如何在Android中将实时字符串保存到文件中

Question

我设计了一个Android应用程序，通过蓝牙从Arduino Due接收串行数据。我想将这些实时数据保存到文件中，并在我停止连接后读取该文件。我的程序没有任何错误，但是当我运行它时，我得到了“不幸的是，BT已停止”消息。我找不到错误。我很感激你的意见。

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.media.MediaScannerConnection;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Set;
import java.util.UUID;

public class MainActivity extends AppCompatActivity {

    TextView myLable;
    BluetoothDevice mmDevice;
    BluetoothAdapter mBluetoothAdapter;
    BluetoothSocket mmSocket;
    OutputStream mmOutputStream;
    InputStream mmInputStream;
    Thread workerThread;
    int readBufferPosition;
    volatile boolean stopWorker;
    byte[] readBuffer;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button openButton = findViewById(R.id.open);
        openButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try {
                    findBT();
                    openBT();
                    // readBT();
                } catch (IOException ex) {

                }
            }
        });


        Button closeButton = findViewById(R.id.close);
        closeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try{
                    closeBT();
                }catch (IOException ex){

                }
            }
        });

        Button readButton = findViewById(R.id.read);
        readButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                readFile();
            }
        });

        TextView myLable = findViewById(R.id.lable);
    }

    void findBT(){
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if(mBluetoothAdapter == null){
            myLable.setText("No bluetooth adapter available!!!");
        }
        if(!mBluetoothAdapter.isEnabled()){
            Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBluetooth, 0);
        }

        Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
        if(pairedDevices.size()> 0){
            for(BluetoothDevice device : pairedDevices){
                if(device.getName().equals("RNBT-744E")){
                    mmDevice = device;
                    break;
                }
            }
        }
        myLable.setText("Bluetooth Device Found :)");
    }

    void openBT() throws IOException{
        UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
        mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);
        mmSocket.connect();
        mmOutputStream = mmSocket.getOutputStream();
        mmInputStream =mmSocket.getInputStream();

        myLable.setText("Bluetooth Opened");
        readBT();
    }

    void readBT(){
        final Handler handler = new Handler();
        final byte delimiter = 10;
        stopWorker = false;
        readBufferPosition = 0;
        readBuffer = new byte[1024];

        workerThread = new Thread(new Runnable() {
            @Override
            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[] encodeBytes = new byte[readBufferPosition];
                                    System.arraycopy(readBuffer, 0, encodeBytes, 0, encodeBytes.length);
                                    final String data = new String (encodeBytes, "US-ASCII");
                                    readBufferPosition = 0;
                                    handler.post(new Runnable() {
                                        @Override
                                        public void run() {
                                            myLable.setText(data);
                                            saveToFile();
                                        }
                                    });
                                }
                            }
                        }
                    }catch (IOException ex){
                        stopWorker = true;
                    }


                }
            }
        });
        workerThread.start();
    }

    public void saveToFile(){
        String msg = myLable.getText().toString();
        try {
            File testFile = new File(this.getExternalFilesDir(null), "Elmira.txt");
            if(!testFile.exists()){
                testFile.createNewFile();

                BufferedWriter writer = new BufferedWriter(new FileWriter(testFile, true));
                writer.write(msg);
                writer.close();
                MediaScannerConnection.scanFile(this, new String[]{testFile.toString()}, null, null);
            }
        }catch (IOException e){
            Log.e("ReadWriteFile", "Unable to write to the testFile.txt file.");
        }
    }


    void closeBT() throws IOException {
        stopWorker = true;
        mmInputStream.close();
        mmSocket.close();
        myLable.setText("Bluetooth closed");
    }


    void readFile(){
        String textFromFile = "";
        File testFile = new File(this.getExternalFilesDir(null), "Elmira.txt");
        if(testFile != null){
            StringBuilder stringBuilder = new StringBuilder();
            BufferedReader reader = null;
            try{
                reader = new BufferedReader(new FileReader(testFile));
                String line;

                while((line = reader.readLine()) != null){
                    textFromFile += line.toString();
                    textFromFile += "\n";
                    myLable.setText(textFromFile);
                }reader.close();
            } catch(Exception e){
                Log.e("ReadWriteFile", "Unable to read the TestFile.txt file");
            }
        }
    }
}

Screenshot of App