Loading SharedPreference giving NullPointerException

Question

I am trying to load string objects from my SharedPreference but I am getting a NullPointerException.. I am very new to this so I probably am not using it right.

The Error is in

loadPreferences

at

SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);

Here is my code,

public class OfflineActivity extends Activity implements NetworkObserver {

    public GeoPoint ourLocationGeoPoint;
    public List<PointOfInterest> pointList = new ArrayList<PointOfInterest>();
    SharedPreferences pointsToAddToServer;
    int index;

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

        //Load preferences
        loadPreferences();

        // Register for network status updates
        if (!NetworkStatus.isConnectedToInternet(getApplicationContext())) {
            NetworkStatus networkStatus = new NetworkStatus(this);
            networkStatus.addObserver(new OfflineActivity());
            Thread thread = new Thread(networkStatus);
            thread.start();
        }

        // Acquire a reference to the system Location Manager
        LocationManager locationManager = (LocationManager) this
                .getSystemService(Context.LOCATION_SERVICE);

        // Define a listener that responds to location updates
        LocationListener locationListener = new LocationListener() {

            public void onLocationChanged(Location location) {
                // Called when a new location is found by the network location
                // provider.
                /**
                 * Save Location to geopoint
                 */
                int lat = (int) (location.getLatitude() * 1E6);
                int lng = (int) (location.getLongitude() * 1E6);
                ourLocationGeoPoint = new GeoPoint(lat, lng);
            }

            public void onStatusChanged(String provider, int status,
                    Bundle extras) {
            }

            public void onProviderEnabled(String provider) {
            }

            public void onProviderDisabled(String provider) {
            }
        };
        for (String provider : locationManager.getAllProviders()) {
            // Register the listener with the Location Manager to receive
            // location updates
            locationManager.requestLocationUpdates(provider, 0, 0,
                    locationListener);
        }
    }

    /**
     * Add new location to database
     * 
     * @param view
     */
    public void addCurrentLocation(View view) {

        if (ourLocationGeoPoint != null) {

            LayoutInflater inflater = LayoutInflater.from(this);
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            view = inflater.inflate(R.layout.new_location_dialog, null);
            builder.setView(view);

            // Set fields
            final EditText titleBox = (EditText) view.findViewById(R.id.title);
            final EditText descriptionBox = (EditText) view
                    .findViewById(R.id.description);
            final RatingBar ratingBar = (RatingBar) view
                    .findViewById(R.id.ratingBar);
            final Spinner categoryDropdownMenu = (Spinner) view
                    .findViewById(R.id.categoryDropDown);

            // When User clicks Save
            builder.setPositiveButton("Save",
                    new DialogInterface.OnClickListener() {

                        public void onClick(DialogInterface dialog, int button) {

                            String title = titleBox.getText().toString();
                            String description = descriptionBox.getText()
                                    .toString();
                            String category = ("" + categoryDropdownMenu
                                    .getSelectedItem())
                                    .toLowerCase(Locale.ENGLISH);

                            int ratingNum = (int) ratingBar.getRating();
                            Log.d("User Setting title / description to: ",
                                    title + " : " + description);

                            // Create new Private Data field containing title /
                            // rating
                            PrivateField privateField = new PrivateField(
                                    "Michael", title, ratingNum);

                            // Create new point of Interest
                            PointOfInterest point = new PointOfInterest(
                                    category, description, ourLocationGeoPoint,
                                    privateField);

                            // Add to list to update later
                            Gson gson = new Gson();
                            String pointOfInterest = gson.toJson(point);

                            savePreferences(String.valueOf(index), pointOfInterest);
                            // Increase our index
                            index++;

                            Log.d("OfflineActivity", "Saving point "
                                    + point.latitude + ":" + point.longitude);
                            Toast.makeText(
                                    getBaseContext(),
                                    "Will add point \""
                                            + point.getTitle()
                                            + "\" when network connection has been made.",
                                    Toast.LENGTH_SHORT).show();
                        }
                    });

            // When User clicks cancel
            builder.setNegativeButton("Cancel",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            Log.d("Cancel setting Title & adding point", "");
                            return;
                        }
                    });

            builder.show();
        } else {
            Toast.makeText(this, "Could not determine location :(",
                    Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void updateStatus() {

        loadPreferences();
        SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();

        for (PointOfInterest poi : pointList) {
            UploadPointOfInterest uploadPointOfInterest = new UploadPointOfInterest(poi);
            uploadPointOfInterest.execute();
        }
        // Clear preferences, reset index
        editor.clear();
        editor.commit();
        index = 0;
    }

