Android - Write sensor readings into .txt file. UI freezes

Issue

Basically, I'm trying to write the sensor data into a .txt file in my SD card.

It works perfectly fine, when I set for (int i = 0; i % 2 == 0; i++), i.e., write the data into the .txt file every 2 samples.

But as shown in this code, I changed 5 to 1, i.e., I want every single sample to be written in the file. Once I run it, the UI freezes.

Anybody can help me to solve this?

Can it be fixed by creating another thread? (Is it accurate to say so?)

I'm new and thus only roughly know maybe the problem is due to the thread issue.

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import android.app.Activity;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity implements SensorEventListener {

    EditText txtData;
    Button startButton;
    Button stopButton;

    File myFile;
    FileOutputStream fOut;
    OutputStreamWriter myOutWriter;
    BufferedWriter myBufferedWriter;
    PrintWriter myPrintWriter;


    private SensorManager sensorManager;
    private long currentTime;
    private long startTime;

    float[] acceleration = new float[3];
    float[] rotationRate = new float[3];
    float[] magneticField = new float[3];

    boolean stopFlag = false;
    boolean startFlag = false;
    boolean isFirstSet = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // file name to be entered
        txtData = (EditText) findViewById(R.id.editText2);
        txtData.setHint("Enter File Name here...");

        // start button
        startButton = (Button) findViewById(R.id.button1);
        startButton.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // start recording the sensor data
                try {
                    myFile = new File("/sdcard/ResearchData/" + txtData.getText() + ".txt");
                    myFile.createNewFile();

                    fOut = new FileOutputStream(myFile);
                    myOutWriter = new OutputStreamWriter(fOut);
                    myBufferedWriter = new BufferedWriter(myOutWriter);
                    myPrintWriter = new PrintWriter(myBufferedWriter);

                    Toast.makeText(getBaseContext(), "Start recording the data set", Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                } finally {
                    startFlag = true;
                }
            }
        });

        // stop button
        stopButton = (Button) findViewById(R.id.button2);
        stopButton.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // stop recording the sensor data
                try {
                    stopFlag = true;
                    Toast.makeText(getBaseContext(), "Done recording the data set", Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
                }
            }
        });

        sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        if (startFlag) {

            if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
                acceleration[0] = event.values[0];
                acceleration[1] = event.values[1];
                acceleration[2] = event.values[2];
            }

            if (event.sensor.getType() == Sensor.TYPE_GYROSCOPE) {
                rotationRate[0] = event.values[0];
                rotationRate[1] = event.values[1];
                rotationRate[2] = event.values[2];
            }

            if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {
                magneticField[0] = event.values[0];
                magneticField[1] = event.values[1];
                magneticField[2] = event.values[2];
            }

            if (isFirstSet) {
                startTime = System.currentTimeMillis();
                isFirstSet = false;
            }

            currentTime = System.currentTimeMillis();

            for (int i = 0; i % 1 == 0; i++) {
                if (!stopFlag) {
                    save();
                }

                else {
                    try {
                        myOutWriter.close();
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch (NullPointerException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    try {
                        fOut.close();
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch (NullPointerException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    private void save() {

            myPrintWriter.write(currentTime - startTime + " " + acceleration[0] + " " + acceleration[1] + " " + acceleration[2]
                        + " " + rotationRate[0] + " " + rotationRate[1] + " " + rotationRate[2] 
                        + " " + magneticField[0] + " " + magneticField[1] + " " + magneticField[2] + "\n");
    }

    @Override
    protected void onResume() {
        super.onResume();
        // register this class as a listener for the sensors
        sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_NORMAL);
        sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_GYROSCOPE), SensorManager.SENSOR_DELAY_NORMAL);
        sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD), SensorManager.SENSOR_DELAY_NORMAL);
    }

    @Override
    protected void onPause() {
        // unregister listener
        super.onPause();
        sensorManager.unregisterListener(this);
    }

    @Override
    public void onAccuracyChanged(Sensor arg0, int arg1) {
        // TODO Auto-generated method stub

    }
}

Solution

it's better if you change your code to:

for(int i=0;i<1;i++){
    //your code to save
}

In your code, if you set the condition i%1==0, you loop enters in a endless loop...

Answered By - Manuel Pires