Question

As the title says I get a NullPointerException when I try to get a list from a database. Here is the code:

public List<String> getAllRockBands() {
     List<String> bandList = new ArrayList<String>();

     String selection = BAND_GENRE + "=1";

     SQLiteDatabase db = sqLiteHelper.getReadableDatabase();
     Cursor cursor = db.query(BANDDATABASE_TABLE,new String[]{BAND_NAME}, selection, null, null, null, BAND_NAME);

     int index = cursor.getColumnIndex(BAND_NAME);

     if (cursor.moveToFirst()) {
         do {
          String bandName = cursor.getString(index);
             bandList.add(bandName);
         } while (cursor.moveToNext());
     }

     return bandList;
 }

`

public class RockAllFragment extends SherlockListFragment {

    private BandDatabaseAdapter mySQLiteAdapter;
    private List<String> bandList = mySQLiteAdapter.getAllRockBands();

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    return inflater.inflate(R.layout.my_list, null);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onViewCreated(view, savedInstanceState);

    setListAdapter(new ArrayAdapter<String>(getSherlockActivity(), android.R.layout.simple_list_item_multiple_choice, android.R.id.text1, bandList));
    }
}

I am still learning to code in this environment, so I guess this is just some beginner mistake?

EDIT: (it’s a bit much but you asked)

public class BandDatabaseAdapter {

 private static final String TAG = "BandDatabase";

 private static final String BANDDATABASE_NAME = "BAND_DATABASE";
 private static final String BANDDATABASE_TABLE = "BAND_TABLE";
 private static final int BANDDATABASE_VERSION = 1;
 public static final String BAND_NAME = "name";
 public static final String BAND_GENRE = "genre";
 public static final String BAND_POPULAR = "popular";
 public static final String BAND_SELECTED = "selected";

 private static final String BANDDATABASE_CREATE="CREATE TABLE IF NOT EXISTS " + BANDDATABASE_TABLE
 + " (_id integer primary key autoincrement, " + BAND_NAME
 + " TEXT NOT NULL, " + BAND_GENRE + " TEXT NOT NULL, " + BAND_POPULAR
 + " TEXT NOT NULL, " + BAND_SELECTED + " TEXT NOT NULL)";

 private SQLiteHelper sqLiteHelper;
 private SQLiteDatabase sqLiteDatabase;
 private final Context context;

 public BandDatabaseAdapter(Context c) {
       sqLiteHelper = new SQLiteHelper(c, BANDDATABASE_NAME, null, BANDDATABASE_VERSION);
       context = c;
    }

 public BandDatabaseAdapter openToRead() throws android.database.SQLException {
  sqLiteDatabase = sqLiteHelper.getReadableDatabase();
  return this; 
 }

 public BandDatabaseAdapter openToWrite() throws android.database.SQLException {
  sqLiteDatabase = sqLiteHelper.getWritableDatabase();
  return this; 
 }

 public void close(){
  sqLiteHelper.close();
 }

 public void updateBand(String name, String selected) {
     ContentValues contentValues = new ContentValues();
     contentValues.put(BAND_SELECTED, selected);
     sqLiteDatabase.update(BANDDATABASE_TABLE, contentValues, "BAND_NAME=" + name, null);
     close();
 }

 public List<String> getAllRockBands() {
     List<String> bandList = new ArrayList<String>();

     String selection = BAND_GENRE + "=1";

     SQLiteDatabase db = sqLiteHelper.getReadableDatabase();
     Cursor cursor = db.query(BANDDATABASE_TABLE,new String[]{BAND_NAME}, selection, null, null, null, BAND_NAME);

     if(cursor!=null)
     {
     int index = cursor.getColumnIndex(BAND_NAME);

     if (cursor.moveToFirst()) {
         do {
          String bandName = cursor.getString(index);
             bandList.add(bandName);
         } while (cursor.moveToNext());
     }
     }
     return bandList;
 }

 public List<String> getMyList() {
     List<String> myList = new ArrayList<String>();