    /**
     * Save preferences
     * @param key
     * @param value
     */
    private void savePreferences(String key, String value) {
        SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putString(key, value);
        editor.commit();
    }

    /**
     * Load saved Preferences
     */
    private void loadPreferences() {
        SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE); <-- NullPointer here
        PointOfInterest temp;
        PointOfInterest point;
        Gson gson = new Gson();

        /**
         * Load all points from shared prefs
         */
        for(int x =0; ;x++) {
            index = x;
            if(sharedPreferences.contains(String.valueOf(x))){
                temp = gson.fromJson(sharedPreferences.getString(String.valueOf(x), null), PointOfInterest.class);
                point = new PointOfInterest(temp.getType(),temp.getDescription(),temp.getGeoPoint(),temp.getPrivateField());
                Log.d("Offline activity", "Loading point from sharedpref: " + point.getTitle());
                pointList.add(point);
            }
            else {
                break;
            }
        }

    }
}

and stack trace,

02-01 03:32:53.046: E/AndroidRuntime(30325): Uncaught handler: thread Thread-14 exiting due to uncaught exception
02-01 03:32:53.046: E/AndroidRuntime(30325): java.lang.NullPointerException
02-01 03:32:53.046: E/AndroidRuntime(30325):    at android.content.ContextWrapper.getPackageName(ContextWrapper.java:120)
02-01 03:32:53.046: E/AndroidRuntime(30325):    at android.app.Activity.getLocalClassName(Activity.java:3413)
02-01 03:32:53.046: E/AndroidRuntime(30325):    at android.app.Activity.getPreferences(Activity.java:3447)
02-01 03:32:53.046: E/AndroidRuntime(30325):    at com.example.mapproject.OfflineActivity.loadPreferences(OfflineActivity.java:207)
02-01 03:32:53.046: E/AndroidRuntime(30325):    at com.example.mapproject.OfflineActivity.updateStatus(OfflineActivity.java:177)
02-01 03:32:53.046: E/AndroidRuntime(30325):    at com.example.mapproject.NetworkStatus.notifyObservers(NetworkStatus.java:58)
02-01 03:32:53.046: E/AndroidRuntime(30325):    at com.example.mapproject.NetworkStatus.run(NetworkStatus.java:68)
02-01 03:32:53.046: E/AndroidRuntime(30325):    at java.lang.Thread.run(Thread.java:1096)
02-01 03:32:53.226: E/SemcCheckin(30325): Get crash dump level : java.io.FileNotFoundException: /data/semc-checkin/crashdump

Answer 1

The problem was here,

    // Register for network status updates
    if (!NetworkStatus.isConnectedToInternet(getApplicationContext())) {
        NetworkStatus networkStatus = new NetworkStatus(this);
        networkStatus.addObserver(new OfflineActivity()); <----
        Thread thread = new Thread(networkStatus);
        thread.start();
    }

Should have been:

    // Register for network status updates
    if (!NetworkStatus.isConnectedToInternet(getApplicationContext())) {
        NetworkStatus networkStatus = new NetworkStatus(this);
        networkStatus.addObserver(this); <----
        Thread thread = new Thread(networkStatus);
        thread.start();
    }

Answer 2

Since everyone isn't reading the comments, the OP's issue doesn't have to do with the preference saving, it has to do with the fact that they instantiated another Activity. Android doesn't work well with that since an Activity instantiated explictly via constructor is incomplete. All the op had to do was change

networkStatus.addObserver(new OfflineActivity());

to

networkStatus.addObserver(this);

So that Android doesn't create a new (bad) instance of the Activity.

Whenever you see something like:

java.lang.NullPointerException 02-01 03:32:53.046: E/AndroidRuntime(30325): at

android.content.ContextWrapper.getPackageName(ContextWrapper.java:120)

It usually has to do with behind the scenes operations (how could getPackageName() be null just like that?) caused by an explicit instantiaion.

Answer 3

public void savePreference(String stringToSave){
    Editor custom_editor = custom_editor.edit();
    custom_editor.putString(NameToSaveAs, stringToSave);
    custom_editor.commit();
}

public String getPreferences(){
    return yourPreferenceName.getString(NameToSaveAs, null);
}

you can modify this with your other todo things..