android - App crashes while calling LocationUpdatesService with permission with NullPointerException

Question

I' trying to implement Google's android foreground location sample from github in my application. It works fine in the first run of the application. It requests for location permission and when the user grants permission, the service is starting flawlessly and fetches location.

But when the app runs the next time while it already has the permission, it crashes by showing a NullPointerException. I'm not able to narrow down the problem. What is different in the second run of the app which already has the permission? Getting error in OnStart() in mService.requestLocationUpdates(); line. Does it has to do anything with the package name that is declared in the LocationUpdatesService? or is it something else with permission? or with binding?

Stacktrace

2020-10-21 11:58:04.346 31805-31805/com.example.testapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.testapp, PID: 31805
    java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.testapp.LocationUpdatesService.requestLocationUpdates()' on a null object reference
        at com.example.testapp.EventsActivity.onStart(EventsActivity.java:237)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1391)
        at android.app.Activity.performStart(Activity.java:7348)
        at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3140)
        at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
        at 

android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
            at 

android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1950)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7073)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)
2020-10-21 11:58:04.367 31805-31805/com.example.testapp I/Process: Sending signal. PID: 31805 SIG: 9

MainActivity.java

 public class MainActivity extends AppCompatActivity implements
            SharedPreferences.OnSharedPreferenceChangeListener {
    
        //Location
        private static final String TAG = MainActivity.class.getSimpleName();
        // Used in checking for runtime permissions.
        private static final int REQUEST_PERMISSIONS_REQUEST_CODE = 34;
        // The BroadcastReceiver used to listen from broadcasts from the service.
        private MyReceiver myReceiver;
        // A reference to the service used to get location updates.
        private LocationUpdatesService mService = null;
        // Tracks the bound state of the service.
        private boolean mB

ound = false;
    // Monitors the state of the connection to the service.
    private final ServiceConnection mServiceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            LocationUpdatesService.LocalBinder binder = (LocationUpdatesService.LocalBinder) service;
            mService = binder.getService();
            mBound = true;
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            mService = null;
            mBound = false;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        myReceiver = new MyReceiver();
        // Check that the user hasn't revoked permissions by going to Settings.
        if (Utils.requestingLocationUpdates(this)) {
            if (!checkPermissions()) {
                requestPermissions();
            }
        }
        ....
        .....
    }


    @Override
    protected void onStart() {
        super.onStart();
        PreferenceManager.getDefaultSharedPreferences(this)
                .registerOnSharedPreferenceChangeListener(this);

        if (!checkPermissions()) {
            requestPermissions();
        } else {
            mService.requestLocationUpdates(); //CRASHING HERE
        }
        // Bind to the service. If the service is in foreground mode, this signals to the service
        // that since this activity is in the foreground, the service can exit foreground mode.
        bindService(new Intent(this, LocationUpdatesService.class), mServiceConnection,
                Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onStop() {
        if (mBound) {
            // Unbind from the service. This signals to the service that this activity is no longer
            // in the foreground, and the service can respond by promoting itself to a foreground
            // service.
            unbindService(mServiceConnection);
            mBound = false;
        }
        PreferenceManager.getDefaultSharedPreferences(this)
                .unregisterOnSharedPreferenceChangeListener(this);
        super.onStop();
    }

    /**
     * Returns the current state of the permissions needed.
     */
    private boolean checkPermissions() {
        return  PackageManager.PERMISSION_GRANTED == ActivityCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION);
    }

    private void requestPermissions() {
        boolean shouldProvideRationale =
                ActivityCompat.shouldShowRequestPermissionRationale(this,
                        Manifest.permission.ACCESS_FINE_LOCATION);

        // Provide an additional rationale to the user. This would happen if the user denied the
        // request previously, but didn't check the "Don't ask again" checkbox.
        if (shouldProvideRationale) {
            Log.i(TAG, "Displaying permission rationale to provide additional context.");
            Snackbar.make(
                    findViewById(R.id.sliding_layout),
                    R.string.permission_rationale,
                    Snackbar.LENGTH_INDEFINITE)
                    .setAction(R.string.ok, new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            // Request permission
                            ActivityCompat.requestPermissions(MainActivity.this,
                                    new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                                    REQUEST_PERMISSIONS_REQUEST_CODE);
                        }
                    })
                    .show();
        } else {
            Log.i(TAG, "Requesting permission");
            // Request permission. It's possible this can be auto answered if device policy
            // sets the permission in a given state or the user denied the permission
            // previously and checked "Never ask again".
            ActivityCompat.requestPermissions(MainActivity.this,
                    new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                    REQUEST_PERMISSIONS_REQUEST_CODE);
        }
    }

