public class DbHelper extends SQLiteOpenHelper {
public static final String TAG = DbHelper.class.getSimpleName();
public static final String DB_NAME = "myapp.db";
public static final int DB_VERSION = 1;

public static final String USER_TABLE = "users";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_usurarios = "usurarios";
public static final String COLUMN_PASS = "password";

/*
create table users(
    id integer primary key autoincrement,
    usurarios text,
    password text);
 */
public static final String CREATE_TABLE_USERS = "CREATE TABLE " + USER_TABLE + "("
        + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
        + COLUMN_usurarios + " TEXT,"
        + COLUMN_PASS + " TEXT);";

public DbHelper(Context applicationContext, Object o, Context context, int i) {
    super(context, DB_NAME, null, DB_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(CREATE_TABLE_USERS);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + USER_TABLE);
    onCreate(db);
}

/**
 * Storing user details in database
 * */
public void addUser(String usurarios, String password) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(COLUMN_usurarios, usurarios);
    values.put(COLUMN_PASS, password);

    long id = db.insert(USER_TABLE, null, values);
    db.close();

    Log.d(TAG, "Usuario insertado" + id);
}





public boolean getUser(String usurarios, String pass){
    //HashMap<String, String> user = new HashMap<String, String>();
    String selectQuery = "select * from  " + USER_TABLE + " where " +
            COLUMN_usurarios + " = " + "'"+usurarios+"'" + " and " + COLUMN_PASS + " = " + "'"+pass+"'";

    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);
    // Move to first row
    cursor.moveToFirst();
    if (cursor.getCount() > 0) {

        return true;
    }
    cursor.close();
    db.close();

    return false;
}

public String eliminar(String usuarios){
    String mensaje="";

    SQLiteDatabase db= this.getWritableDatabase();

    int cantidad = db.delete(USER_TABLE,"usuarios=?",new String[]{usuarios});

    if(cantidad!=0){
        mensaje="eliminado correctamente";
    }else{
        mensaje="No existe";
    }

    return mensaje;
}
public ArrayList llenar_lv(){
    ArrayList<String> lista = new ArrayList<>();
    SQLiteDatabase database = this.getWritableDatabase();
    String q = "SELECT * FROM datos";
    Cursor registros = database.rawQuery(q,null);
    if(registros.moveToFirst()){
        do{
            lista.add(registros.getString(1));
        }while(registros.moveToNext());
    }
    return lista;

}

public class RegisterActivity extends AppCompatActivity implements View.OnClickListener{
private Button reg,eliminar;
private TextView tvLogin;
private EditText etuser, etPass;

private DbHelper db;







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

    db = new DbHelper(getApplicationContext(), null, this, 1);
    reg = (Button)findViewById(R.id.btnReg);
    eliminar=(Button)findViewById(R.id.button);
    tvLogin = (TextView)findViewById(R.id.tvLogin);

    etuser = (EditText)findViewById(R.id.etuser);
    etPass = (EditText)findViewById(R.id.etPass);
    reg.setOnClickListener(this);
    tvLogin.setOnClickListener(this);

    eliminar.setOnClickListener(new  View.OnClickListener(){


        @Override
        public void onClick(View v){
            DbHelper db = new  DbHelper(getApplicationContext(),null,null,1);
            String usuarios = etuser.getText().toString();
            String mensaje = db.eliminar(usuarios);
            Toast.makeText(getApplicationContext(),mensaje,Toast.LENGTH_SHORT).show();


        }
    });
}



@Override
public void onClick(View v) {
    switch(v.getId()){
        case R.id.btnReg:
            register();
            break;
        case R.id.tvLogin:
            startActivity(new Intent(RegisterActivity.this,LoginActivity.class));
            finish();
            break;
        default:

    }
}






private void register(){
    String user = etuser.getText().toString();
    String pass = etPass.getText().toString();
    if(user.isEmpty() && pass.isEmpty()){
        displayToast("Usuario o contraseña vacio");
    }else{
        db.addUser(user,pass);
        displayToast("Usuario registrado con exito!");
        finish();
    }
}







private void displayToast(String message){
    Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT).show();
}