public void loginTheUser(){
    loginuser.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            etCategory =(EditText)findViewById(R.id.editTextCategory);
            etName =(EditText)findViewById(R.id.editTextUserName);
            etPassword =(EditText)findViewById(R.id.editTextUserPassword);
            String name = etName.getText().toString();
            String pass = etPassword.getText().toString();
            String cat = etCategory.getText().toString();

            cursor = db.rawQuery("SELECT * FROM " + DbHelper.TABLE_USER + "WHERE " + DbHelper.COL_USERNAME + "=? AND " + DbHelper.COL_USERPASS + "=?  AND " + DbHelper.COL_USERCAT + "=?", new String[]{name, pass, cat});
            if (cursor != null) {
                if (cursor.getCount() > 0) {
                    Toast.makeText(MainActivity.this, "Login Success", Toast.LENGTH_SHORT).show();

                } else {
                    Toast.makeText(MainActivity.this, "Login error", Toast.LENGTH_SHORT).show();
                }
            }

        }
    });

}

Button buttonLogin,loginuser;
EditText etName, etPassword, etCategory;
DbHelper dbHelper;
SQLiteDatabase db;
SQLiteOpenHelper openHelper;
Cursor cursor;

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

    openHelper=new DbHelper(this);
    db = openHelper.getReadableDatabase();
    //db = openHelper.getWritableDatabase();


    buttonLogin = (Button)findViewById(R.id.btnLogin);
    loginuser = (Button)findViewById(R.id.buttonlogging);
    //etCategory =(EditText)findViewById(R.id.editTextCategory);
    //etName =(EditText)findViewById(R.id.editTextUserName);
    //etPassword =(EditText)findViewById(R.id.editTextUserPassword);
    loginTheUser();






}