    /**
     * Callback received when a permissions request has been completed.
     */
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,
                                           @NonNull int[] grantResults) {
        Log.i(TAG, "onRequestPermissionResult");
        if (requestCode == REQUEST_PERMISSIONS_REQUEST_CODE) {
            if (grantResults.length <= 0) {
                // If user interaction was interrupted, the permission request is cancelled and you
                // receive empty arrays.
                Log.i(TAG, "User interaction was cancelled.");
            } else if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                // Permission was granted.
                mService.requestLocationUpdates();
            } else {
                // Permission denied.
                //setButtonsState(false);
                Snackbar.make(
                        findViewById(R.id.sliding_layout),
                        R.string.permission_denied_explanation,
                        Snackbar.LENGTH_INDEFINITE)
                        .setAction(R.string.settings, new View.OnClickListener() {
                            @Override
                            public void onClick(View view) {
                                // Build intent that displays the App settings screen.
                                Intent intent = new Intent();
                                intent.setAction(
                                        Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
                                Uri uri = Uri.fromParts("package",
                                        BuildConfig.APPLICATION_ID, null);
                                intent.setData(uri);
                                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                                startActivity(intent);
                            }
                        })
                        .show();
            }
        }
    }

    /**
     * Receiver for broadcasts sent by {@link LocationUpdatesService}.
     */
    private class MyReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            Location location = intent.getParcelableExtra(LocationUpdatesService.EXTRA_LOCATION);
            if (location != null) {
                Toast.makeText(MainActivity.this, Utils.getLocationText(location),
                        Toast.LENGTH_SHORT).show();
            }
        }
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String s) {
    }





    @Override
    protected void onResume() {
        LocalBroadcastManager.getInstance(this).registerReceiver(myReceiver,
                new IntentFilter(LocationUpdatesService.ACTION_BROADCAST));
        super.onResume();
        wakeLock.acquire();
    }

    @Override
    protected void onPause() {
        LocalBroadcastManager.getInstance(this).unregisterReceiver(myReceiver);
        super.onPause();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if(getBooleanFromSP("logOutBtnClicked")){
            stopService();
            mService.removeLocationUpdates();
        }else if(!getBooleanFromSP("logOutBtnClicked")){
            startService();
            mService.removeLocationUpdates();
        }
    }

}

LocationUpdatesService.java

public class LocationUpdatesService extends Service {

    private static final String PACKAGE_NAME =
            "com.google.android.gms.location.sample.locationupdatesforegroundservice";

    private static final String TAG = LocationUpdatesService.class.getSimpleName();

    /**
     * The name of the channel for notifications.
     */
    private static final String CHANNEL_ID = "channel_01";

    static final String ACTION_BROADCAST = PACKAGE_NAME + ".broadcast"

Answer 1

I am not sure, but try this:

@Override
    protected void onStart() {
        super.onStart();
        PreferenceManager.getDefaultSharedPreferences(this)
                .registerOnSharedPreferenceChangeListener(this);

        if (!checkPermissions()) {
            requestPermissions();
        } else if (mService != null) { // add null checker
            mService.requestLocationUpdates();
        }
        // Bind to the service. If the service is in foreground mode, this signals to the service
        // that since this activity is in the foreground, the service can exit foreground mode.
        bindService(new Intent(this, LocationUpdatesService.class), mServiceConnection,
                Context.BIND_AUTO_CREATE);
    }

Also:

private final ServiceConnection mServiceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            LocationUpdatesService.LocalBinder binder = (LocationUpdatesService.LocalBinder) service;
            mService = binder.getService();
            mService.requestLocationUpdates(); // also request it here
            mBound = true;
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            mService = null;
            mBound = false;
        }
    };