unlock screen programmatically not working

Question

I am making a small app in which when I draw my phone near to me the screen will lock itself and when I keep the phone far from me the phone will unlock itself. I used proximity sensor for this check. I can lock the screen when I put finger over the sensor. But I want the phone's screen lock to open when I move my finger away from the phone's sendor. I used DeviceManager for locking the screeen but its not unlocking it. I tried many suggestions in SO posts but none are working. The suggestion given in the link is also not working in my case. When I add that code in my onSensorChanged the phone's screen locks automatically.

public class MainActivity extends AppCompatActivity implements SensorEventListener {

    private DevicePolicyManager mgr=null;
    private ComponentName cn=null;
    private SensorManager mSensorManager;
    private Sensor mProximity;
    private static final int SENSOR_SENSITIVITY = 4;


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

        cn=new ComponentName(this, AdminReceiver.class);
        mgr=(DevicePolicyManager)getSystemService(DEVICE_POLICY_SERVICE);
        mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        mProximity = mSensorManager.getDefaultSensor(Sensor.TYPE_PROXIMITY);
    }

    @Override
    protected void onResume() {
        super.onResume();
        mSensorManager.registerListener(this, mProximity, SensorManager.SENSOR_DELAY_NORMAL);
    }

    @Override
    protected void onPause() {
        super.onPause();
        mSensorManager.unregisterListener(this);
    }


    public void lockMeNow(View v) {
        if (mgr.isAdminActive(cn)) {
            mgr.lockNow();
        }
        else {
            Intent intent = new Intent(DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);
            intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN, cn);
            intent.putExtra(DevicePolicyManager.EXTRA_ADD_EXPLANATION, getString(R.string.device_admin_explanation));
            startActivity(intent);
        }
    }


    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_PROXIMITY) {
            if (event.values[0] >= -SENSOR_SENSITIVITY && event.values[0] <= SENSOR_SENSITIVITY) {
                //Its near. Lock screen here                
                if (mgr.isAdminActive(cn)) {
                    mgr.lockNow();
                }else {
                    Intent intent = new Intent(DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);
                    intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN, cn);
                    intent.putExtra(DevicePolicyManager.EXTRA_ADD_EXPLANATION, getString(R.string.device_admin_explanation));
                    startActivity(intent);
                }
            } else {
                //Its far. Need to unlock here
                getWindow().addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED | WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON | WindowManager.LayoutParams.FLAG_ALLOW_LOCK_WHILE_SCREEN_ON);
            }
        }
    }

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

    }
}