java - 为什么使用 Retrofit2 无法得到响应？

Question

我之前没怎么用过retrofit。但在这个项目中我将使用改造。当尝试从服务器获取响应时，无法得到响应。它会出现此错误:

java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 2 path $

这里有什么问题吗？

这是我的 postman 结果:

ApiInterface.java

public interface ApiInterface {
    @GET("/categories/0")
    Call<Category> getCategoryList();
}

ApiClient.java

public class ApiClient {

    private static Retrofit retrofit;
    private static final String BASE_URL = MyConstants.URL;

    public static Retrofit getRetrofitInstance() {

        if (retrofit == null) {
            retrofit = new retrofit2.Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }

CategoryFragment.java

public class CategoriesFragment extends Fragment {

    RecyclerView mRecyclerView;
    List<Category> categoryList;
    Category category;

    public CategoriesFragment() {
        // Required empty public constructor
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);

        }

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_categories, container, false);
        mRecyclerView = view.findViewById(R.id.recyclerview);
        GridLayoutManager mGridLayoutManager = new GridLayoutManager(getActivity(), 2);
        mRecyclerView.setLayoutManager(mGridLayoutManager);

        ApiInterface apiInterface = ApiClient.getRetrofitInstance().create(ApiInterface.class);
        Call<Category> call = apiInterface.getCategoryList();
        call.enqueue(new Callback<Category>() {
            @Override
            public void onResponse(Call<Category> call, Response<Category> response) {
                if (response.isSuccessful()) {
                    Category category_list = response.body();
                    Log.d("cateogry", "");
                    // CategoryAdapter myAdapter = new CategoryAdapter(getActivity(), categoryList);
                    //      mRecyclerView.setAdapter(new CategoryAdapter(category, R.layout.category_item_view, ));
                    // mRecyclerView.setAdapter(myAdapter);
                }
                else
                  //  ApiErrorUtils.parseError(response);
                  Log.d("Api hata", "");
            }

            @Override
            public void onFailure(Call<Category> call, Throwable t) {
                Log.d("Error", t.getMessage());
            }
        });

        return view;
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
//            throw new RuntimeException(context.toString()
  //                  + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }


    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }
}

Answer 1

您的API预计回复Object但实际响应是Array 。您应该使用List<Category>而不是<Category> 。就像下面这样

public interface ApiInterface {

    @GET("/categories/0")
    Call<List<Category>> getCategoryList();
}

API 调用应如下所示。

Call<List<Category>> call = apiInterface.getCategoryList();
        call.enqueue(new Callback<List<Category>>() {
            @Override
            public void onResponse(Call<List<Category>> call, Response<List<Category>> response) {
                if (response.isSuccessful()) {
                    List<Category> category_list = response.body();
                    Log.d("cateogry",category_list.size());
                    // CategoryAdapter myAdapter = new CategoryAdapter(getActivity(), categoryList);
                    //      mRecyclerView.setAdapter(new CategoryAdapter(category, R.layout.category_item_view, ));
                    // mRecyclerView.setAdapter(myAdapter);
                }
                else
                  //  ApiErrorUtils.parseError(response);
                  Log.d("Api hata", "");
            }

            @Override
            public void onFailure(Call<List<Category>> call, Throwable t) {
                Log.d("Error", t.getMessage());
            }
        });