android 每次按下后退按钮时重新加载片段（onCreate）

Question

我是 android 的新手，在我的项目中使用片段。第一次创建我的片段然后调用 api 并在片段中加载数据。在这里，当我单击任何项目时，我用另一个片段替换了片段，还有另一个 api 调用并将数据加载到片段。现在这里为我生成了问题情况。从这里我返回 Button pressed.

片段重新加载与第一次创建相同，但它应该显示我在进入下一个片段之前离开时的数据。

所以请为我提供解决方案，如何获得与我离开时相同的数据意味着保存的实例状态数据。

我是我的第一个片段 getCategory 方法调用 Api 并第一次获取数据当我选择任何类别时我用另一个片段替换片段但是当我返回相同的 getCategory 方法时调用执行与第一次相同的过程。

片段不应在反压时再次调用 api 方法，它应该显示我之前点击过的相同类别。

我的第一个片段调用 api......

public class LandingFragment extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
     private String mParam1;
     private String mParam2;

     private GridLayoutManager gridLayoutManager;
     private static RecyclerView category_Grid;
     private Fragment myFragment = null;
     ProgressBar mProgressView;
     View mLoginFormView;
     private Category category;
     private CategoryAdapter categoryAdapter;
     private List<CategoryObject> rowListItem;
     private String productId;
     private OnFragmentInteractionListener mListener;

    public LandingFragment() {
       // Required empty public constructor
    }

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
      *
      * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment LandingFragment.
     */
     // TODO: Rename and change types and number of parameters
     public static LandingFragment newInstance(String param1, String param2)    {
        LandingFragment fragment = new LandingFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
     }

    @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 v= inflater.inflate(R.layout.fragment_landing, container, false);
        return v;
    }

     @Override
     public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

         initViews(view);
         RecyclerViewListeners();
     }

    // 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(Activity 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;
    }

    /**
      * This interface must be implemented by activities that contain this
      * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p/>
     * See the Android Training lesson <a href=
     *     "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
     }

    private void initViews(final View v) {
        mLoginFormView = (View)v.findViewById(R.id.mainView);
        mProgressView = (ProgressBar)v.findViewById(R.id.login_progress);
        category_Grid = (RecyclerView)v.findViewById(R.id.cat_grid);
        category_Grid.setHasFixedSize(true);
        gridLayoutManager = new GridLayoutManager(getActivity(), 3);
        category_Grid.setLayoutManager(gridLayoutManager);
     }

 private void RecyclerViewListeners(){
    category_Grid.addOnItemTouchListener(new    RecyclerTouchListener(getActivity(), category_Grid, new ItemClickListener(){
        @Override
        public void onClick(View view, int position) {

            String entityId = rowListItem.get(position).getCategoryId();
            String catName = rowListItem.get(position).getName();
            Integer ishave = rowListItem.get(position).getIshaveSubcategories();
            if(ishave==1) {
                myFragment = SubcategoryFragment.newInstance(""+catName, "" + entityId);
                ActivityUtils.launchFragementWithAnimation(myFragment, getActivity());
            }else{
                myFragment = ProductListFragment.newInstance("", "" + entityId);
                ActivityUtils.launchFragementWithAnimation(myFragment, getActivity());
            }
        }

        @Override
        public void onLongClick(View view, int position) {

        }
    }));
}

public void getCategory() {
    showProgress(true);
    String URL = getResources().getString(R.string.category_api);
    StringRequest req = new StringRequest(Request.Method.POST,URL, new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            VolleyLog.v("Response:%n %s", response);
            Gson gson = new GsonBuilder().serializeNulls().create();
            try {
                JSONObject jsonObject = new JSONObject(response);
                if (jsonObject.getString("status").equals(getResources().getString(R.string.response_success))){
                    category = gson.fromJson(response, Category.class);
                    rowListItem = category.getCategory();
                    if(navigationUpdated){
                        someEventListener.someEvent(rowListItem);
                        navigationUpdated = false;
                    }
                    Log.d("CATEGORYID::::::::",""+rowListItem.get(1).getCategoryId());
                    categoryAdapter = new CategoryAdapter(getActivity(),rowListItem);
                    category_Grid.setAdapter(categoryAdapter);
                    categoryAdapter.notifyDataSetChanged();


                    return;
                }
                else if (jsonObject.getString("status").equals(getResources().getString(R.string.login_Er_respose))){
                    Log.e("","ERRORRRRRR");
                    return;
                }
            } catch (JSONException e) {
                showProgress(false);
                Log.e("My App", "Could not parse malformed JSON: \"" + response + "\"");
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
              showProgress(false);
              VolleyLog.e("Error: ", error.getMessage());
        }
    }){
        @Override
        protected Map<String,String> getParams(){
            Map<String,String> params = new HashMap<String, String>();
            return params;
        }

        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            Map<String,String> params = new HashMap<String, String>();
            params.put("Content-Type","application/x-www-form-urlencoded");
            return params;
        }
    };
    AppController.getInstance().addToRequestQueue(req);
}

    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
    private void showProgress(final boolean show) {

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
        int shortAnimTime =   getResources().getInteger(android.R.integer.config_shortAnimTime);

        mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
        mLoginFormView.animate().setDuration(shortAnimTime).alpha(
                show ? 0 : 1).setListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
            }
        });

        mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
        mProgressView.animate().setDuration(shortAnimTime).alpha(
                show ? 1 : 0).setListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
            }
        });
    } else {

        mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
        mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
    }
}

Answer 1

您可以检查您的 rowListItem.size()，如果它的大小为 0，则调用 getCategory() 服务，否则从您的 rowListItem 加载数据。这是我用来从 arraylist 加载数据的示例代码，如果它不为空：

if (mArrayArticle.size() == 0) {
    isDataLoading = true;
    mRecyclerList.setVisibility(View.INVISIBLE);
    getCategory();
} else {
    mHomeItemAdapter = new HomeItemAdapter(getActivity(), mArrayArticle, this);
    mRecyclerList.setAdapter(mHomeItemAdapter);
}

这里mArrayArticle是我的ArrayList，希望对你有帮助

Answer 2

我想告诉你更多的说明.. 我如何实施@Bhvk_AndroidBee 解决方案

fragment backpressed call onActivityCreated 方法首先 overridefragment 中的这个方法

  @Override
    public void onActivityCreated(Bundle savedInstanceState) {
       super.onActivityCreated(savedInstanceState);

      //here you can check null condition for rowListItem
    }
}

在 onActivityCreated 方法中我检查了这样的条件

    @Override
     public void onActivityCreated(Bundle savedInstanceState) {
       super.onActivityCreated(savedInstanceState);
        if(rowListItem!=null){

           categoryAdapter = new CategoryAdapter(getActivity(),rowListItem);
           category_Grid.setAdapter(categoryAdapter);
           categoryAdapter.notifyDataSetChanged();

       }else {

        //call the method for first time creating your view

           getCategory();

       }
    }

希望这对更多像我这样的奋斗者有所帮助...

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