Android creating/stopping TimerTask

Question

I have an android application that makes submissions to a database every 3 minutes using a timer task. The timer is suppose to persist even if the user minimizes the application. If I change the focus to another app and then change back everything works correctly but if I press the home button and then press app Icon another timer task is started. Can anyone explain why?

package temp;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;
import android.location.Geocoder;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.PendingResult;
import com.google.android.gms.common.api.Status;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationServices;

import java.text.DateFormat;
import java.util.Date;
import java.util.Locale;

public class MainActivity extends Activity implements LocationListener,
        GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener{

    private Button bLogout, bWebsite;
    private ImageButton bLogData;
    private TextView etLabel;
    private UserLocalStore userLocalStore;
    private String mLastUpdateTime;
    private LocationRequest mLocationRequest;
    private GoogleApiClient mGoogleApiClient;
    private static final String TAG = "MainActivity";
    private static final long INTERVAL = 1000 * 15;
    private static final long FATEST_INTERVAL = 1000 * 30;
    private Geocoder geocoder;
    AddressOps addressOps;
    TimerUpdate timerUpdate;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.e(TAG, "On Create . . . . .");

        if(!isGooglePlayServicesAvailable()){
            startActivity(new Intent(MainActivity.this, login.class));
            finish();
            Toast.makeText(getApplicationContext(), "Please update GooglePlay Servies to use this Application", Toast.LENGTH_LONG).show();
        }else {
            mGoogleApiClient = new GoogleApiClient.Builder(this)
                    .addApi(LocationServices.API)
                    .addConnectionCallbacks(this)
                    .addOnConnectionFailedListener(this)
                    .build();

            createLocationRequest();
            userLocalStore = new UserLocalStore(this);
            this.geocoder = new Geocoder(MainActivity.this, Locale.getDefault());
            addressOps = new AddressOps(this.geocoder);

//            if(this.timerUpdate == null && authenticate() == true) {
//                this.timerUpdate = new TimerUpdate(this, addressOps);
//                timerUpdate.startTimer();
//            }

            etLabel = (TextView) findViewById(R.id.etEmailLabel);
            bLogout = (Button) findViewById(R.id.bLogout);
            bLogData = (ImageButton) findViewById(R.id.DataLog);
            bWebsite = (Button) findViewById(R.id.website);

            bLogData.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View arg0) {
                    String pressStatus = "3";
                    timerUpdate.update(pressStatus);
                }
            });

            bLogout.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View arg0) {
                    userLocalStore.clearuserData();
                    userLocalStore.setUserLoggedIn(false);
                    timerUpdate.stopTimerTask();
                    startActivity(new Intent(MainActivity.this, login.class));
                    finish();
                }
            });

            bWebsite.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View arg0) {
                    Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://temp.com"));
                    startActivity(browserIntent);
                }
            });
        }
    }

    private void displayUserDetails(){
        User user = userLocalStore.getLoggedInUser();
        String userdisplay = "Logged in as: " + user.username;
        etLabel.setText(userdisplay);
    }

    private boolean authenticate(){
        return userLocalStore.getUserLoggedIn();
    }

    private boolean isNetworkAvailable() {
        ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
        Log.e(TAG, "Network Check");
        return activeNetworkInfo != null && activeNetworkInfo.isConnected();
    }

    private boolean isGooglePlayServicesAvailable() {
        int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
        if (ConnectionResult.SUCCESS == status) {
            return true;
        } else {
            GooglePlayServicesUtil.getErrorDialog(status, this, 0).show();
            return false;
        }
    }

    protected  void createLocationRequest(){
        mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(INTERVAL);
        mLocationRequest.setFastestInterval(FATEST_INTERVAL);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
    }

    @Override
    public void onConnected(Bundle bundle) {
        Log.e(TAG, "onConnected: Connected - " + mGoogleApiClient.isConnected());
        startLocationUpdates();
    }

    protected void startLocationUpdates() {
        PendingResult<Status> pendingResult = LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
        Log.e(TAG, "Location update started ");
    }

    @Override
    public void onConnectionSuspended(int i) {
        stopLocationUpdates();
        Log.e(TAG, "On Connection Suspended " + mGoogleApiClient.isConnected());
        Toast.makeText(getApplicationContext(), "No Network Connection", Toast.LENGTH_LONG).show();
    }

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {
        Log.e(TAG, "Connection failed " + connectionResult.toString());
        stopLocationUpdates();
        Log.e(TAG, "onConnectionFailed " + mGoogleApiClient.isConnected());
        Toast.makeText(getApplicationContext(), "No Network Connection", Toast.LENGTH_LONG).show();
    }

