How to remove the error of working with the database?

Question

Android

application crashes. in the logs refers to the line SQLiteDatabase database = dbHelper.getWritableDatabase();

public class Cold extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {
        DBHelper dbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cold);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        SwipeMenuListView listView = (SwipeMenuListView) findViewById(R.id.listView);
        List<ListData> cold = new ArrayList<>();
        cold.add(new ListData("Филадельфия Classic ", 169, R.drawable.filadelfia));
        cold.add(new ListData("Радуга", 169, R.drawable.raduga));
        cold.add(new ListData("Двойной удар", 209, R.drawable.dvoi));
        cold.add(new ListData("Чикен хот", 209, R.drawable.chikenhot));
        cold.add(new ListData("Лава", 219, R.drawable.lava));
        cold.add(new ListData("Филадельфия премиум", 240, R.drawable.filadpro));
        cold.add(new ListData("Сливочный с лососем", 169, R.drawable.slivslos));
        cold.add(new ListData("Сайман", 240, R.drawable.saiman));
        cold.add(new ListData("Вегетарианский",149 , R.drawable.veg));
        cold.add(new ListData("Ясай ролл", 159, R.drawable.yasai));
        cold.add(new ListData("Калифорния", 169, R.drawable.california));
        cold.add(new ListData("Филадельфия в икре", 189, R.drawable.vikrefill));
        cold.add(new ListData("Чикен ролл", 209, R.drawable.chikenroll));
        cold.add(new ListData("Калифорния чиз", 209, R.drawable.californiachis));
        cold.add(new ListData("Калифорния с креветкой", 209, R.drawable.californiaskrev));
        cold.add(new ListData("Алькапоне", 210, R.drawable.alkap));
        cold.add(new ListData("Джаз блюз", 210, R.drawable.jazbluz));
        cold.add(new ListData("Чука", 210, R.drawable.chuka));
        cold.add(new ListData("Киота", 220, R.drawable.kiota));
        cold.add(new ListData("Дакота", 214, R.drawable.dakota));
        cold.add(new ListData("Вулкан", 219, R.drawable.vulkan));
        cold.add(new ListData("Спайси Эби", 220, R.drawable.spaisiebi));
        cold.add(new ListData("Вендетта", 230, R.drawable.vendeta));
        cold.add(new ListData("Окинава", 220, R.drawable.okinava));
        cold.add(new ListData("Угорь с грибам", 230, R.drawable.ugorsgribami));
        cold.add(new ListData("Ролл акори", 239, R.drawable.rollakori));
        cold.add(new ListData("Филадельфия роял", 240, R.drawable.fillroial));
        cold.add(new ListData("Крем чиз", 240, R.drawable.crem));
        cold.add(new ListData("Грин ролл", 179, R.drawable.green));
        cold.add(new ListData("Бонито", 189, R.drawable.bonito));
        cold.add(new ListData("Острый с тунцом", 199, R.drawable.ostristuncom));
        cold.add(new ListData("Цезарь маки", 209, R.drawable.cezarmakki));

final CustomArrayAdapter adapter = new CustomArrayAdapter(this, R.layout.item, cold);
        listView.setAdapter(adapter);
        SwipeMenuCreator creator = new SwipeMenuCreator() {

@Override
public void create(SwipeMenu menu) {
        //create an action that will be showed on swiping an item in the list
        SwipeMenuItem item1 = new SwipeMenuItem(
        getApplicationContext());
        item1.setBackground(new ColorDrawable(Color.DKGRAY));
        // set width of an option (px)
        item1.setWidth(dp2px(60));
        item1.setIcon(R.drawable.ic_action_corz);
        item1.setTitleSize(18);
        item1.setTitleColor(Color.WHITE);
        menu.addMenuItem(item1);

        SwipeMenuItem item2 = new SwipeMenuItem(
        getApplicationContext());
        // set item background
        item2.setBackground(new ColorDrawable(Color.RED));
        item2.setWidth(dp2px(60));
        item2.setIcon(R.drawable.ic_action_like);
        item2.setTitleSize(18);
        item2.setTitleColor(Color.WHITE);
        menu.addMenuItem(item2);

