NullPointerException void io.realm.RealmChangeListener.onCha

Question

我正试图在我的项目中实现Realm数据库，我有一个带有在数据库中添加项的方法的类，我使用该类来存储这些方法并在我的片段中调用它们，但当我这样做时，我会得到一个错误：

java.lang.NullPointerException: Attempt to invoke interface method 'void io.realm.RealmChangeListener.onChange()' on a null object reference

我在这里做错了什么？

public class Repositorio extends GlobalActivity {

    private RealmChangeListener realmListener;
    public Realm realm;
    private Context context;

    public Repositorio() {
    }
    public Repositorio(Context context) {
        this.context = context;
        this.realm = Realm.getDefaultInstance();
        this.realmListener = new RealmChangeListener() {
            @Override
            public void onChange() {
                Log.i("realmtest", "some values in the database have been changed");
            }
        };
        this.realm.addChangeListener(realmListener);
    }

    public void addCliente(String nome, String local, String estado, String telefone, String email, String tipo) {
        realm.beginTransaction();
        Pessoa mPessoa = realm.createObject(Pessoa.class);
        mPessoa.setId(UUID.randomUUID().toString());
        mPessoa.setNome(nome);
        mPessoa.setCidade(local);
        mPessoa.setEstado(estado);
        mPessoa.setTelefone(telefone);
        mPessoa.setEmail(email);
        mPessoa.setTipo(tipo);
        realm.commitTransaction();

        Toast.makeText(context, "Cliente adicionado com sucesso", Toast.LENGTH_LONG).show();
    }
    @Override
    public void onPause() {
        super.onPause();
        realm.removeChangeListener(realmListener);
    }
    @Override
    public void onResume() {
        super.onResume();
        realm.addChangeListener(realmListener);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (realm != null) {
            realm.close();
            realm = null;
        }
    }

}

片段：

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        final View v = inflater.inflate(R.layout.cadastra_produtos, container, false);
        mRepositorio = new Repositorio(getActivity());
        novocliente = (TextView) v.findViewById(R.id.novocliente);

        novocliente.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mRepositorio.addCliente("ZÉ", "LALAAL", "SC", "3333-3333", "[e-mail]", "Pessoa Física");
            }
        });
        return v;
    }

全球：

public class GlobalActivity extends AppCompatActivity {
    public Ferramentas mFerramentas;
    public Realm realm;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mFerramentas = new Ferramentas();
        realm = Realm.getDefaultInstance();

    }

}

Answer 1

Android框架使用默认构造函数（公共且无参数）实例化Repositorio活动。

Repositorio的默认构造函数不将Listener实例分配给realmListener字段。

因此，当调用onResume()时，realm.addChangeListener(realmListener);等效于realm.addChangeListener(null);。

您不应该定义默认构造函数以外的构造函数。此外，您不应该手动实例化"活动"（Repositoryio）。