java - RecyclerView 并不总是加载 JSON 数据

Question

我正在学习编写 Android 应用程序。尝试解析 json 以将结果保存在 RecyclerView 中，在跨 Activity 或按主页按钮然后返回时，有时会加载这些结果，有时则不会加载。对于 http 调用，我使用 OkHttp。我尝试过其他解决方案，但没有一个解决方案解决了我的问题，即使由于我是初学者，我可能在操作逻辑上做错了什么。

public class VehiclesListFragment extends Fragment {  

...

private OkHttpClient httpClient = new OkHttpClient();
    final List<Vehicle> vehicles = new ArrayList<>();
    private String url = "myurl";
    final Request request = new Request.Builder().url(url).build();  

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.vehicles_recycler_view, container, false);

VehicleRecyclerView = (RecyclerView)view.findViewById(R.id.vehicles_recycler_view);
 VehicleRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

 VehicleRecyclerView.addItemDecoration(new DividerItemDecoration(getContext(),
                     DividerItemDecoration.VERTICAL));

        updateUI();

        return view;

    }  


private void updateUI() {

        httpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(@NotNull Call call, @NotNull IOException e) {
                Log.d("Error", "Error!");
            }
            @Override
            public void onResponse(@NotNull Call call, @NotNull final Response response) throws IOException {
                if(response.isSuccessful()){
                    final String body = response.body().string();

                        try {
                            JSONObject Jobject = new JSONObject(body);
                            JSONArray Jarray = Jobject.getJSONArray("models");
                            for (int i = 0; i < Jarray.length(); i++) {
                                Vehicle vehicle = new Vehicle();
                                JSONObject Jobj = Jarray.getJSONObject(i);
                                vehicle.setName(Jobj.getString("Name"));
                                vehicle.setBrand(Jobj.getString("Brand"));
                                plane.setYear(Jobj.getString("Year"));
                                vehicles.add(vehicle);
                            }
                        } catch (JSONException e) {e.printStackTrace();}
                }
            }
        });

        Adapter = new PlaneAdapter(planes);
        PlaneRecyclerView.setAdapter(Adapter);
        Adapter.notifyDataSetChanged();
}

RecyclerView 有时加载，有时不加载，特别是在跨 Activity 或按主页并恢复时。

我尝试移动适配器构造函数的位置以及设置和错误更改，但我不明白我缺少什么。如果您需要更多代码，我会提供。

谢谢。

Answer 1

您应该在回调中更新回收器 View 。

private void updateUI() {

    httpClient.newCall(request).enqueue(new Callback() {
        @Override
        public void onFailure(@NotNull Call call, @NotNull IOException e) {
            Log.d("Error", "Error!");
        }

        @Override
        public void onResponse(@NotNull Call call, @NotNull final Response response) throws IOException {
            if (response.isSuccessful()) {
                final String body = response.body().string();
                vehicles.clear();// Removes all of the elements
                try {
                    JSONObject Jobject = new JSONObject(body);
                    JSONArray Jarray = Jobject.getJSONArray("models");
                    for (int i = 0; i < Jarray.length(); i++) {
                        Vehicle vehicle = new Vehicle();
                        JSONObject Jobj = Jarray.getJSONObject(i);
                        vehicle.setName(Jobj.getString("Name"));
                        vehicle.setBrand(Jobj.getString("Brand"));
                        vehicle.setYear(Jobj.getString("Year"));
                        vehicles.add(vehicle);
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
                new Handler(Looper.getMainLooper()).post(new Runnable() {
                    @Override
                    public void run() {
                        if (null == Adapter) {
                            Adapter = new PlaneAdapter(vehicles);
                            PlaneRecyclerView.setAdapter(Adapter);
                        } else {
                            Adapter.notifyDataSetChanged();
                        }
                    }
                });
            }
        }
    });
}