    @Override
    public void onLocationChanged(Location location) {
        Log.e(TAG, "Firing onLocationChanged.........");
        if(this.timerUpdate != null) {
            timerUpdate.location = location;
        }else{
            Log.e(TAG, "Timer is null");
        }
        mLastUpdateTime = DateFormat.getTimeInstance().format(new Date());
    }

    protected void stopLocationUpdates() {
        LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
        Log.e(TAG, "Location update stopped");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.e(TAG, "MainActivity Paused");
    }

    @Override
    public void onResume() {
        super.onResume();
        Log.e(TAG, "MainActivity Resumed");
        if (mGoogleApiClient.isConnected()) {
            if(!isGooglePlayServicesAvailable()){
                startActivity(new Intent(MainActivity.this, login.class));
                Toast.makeText(getApplicationContext(), "Please update GooglePlay Servies to use this Application", Toast.LENGTH_LONG).show();
                finish();
            }
        }
    }

    @Override
    public void onStart() {
        super.onStart();

        if(authenticate() == true){
            displayUserDetails();
            if(this.timerUpdate == null) {
                this.timerUpdate = new TimerUpdate(this, addressOps);
                Log.e(TAG, "Timer created");
                timerUpdate.startTimer();
             }
        }else{
            startActivity(new Intent(MainActivity.this, login.class));
            finish();
        }

        mGoogleApiClient.connect();
        Log.e(TAG, "MainActivity Started, GoogleApi Connection:  " + mGoogleApiClient.isConnected());
    }

    @Override
    public void onStop() {
        super.onStop();
        Log.e(TAG, "MainActivity Stopped");
    }
}

Heres my timertask class

package temp;

import android.content.Context;
import android.location.Location;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Handler;
import android.util.Log;
import android.widget.Toast;

import java.util.Timer;
import java.util.TimerTask;

public class TimerUpdate {
    private Timer timer;
    private TimerTask timertask;
    public boolean timerScheduled = false;
    private final Handler handler = new Handler();
    private static final String TAG = "UpdateTimer";
    AddressOps addressOps;
    private Context mainContext;
    private UserLocalStore userLocalStore;
    public Location location;

    public TimerUpdate(Context context, AddressOps ops){
        initializeTimerTask();
        this.mainContext = context;
        this.addressOps = ops;
        userLocalStore = new UserLocalStore(context);
    }

    private void initializeTimerTask(){
        timertask = new TimerTask() {
            public void run(){
                handler.post(new Runnable(){
                    public void run(){
                        Log.e(TAG, "TimerTask Ran");
                        String status = "5";
                        update(status);
                    }
                });
            }
        };
    }

    public void startTimer(){
        timer = new Timer();
        timer.schedule(timertask, 1000 * 30, 1000 * 60 * 3);
        timerScheduled = true;
        Log.e(TAG, "Start Schedule created");
    }

    public void stopTimerTask(){
        if (timer != null){
            timer.cancel();
            timer = null;
            Log.e(TAG, "Timer Stopped");
        }
    }

    public void update(String status) {
        Log.e(TAG, "Update initiated .............");
        if (location != null) {
            double lat = location.getLatitude();
            double lng = location.getLongitude();

            if(isNetworkAvailable()){
                String address = addressOps.getAddressString(lng, lat);
                if(address != null) {
                    User user = userLocalStore.getLoggedInUser();
                    ServerRequest request = new ServerRequest(this.mainContext);
                    request.storeLocationInBackground(lat, lng, user.username, address, status);
                    Toast.makeText(this.mainContext, "Longitude: " + lng + "\nLatitude: "
                            + lat + "\nAddress: " + address, Toast.LENGTH_SHORT).show();
                }else{
                    Toast.makeText(this.mainContext, "Unable to retrieve Address", Toast.LENGTH_SHORT).show();
                }
            }else{
                Toast.makeText(this.mainContext, "No Network Connection" + "\nLatitude: " + lat
                        + "\nLongitude: " + lng, Toast.LENGTH_LONG).show();
            }

        } else {
            Log.e(TAG, "There is no current Location Data in Update");
            Toast.makeText(this.mainContext, "There is no current Location Data ....", Toast.LENGTH_SHORT).show();
        }
    }

    private boolean isNetworkAvailable() {
        ConnectivityManager connectivityManager = (ConnectivityManager)mainContext.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
        Log.e(TAG, "Network Check");
        return activeNetworkInfo != null && activeNetworkInfo.isConnected();
    }
}

Answer 1

When you restart your app, MainActivity goes through onCreate and onStart, and in onStart you start the timer.

Answer 2

So, as @Robert suggested in comments, this happens because your TimerTask instance is tied to the Activity instance. When you start another Activity instance (by starting your app by tapping the launcher icon), a new instance of TimerTask is created. If you need your TimerTask to be independent of Activities, then you'll need a Service.