java - 应用程序已停止(Android Studio 蓝牙)

Question

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();
  }
}

Answer 1

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()。