Gravity sensor listener not working

Question

I want to get accelerometer sensor data which is in earth axis through a service. I read about a way to do it as well on one of the posts on stackoverflow. But I have an issue.

@Override
public void onSensorChanged(SensorEvent event) {
    Toast.makeText(this, "Hollyy shiiitt",Toast.LENGTH_SHORT);
    String acceldata = "";

    float[] gravityValues = null;
    float[] magneticValues = null;

    if (event.sensor.getType() == Sensor.TYPE_GRAVITY) {
        gravityValues = event.values.clone();
        Toast.makeText(this, "The gra data is " + String.valueOf(gravityValues), Toast.LENGTH_SHORT);
    }

    if ((gravityValues != null) && (magneticValues != null)
            && (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)) {

        // float for use in conversion device relative acceleration to earth axis acceleration
        float[] deviceRelativeAcceleration = new float[4];
        deviceRelativeAcceleration[0] = event.values[0];
        deviceRelativeAcceleration[1] = event.values[1];
        deviceRelativeAcceleration[2] = event.values[2];
        deviceRelativeAcceleration[3] = 0;

        // Change the device relative acceleration values to earth relative values
        // X axis -> East
        // Y axis -> North Pole
        // Z axis -> Sky

        float[] R = new float[16], I = new float[16], earthAcc = new float[16];

        SensorManager.getRotationMatrix(R, I, gravityValues, magneticValues);

        float[] inv = new float[16];

        android.opengl.Matrix.invertM(inv, 0, R, 0);
        android.opengl.Matrix.multiplyMV(earthAcc, 0, inv, 0, deviceRelativeAcceleration, 0);

        acceldata = String.valueOf(lat) + "," + String.valueOf(lon) + "," +  String.valueOf(speed)+","+ String.valueOf(earthAcc[0]) + "," + String.valueOf(earthAcc[1]) + "," + String.valueOf(earthAcc[2])+ "," + String.valueOf(event.values[0])+ "," + String.valueOf(event.values[1])+ "," + String.valueOf(event.values[2]);

    }

    //SDK  version check
    if(Build.VERSION.SDK_INT > 18) {
        File file;
        FileWriter filew; // Internal Storage writing
        try {
            file = new File(getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS) + "/" + filename); //Android 4.4 and above
            filew = new FileWriter(file, true); //true for append
            filew.write(acceldata + String.valueOf(gravityValues) + String.valueOf(magneticValues) +      "\n");
            filew.close();


        } catch (Exception e) {
            e.printStackTrace();

        }
    }
    else{
        String data = acceldata + "\n"  ;
        try {
            FileOutputStream fOut = openFileOutput("/" + filename,Context.MODE_APPEND);
            fOut.write(data.getBytes());
            fOut.close();
            Toast.makeText(getBaseContext(),"file saved",Toast.LENGTH_SHORT).show();
        } catch (IOException e) {
            e.printStackTrace();
            Toast.makeText(getBaseContext(),"file not saved API < 19",Toast.LENGTH_SHORT).show();
        }
    }

}

The if statement for gravity sensor on location changed doesn't return any value so the next statement also doesn't work as gravityValues has a null value.

The sensors registered are

mAccelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
mMagnetsensor = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
mGravity = sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY);

They are then registered as

int SamplingFrequency = 2 * 100000; // delay in microsecond. in this case 0.2 second
sensorManager.registerListener(this, mAccelerometer,SamplingFrequency);
sensorManager.registerListener(this, mMagnetsensor, SamplingFrequency);
sensorManager.registerListener(this,mGravity,SamplingFrequency);

I am a newbie in app development so any help would be appreciated.

Answer 1

Your device probably does not have gravity sensor. Check if it's available

if (mSensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY) != null) {
        Toast.makeText(ActivitySensor1Availability.this, "Gravity AVAILABLE", Toast.LENGTH_SHORT).show();
    } else {
        // Failure! No Gravity Sensor.
        Toast.makeText(ActivitySensor1Availability.this, "Failure! No Gravity Sensor", Toast.LENGTH_SHORT).show();
    }