无法通过翻新从Web服务中获取数据

Question

[我正在尝试使用Retrofit和Gson加载由Web服务生成的JSON格式的一些非常简单的数据，并尝试实现MVVM架构，但是当获得null值时从ViewModel调用数据：我已经看过很多SO问题（或可能不是很多），但无法弄清楚我在哪里以及为什么遇到此问题。

所以，我有这个

JSON响应：这可能是这个：

{
    "ok": [
        {
            "id": 1,
            "username": "test1",
            "pass": "123",
            "reg_date": "2020-05-20 00:00:00"
        }
    ]
}

或此：

{
    "error": [
        {
            "message":"user doesn't exists"
        }
    ]
}

我已经为每种响应类型创建了对应的POJO，为简单起见，我将其省略。但是我也创建了一个通用的POJO来处理响应（感​​谢@CôngHải，）

** POJOGenericResponse.java *

public class POJOGenericResponse{
    @SerializedName("ok")
    private LiveData<ArrayList<POJOUsr>> user;
    @SerializedName("error")
    private LiveData<ArrayList<POJOError>> error;

    //Constructor and Getters...
}

JsonApi.java

public interface JsonApi {
    @GET("SelectAllUsr.php")
    Call<LiveData<POJOGenericResponse>> getGenericResponse();
}

我不知道如何根据其目的和名称约定来调用该类

RetrofitInstance.java

public class RetrofitInstance {
    private static String URL_BASE = "http://192.168.0.35/app_android/webservices/";
    private static Retrofit retrofit;
    private static Gson gson;

    public Retrofit getRetrofitInstance(){
        gson = new GsonBuilder().setLenient().create();
        if(retrofit == null){
            retrofit = new Retrofit.Builder()
                    .baseUrl(URL_BASE)
                    .addConverterFactory(GsonConverterFactory.create(gson))
                    .build();
        }
        return retrofit;
    }
}

LoginRepository.java

public class LoginRepository{
    private RetrofitInstance retrofitInstance;
    private JsonApi jsonApi;
    private LiveData<POJOGenericResponse> genericResponse;
    private Call<LiveData<POJOGenericResponse>> call;

    public LoginRepository() {
        retrofitInstance = new RetrofitInstance();
        jsonApi = retrofitInstance.getRetrofitInstance().create(JsonApi.class);
        call = jsonApi.getRespuestaGenerica();
    }

    //TODO: This should be done in another class??
    public LiveData<POJOGenericResponse> getGenericResponse() {
        call.clone().enqueue(new Callback<LiveData<POJOGenericResponse>>() {

            @Override
            public void onResponse(Call<LiveData<POJOGenericResponse>> call, Response<LiveData<POJOGenericResponse>> response) {
                if (response.isSuccessful()) {
                    genericResponse= response.body();
                } else {
                    //
                }
            }

            @Override
            public void onFailure(Call<LiveData<POJOGenericResponse>> call, Throwable t) {
                //
            }
        });
        return genericResponse;
    }
}

LoginViewModel.java

public class LoginViewModel extends AndroidViewModel {
    private RepositorioLogin loginRepository;
    private MutableLiveData<POJOGenericResponse> serverResponse;

    public ViewModelLogin(@NonNull Application application) {
        super(application);
        loginRepository = new RepositorioLogin();
        serverResponse = new MutableLiveData<>();
    }

    public void setServerResponse(){
        serverResponse.setValue(loginRepository.getGenericResponse().getValue());
    }

    public LiveData<POJORespuestaGenerica> getServerResponse(){
        return serverResponse;
    }
}

此处应显示数据

FragmentData.java

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_data, container, false);
        TextView exampleText = v.findViewById(R.id.tv_test);

        LoginViewModel loginViewModel = new ViewModelProvider(requireActivity()).get(LoginViewModel.class);
        loginViewModel.getServerResponse().observe(requireActivity(), new Observer<POJORespuestaGenerica>() {
            @Override
            public void onChanged(POJOGenericResponse pojoGenericResponse) {
                if (pojoGenericResponse.getUser() != null) {
                    exampleText.setText(pojoGenericResponse.getUser().getValue().get(0).getUsername());
                }
                if (pojoGenericResponse.getError() != null) {
                    exampleText.setText(pojoGenericResponse.getError().getValue().get(0).getMensaje());
                }
            }
        });

调试时，我得到的错误是

response =找不到本地变量'response'serverResponse.setValue（loginRepository.getGenericResponse（）。getValue（））; \ n = java.lang.NullPointerExceptionresponse =找不到局部变量'response'

单独描述问题，但无法解决。

此外，对于MVVM架构实施的任何建议也将不胜感激。

之前，非常感谢

Answer 1

看起来像是不正确的位-