.toString());
runOnUiThread(new Runnable() {
@Override
public void run() { //Show message on UIThread
Toast.makeText(entrainement.this, sb.toString(), Toast.LENGTH_SHORT).show();
listItems.add(0, String.format("< %s", sb.toString()));
listAdapter.notifyDataSetChanged();
}
});
}
}
catch (IOException e)
{
Log.e(TAG, "Client not connected...");
e.printStackTrace();
}
}
};
}
reglages.java
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import java.util.Set;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
public class reglages extends AppCompatActivity {
private static final int REQUEST_ENABLE_BT = 0;
private static final int REQUEST_DISCOVER_BT = 1;
TextView mStatusBlueTv, mPairedTv;
ImageView mBlueIv;
Button mOnBtn, mOffBtn, mDiscoverBtn, mPairedBtn;
BluetoothAdapter mBlueAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.reglages);
mStatusBlueTv = findViewById(R.id.statusBluetoothTv);
mPairedTv = findViewById(R.id.pairedTv);
mBlueIv = findViewById(R.id.bluetoothIv);
mOnBtn = findViewById(R.id.onBtn);
mOffBtn = findViewById(R.id.offBtn);
mDiscoverBtn = findViewById(R.id.discoverableBtn);
mPairedBtn = findViewById(R.id.pairedBtn);
//adapter
mBlueAdapter = BluetoothAdapter.getDefaultAdapter();
//check if bluetooth is available or not
if (mBlueAdapter == null){
mStatusBlueTv.setText("Bluetooth is not available");
}
else {
mStatusBlueTv.setText("Bluetooth is available");
}
//set image according to bluetooth status(on/off)
if (mBlueAdapter.isEnabled()){
mBlueIv.setImageResource(R.drawable.ic_action_on);
}
else {
mBlueIv.setImageResource(R.drawable.ic_action_off);
}
//on btn click
mOnBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (!mBlueAdapter.isEnabled()){
showToast("Turning On Bluetooth...");
//intent to on bluetooth
Intent intent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(intent, REQUEST_ENABLE_BT);
}
else {
showToast("Bluetooth is already on");
}
}
});
//discover bluetooth btn click
mDiscoverBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (!mBlueAdapter.isDiscovering()){
showToast("Making Your Device Discoverable");
Intent intent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(intent, REQUEST_DISCOVER_BT);
}
}
});
//off btn click
mOffBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (mBlueAdapter.isEnabled()){
mBlueAdapter.disable();
showToast("Turning Bluetooth Off");
mBlueIv.setImageResource(R.drawable.ic_action_off);
}
else {
showToast("Bluetooth is already off");
}
}
});
//get paired devices btn click
mPairedBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (mBlueAdapter.isEnabled()){
mPairedTv.setText("Paired Devices");
Set<BluetoothDevice> devices = mBlueAdapter.getBondedDevices();
for (BluetoothDevice device: devices){
mPairedTv.append("\nDevice: " + device.getName()+ ", " + device);
}
}
else {
//bluetooth is off so can't get paired devices
showToast("Turn on bluetooth to get paired devices");
}
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
switch (requestCode){
case REQUEST_ENABLE_BT:
if (resultCode == RESULT_OK){
//bluetooth is on
mBlueIv.setImageResource(R.drawable.ic_action_on);
showToast("Bluetooth is on");
}
else {
//user denied to turn bluetooth on
showToast("could't on bluetooth");
}
break;
}
super.onActivityResult(requestCode, resultCode, data);
}
//toast message function
private void showToast(String msg){
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
}
}
最佳答案
然后更改此行:
//check if bluetooth is available or not
if (mBlueAdapter == null){
mStatusBlueTv.setText("Bluetooth is not available");
}
else {
mStatusBlueTv.setText("Bluetooth is available");
}
//set image according to bluetooth status(on/off)
if (mBlueAdapter.isEnabled()){
mBlueIv.setImageResource(R.drawable.ic_action_on);
}
else {
mBlueIv.setImageResource(R.drawable.ic_action_off);
}
对此:
//check if bluetooth is available or not
if (mBlueAdapter == null) {
mStatusBlueTv.setText("Bluetooth is not available");
mBlueIv.setImageResource(R.drawable.ic_action_off);
} else {
mStatusBlueTv.setText("Bluetooth is available");
//set image according to bluetooth status(on/off)
if (mBlueAdapter.isEnabled()) {
mBlueIv.setImageResource(R.drawable.ic_action_on);
} else {
mBlueIv.setImageResource(R.drawable.ic_action_off);
}
}
每次检查 isEnabled 时，首先检查是否为 null，然后更改:
if (mBlueAdapter.isEnabled()){
至:
if (mBlueAdapter != null && mBlueAdapter.isEnabled()) {
这样，当蓝牙不可用时(mBlueAdapter == null)，您就可以防止出现 NullPointers，因为在这种情况下您无法检查 isEnabled()。
关于java - 应用程序已停止(Android Studio 蓝牙)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/61428459/