java - 卡在 Android.os.Bundle 上且对象引用为空

Question

不知道为什么会出现这个错误。我已经检查了链接到此代码的所有代码，但仍然没有给出任何解决方案。

IDE 只是给出这样的错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'int android.os.Bundle.getInt(java.lang.String)' on a null object reference at com.gook.rebill.fragment.HomeFragment.onAttach(HomeFragment.java:74)

我知道这是一个空对象引用，但我仍然不知道错误原因在哪里。

请帮助我。

这是我的代码:

    public class HomeFragment extends Fragment implements InternetConnectionListener, ApiHandler.ApiHandlerListener {

    private static final String ARG_SECTION_NUMBER = "section_number";
    private final int CATEGORY_ACTION = 1;
    private CategorySelectionCallbacks mCallbacks;
    private ArrayList<Category> categoryList;
    private ListView categoryListView;
    private String Error = null;
    private InternetConnectionListener internetConnectionListener;

    public HomeFragment() {

    }

    public static HomeFragment newInstance(int sectionNumber) {
        HomeFragment fragment = new HomeFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((HomeActivity) activity).onSectionAttached(getArguments().getInt(ARG_SECTION_NUMBER));
        try {
            mCallbacks = (CategorySelectionCallbacks) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException("Activity must implement CategorySelectionCallbacks.");
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_home, container, false);
        categoryListView = (ListView) rootView.findViewById(R.id.categoryListView);
        return rootView;
    }

    @Override
    public void onResume() {
        super.onResume();
        if (UtilMethods.isConnectedToInternet(getActivity())) {
            initCategoryList();
        } else {
            internetConnectionListener = (InternetConnectionListener) HomeFragment.this;
            showNoInternetDialog(getActivity(), internetConnectionListener,
                    getResources().getString(R.string.no_internet),
                    getResources().getString(R.string.no_internet_text),
                    getResources().getString(R.string.retry_string),
                    getResources().getString(R.string.exit_string), CATEGORY_ACTION);
        }

    }

    public class getCategList extends AsyncTask<Void, Void, Void>{

        @Override
        protected Void doInBackground(Void... params) {

            /**
             * json is populating from text file. To make api call use ApiHandler class
             *
             *  <CODE>ApiHandler apiHandler = new ApiHandler(this, URL_GET_CATEGORY);</CODE> <BR>
             *  <CODE>apiHandler.doApiRequest(ApiHandler.REQUEST_GET);</CODE> <BR>
             *
             * You will get the response in onSuccessResponse(String tag, String jsonString) method
             * if successful api call has done. Do the parsing as the following.
             */
            URL hp = null;
            try {
                hp = new URL(
                        getString(R.string.liveurl) + "foodcategory.php");

                Log.d("URL", "" + hp);
                URLConnection hpCon = hp.openConnection();
                hpCon.connect();
                InputStream input = hpCon.getInputStream();

                BufferedReader r = new BufferedReader(new InputStreamReader(input));

                String x = "";
                x = r.readLine();
                String total = "";

                while (x != null) {
                    total += x;
                    x = r.readLine();
                }
                Log.d("UR1L", "" + total);

                JSONArray j = new JSONArray(total);

                Log.d("URL1", "" + j.length());



                categoryList = new ArrayList<Category>();

                for (int i = 0; i < j.length(); i++) {
                    Category category = new Category();// buat variabel category
                    JSONObject Obj;
                    Obj = j.getJSONObject(i); //sama sperti yang lama, cman ini lebih mempersingkat karena getJSONObject cm d tulis sekali aja disini

                    category.setId(Obj.getString(JF_ID));
                    category.setTitle(Obj.getString(JF_TITLE));
                    category.setIconUrl(Obj.getString(JF_ICON));

                    if (!TextUtils.isEmpty(Obj.getString(JF_BACKGROUND_IMAGE))) {
                        category.setImageUrl(Obj.getString(JF_BACKGROUND_IMAGE));
                    }
                    Log.d("URL1",""+Obj.getString(JF_TITLE));
                    categoryList.add(category);
                }

                getActivity().runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        categoryListView.setAdapter(new CategoryAdapter(getActivity(), mCallbacks, categoryList));
                    }
                });



            }catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                Error = e.getMessage();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                Error = e.getMessage();
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                Error = e.getMessage();
                e.printStackTrace();
            } catch (NullPointerException e) {
                // TODO: handle exception
                Error = e.getMessage();
            }
            return null;
        }
    }



    //! function for populate category list
    private void initCategoryList() {
            new getCategList().execute();
    }

    @Override
    public void onConnectionEstablished(int code) {
        if (code == CATEGORY_ACTION) {
            initCategoryList();
        }
    }

    @Override
    public void onUserCanceled(int code) {
        if (code == CATEGORY_ACTION) {
            getActivity().finish();
        }
    }

    //! catch json response from here
    @Override
    public void onSuccessResponse(String tag, String jsonString) {
        //! do same parsing as done in initCategoryList()
    }

    //! detect response error here
    @Override
    public void onFailureResponse(String tag) {

    }

    //! callback interface listen by HomeActivity to detect user click on category
    public static interface CategorySelectionCallbacks {
        void onCategorySelected(String catID, String title);
    }
}

这里我在 HomeActivity 中使用 fragment 代码:

 public void onSectionAttached(int number) {
    switch (number) {
        case 1:
            mTitle = getString(R.string.title_section1);
            break;
        case 2:
            mTitle = getString(R.string.title_section2);
            break;
        case 3:
            mTitle = getString(R.string.title_section3);
            break;
    }
}

Answer 1

我认为 getArguments() 返回 null。
您可以看到这些示例:
Android Fragment getArguments() returns null
Fragment getArguments() returns null