     String selection = BAND_SELECTED + "=1";

     SQLiteDatabase db = sqLiteHelper.getReadableDatabase();
     Cursor cursor = db.query(BANDDATABASE_TABLE,new String[]{BAND_NAME}, selection, null, null, null, BAND_NAME);

     int index = cursor.getColumnIndex(BAND_NAME);

     if (cursor.moveToFirst()) {
         do {
          String bandName = cursor.getString(index);
             myList.add(bandName);
         } while (cursor.moveToNext());
     }

     return myList;
 }

 public class SQLiteHelper extends SQLiteOpenHelper {

  public SQLiteHelper(Context context, String name,
    CursorFactory factory, int version) {
   super(context, name, factory, version);
  }

  private boolean doesDatabaseExist(Context context, String dbName) {
        File dbFile=context.getDatabasePath(dbName);
        return dbFile.exists();
    }

  @Override
  public void onCreate(SQLiteDatabase db) {
   // TODO Auto-generated method stub
   if(!(doesDatabaseExist(context,BANDDATABASE_NAME)))
   {
      db.execSQL(BANDDATABASE_CREATE);
      loadDatabase();
   }
  }

  /**
   * Starts a thread to load the database table with bands
   */
  private void loadDatabase() {
      new Thread(new Runnable() {
          public void run() {
              try {
                  loadBands();
              } catch (IOException e) {
                  throw new RuntimeException(e);
              }
          }
      }).start();
  }

  //loads a database from a txt file
  private void loadBands() throws IOException {
      Log.d(TAG, "Loading bands...");
      final Resources resources = context.getResources();
      InputStream inputStream = resources.openRawResource(R.raw.bands);
      BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

      try {
          String line;
          while ((line = reader.readLine()) != null) {
              String[] strings = TextUtils.split(line, "^");
              if (strings.length < 4) continue;
              long id = addBand(strings[0].trim(), strings[1].trim(), strings[2].trim());
              if (id < 0) {
                  Log.e(TAG, "unable to add band: " + strings[0].trim());
              }
          }
      } finally {
          reader.close();
      }
      Log.d(TAG, "DONE loading words.");
  }

  public long addBand(String name, String genre, String popular) {
      ContentValues initialValues = new ContentValues();
      initialValues.put(BAND_NAME, name);
      initialValues.put(BAND_GENRE, genre);
      initialValues.put(BAND_POPULAR, popular);
      initialValues.put(BAND_SELECTED, "0");

      return sqLiteDatabase.insert(BANDDATABASE_TABLE, null, initialValues);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
   // TODO Auto-generated method stub
    // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + BANDDATABASE_TABLE);

        // Create tables again
        onCreate(db);
  }

 }

}

Additional info: Some people have told me to use SimpleCursorAdapter, but it says it is deprecated. Also, note that my list has over 150k rows, tho I will greatly lessen that if the need arises. 🙂

Answer 1

It looks like you haven’t created SqliteHelper Class object before calling getAllRockBands() Please check that once or else post your SqliteHelper Class Constructor code

Changing your code here check it.

public class RockAllFragment extends SherlockListFragment {

    private BandDatabaseAdapter mySQLiteAdapter;
    private List<String> bandList;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    return inflater.inflate(R.layout.my_list, null);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onViewCreated(view, savedInstanceState);
    mySQLiteAdapter= new BandDatabaseAdapter(getSherlockActivity());
    bandList  = mySQLiteAdapter.getAllRockBands();

    setListAdapter(new ArrayAdapter<String>(getSherlockActivity(), android.R.layout.simple_list_item_multiple_choice, android.R.id.text1, bandList));
    }
}

you got NullPointerException because you have declared BandDatabaseAdapter but not created its instance. you need create its instance and then call it. in the above code I have created the object first and then called. Hope it helps you.