        SwipeMenuItem item3 = new SwipeMenuItem(
        getApplicationContext());
        // set item background
        item3.setBackground(new ColorDrawable(Color.YELLOW));
        item3.setWidth(dp2px(60));
        item3.setIcon(R.drawable.ic_action_like);
        item3.setTitleSize(18);
        item3.setTitleColor(Color.WHITE);
        menu.addMenuItem(item3);


        }
        };
        //set MenuCreator
        listView.setMenuCreator(creator);
        // set SwipeListener
        listView.setOnSwipeListener(new SwipeMenuListView.OnSwipeListener() {

@Override
public void onSwipeStart(int position) {
        // swipe start
        }

@Override
public void onSwipeEnd(int position) {
        // swipe end
        }
        });

        listView.setOnMenuItemClickListener(new SwipeMenuListView.OnMenuItemClickListener() {

@Override
public boolean onMenuItemClick(int position, SwipeMenu menu, int index) {

        String value3 = adapter.getItem(position).title;
        int value2 = adapter.getItem(position).price;
        final SQLiteDatabase database = dbHelper.getWritableDatabase();

        final ContentValues contentValues = new ContentValues();
        switch (index) {
        case 0:
        contentValues.put(DBHelper.KEY_NAME, value3);
        contentValues.put(DBHelper.KEY_PRICE, value2);


        database.insert(DBHelper.TABLE_IZBRANNOE, null, contentValues);;



        Toast.makeText(getApplicationContext(), "Action 2 for " + value3 +"__"+"цена"+"__"+ value2, Toast.LENGTH_SHORT ).show();

        break;

        case 1:
        Cursor cursor = database.query(DBHelper.TABLE_IZBRANNOE, null, null, null, null, null, null);

        if (cursor.moveToFirst()) {
        int idIndex = cursor.getColumnIndex(DBHelper.KEY_ID);
        int nameIndex = cursor.getColumnIndex(DBHelper.KEY_NAME);
        int priceIndex = cursor.getColumnIndex(DBHelper.KEY_PRICE);
        do {
        Log.d("mLog", "ID = " + cursor.getInt(idIndex) +
        ", name = " + cursor.getString(nameIndex) +
        ", price = " + cursor.getString(priceIndex));
        } while (cursor.moveToNext());
        } else
        Log.d("mLog","0 rows");

        cursor.close();
        break;
        case 2:
        database.delete(DBHelper.TABLE_IZBRANNOE, null, null);
        break;
        }
        return false;
        }
        });


        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
        this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        }

@Override
public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
        } else {
        super.onBackPressed();
        }
        }



@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camera) {
        // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
        }
        private int dp2px(int dp) {
                return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp,
                        getResources().getDisplayMetrics());
        }
        }

public class DBHelper  extends SQLiteOpenHelper{

    public static final int DATABASE_VERSION = 1;
    public static final String DATABASE_NAME = "contactDb";
    public static final String TABLE_IZBRANNOE = "contacts";

    public static final String KEY_ID = "_id";
    public static final String KEY_NAME = "name";
    public static final String KEY_PRICE= "price";

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table " + TABLE_IZBRANNOE + "(" + KEY_ID
                + " integer primary key on conflict replace," + KEY_NAME + " text unique on conflict ignore," + KEY_PRICE + " text" + ")");

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists " + TABLE_IZBRANNOE);

        onCreate(db);

    }
}

Answer 1

You have not initialized Helper. Here are my methods:

// открыть подключение
public void open() {
    mDBHelper = new DBHelper(mCtx, DB_NAME, null, DB_VERSION);
    mDB = mDBHelper.getWritableDatabase();
}

public boolean isOpen() {
    return mDB.isOpen();
}

// закрыть подключение
public void close() {
    if (mDBHelper != null)
        mDBHelper.close();
}