java - 即使在对象已初始化后仍为空对象引用

Question

我正在尝试尽最大努力为我正在尝试创建的这个特定项目使用 fragment 。我正在我创建的 fragment 类中进行所有网络调用。当我调用建立连接的方法并将结果记录到控制台时，我从类中获取所有信息，但是当我尝试访问网络调用之外的实例时，我收到空指针异常。我一直在查看文档和其他示例，但其中大多数的做法与我需要的不同，并且文档没有提及在 fragment 内使用 okhttp 。

我正在使用的代码是这样的:

public void testAsyncCreate() {

        OkHttpClient client  = new OkHttpClient();


        RequestBody body = RequestBody.create(CREATE_MEDIA_TYPE, "data={\"process\":\"123\", \"phone\":\"111111111\"}");


        Request request = new Request.Builder()
                .url(ALLWAYS_API)
                .post(body)
                .build();

        Call call = client.newCall(request);

        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                // any additional runnable items go in here
                try {


                    String jsonData = response.body().string(); // the exception is caught at this point
                    Log.d("<Mensajes>",jsonData);
                    //extractCreate = parseExtractCreateDetails(jsonData);
                    if(response.isSuccessful()) {
                        extractCreate = parseExtractCreateDetails(jsonData);
                        getActivity().runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                Log.d("<=====>", "check");
                                Log.d(TAG, "Is this even working?");
                                Log.d("The class has been ok",extractCreate.getCreateR().getAccount_id().toString());
                                Log.d("Another check", extractCreate.getStopsR()[1].getAddress());



                            }
                        });
                    }

                    //getStops(jsonData);

                }catch(IOException e) {

                }catch (JSONException e){

                }


            }
        });
    } // end of asyncCreate

然后在 onCreateView() 方法中:

ExtractCreate extractCreate = new ExtractCreate();

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);
        View view = inflater.inflate(R.layout.fragments_stops_list, container, false);
        ButterKnife.bind(this, view);

        if (savedInstanceState == null) {
              testAsyncCreate();
        }
        Log.d("<extractCreateCheck>", String.valueOf(extractCreate.getCreateR().getAccount_id()));

        return view:
    }

我不明白为什么这在使用 fragment 时不起作用，我这么说的原因是因为如果我将其放入常规 Activity 中并运行它，我将能够在其他任何地方使用 extractCreate 的结果想要，但不在这里。关于在 fragment 内使用 okhttp 调用，我是否缺少任何步骤？这些文档目前对我来说没有任何意义。堆栈跟踪如下:

11-23 09:28:55.569 3288-3288/com.example.testC.demotrackertree E/AndroidRuntime: FATAL EXCEPTION: main                                                                                   
        Process: com.example.testC.demotrackertree, PID: 11142
        java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String at com.example.testC.demotrackertree.models.createmodels.CreateResponse.getAccount_id()' on a null object reference
        at com.example.testC.demotrackertree.ui.fragments.StopCreateFragment.onCreateView(StopCreateFragment.java:95)
        at android.app.Fragment.performCreateView(Fragment.java:2353)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:995)
        at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1171)
        at android.app.BackStackRecord.run(BackStackRecord.java:816)
        at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1578)
        at android.app.FragmentManagerImpl$1.run(FragmentManager.java:483)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

正如其中一个人所建议的，我在响应中做了我想做的事情，

if(response.isSuccessful()) {
                        extractCreate = parseExtractCreateDetails(jsonData);
                        getActivity().runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
//                                Log.d("<=====>", "check");
//                                Log.d(TAG, "Is this even working?");
//                                Log.d("The class has been ok",extractCreate.getCreateR().getAccount_id().toString());
//                                Log.d("Another check", extractCreate.getStopsR()[1].getAddress());
                                Parcelable[] parcelable = extractCreate.getStopsR();

                                commodities = Arrays.copyOf(parcelable, parcelable.length, Stops[].class);
                                //Log.d("Commodities size check", String.valueOf(commodities.length));


                                StopsAdapter adapter = new StopsAdapter(extractCreate.getStopsR());
                                mRecyclerView.setAdapter(adapter);
                                RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity()); // sketchy on this part
                                mRecyclerView.setLayoutManager(layoutManager);
                                mRecyclerView.setHasFixedSize(true);
                                Log.d(TAG, "This is being called from the onCreate method");
                                //();



                            }
                        });
                    }

                    //getStops(jsonData);

                }catch(IOException e) {

                }catch (JSONException e){

                }


            }

现在， View 的内容按照我在适配器中指定的方式进行相应更新(意味着适配器按我的预期运行)，但在回调完成堆栈跟踪打印之前不会添加适配器

11-23 12:05:40.628 7270-7270/com.example.testC.demotrackertree E/RecyclerView: No adapter attached; skipping layout

不仅如此，当我旋转屏幕时，saveInstanceState 也不会被保留。

Answer 1

当您执行 AsyncTask 时，该操作与 UI 线程同时在后台线程上运行。 Log语句紧接在execute语句之后，因此当Log语句执行时，AsyncTask还没有加载变量中的信息。