How to add data to an existing .txt file in android

Question

I am developing an application that reads data coming from the accelerometer and I want to save them in .txt file, so that I can later process them.

So far I have been able to get the readings and also to save just one reading, as from what I understand I always create a new file that overwrites the previously existing file. But I want is to have all the measurements from the moment I push the start button, until I push the stop button.

Here is the code I'm using:

public class MainActivity extends AppCompatActivity implements SensorEventListener, View.OnClickListener {

private SensorManager mSensorManager;

private Sensor mAccelerometer;
private Button bStart, bStop;
float[] acceleration = new float[3];
private String mString;

MyFile file = new MyFile(this);


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

    bStart = (Button)findViewById(R.id.start);
    bStop = (Button)findViewById(R.id.stop);

    mSensorManager=(SensorManager)getSystemService(SENSOR_SERVICE);
    mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

    bStart.setOnClickListener(this);
    bStop.setOnClickListener(this);
    bStart.setEnabled(true);
    bStop.setEnabled(false);
}

@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {}

public final void onSensorChanged(SensorEvent event){
    if(event.sensor.getType() ==  Sensor.TYPE_ACCELEROMETER){
        acceleration[0] = event.values[0];
        acceleration[1] = event.values[1];
        acceleration[2] = event.values[2];
        TextView mTextview1 = (TextView) findViewById(R.id.textView1);
        TextView mTextview2 = (TextView) findViewById(R.id.textView2);
        TextView mTextview3 = (TextView) findViewById(R.id.textView3);
        mTextview1.setText("X:"+String.valueOf( acceleration[0]));
        mTextview2.setText("Y:"+String.valueOf( acceleration[1]));
        mTextview3.setText("Z:"+String.valueOf( acceleration[2]));

        file.writeToSD(acceleration[0] + "," +acceleration[1] + "," +acceleration[2] + "\n");
    }
}

@Override
public void onClick(View v) {
    switch(v.getId()){
        case R.id.start:
            bStart.setEnabled(false);
            bStop.setEnabled(true);
            mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
            break;
        case R.id.stop:
            bStart.setEnabled(true);
            bStop.setEnabled(false);
            mSensorManager.unregisterListener(this);
            break;
    }
}

}

And MyFile Class, where the job gets done is the following:

public class MyFile {

String TAG = "MyFile";
Context context;

public MyFile(Context context) {
    this.context = context;
}

public Boolean writeToSD(String text) {
    Boolean write_successful = false;
    File root = null;
    try {
        // check for SDcard
        root = Environment.getExternalStorageDirectory();
        Log.i(TAG, "path.." + root.getAbsolutePath());

        //check sdcard permission
        if (root.canWrite()) {
            File fileDir = new File(root.getAbsolutePath());
            fileDir.mkdirs();

            File file = new File(fileDir, "samplefile.txt");
            FileWriter filewriter = new FileWriter(file);
            BufferedWriter out = new BufferedWriter(filewriter);
            out.append(text);
            out.flush();
            out.close();
            write_successful = true;
        }
    } catch (IOException e) {
       e.printStackTrace();
        write_successful = false;
    }
    return write_successful;
}

}

Another question that I have is why I can not store the .txt file in the sdcard and it is saved in the internal memory.

Thank you for your time and your help

Pass 2nd parameter true to append in file. Like this FileWriter fw = new FileWriter("outfilename", true); — Wasim K. Memon, Apr 25 '16 at 03:32
Thank you very much. It worked. By the way, can I ask you why using this code the .txt file is saved in the internal memory of the device and not in the sdcard? I have used the permissions — user2149122, Apr 25 '16 at 09:39
you are testing in emulator or device ? you can check what path it prints in logger. you have already printed that path. so check it. — Wasim K. Memon, Apr 25 '16 at 09:48
It gives back a path in the internal memory. I can not figure out why this is happening. And I'm testing on both. In the actual device I find the file in the internal memory. In the emulator I do not have access to the internal memory — user2149122, Apr 25 '16 at 09:53
for that you can check this - http://stackoverflow.com/a/6049446/2128166 — Wasim K. Memon, Apr 25 '16 at 10:02

score 5 · Accepted Answer · answered Apr 25 '16 at 07:07

Try this code. Set second argument of FileWriter to true. Thus you can append your existing file

 File file = new File("Hello.txt");    
 file.createNewFile();    
 FileWriter writer = new FileWriter(file,true); 
 writer.write("Writes the content to the file"); 
 writer.flush();
 writer.close();

How to add data to an existing .txt file in android

1 Answers1