java - 当我从下一个选项卡返回时，我丢失了我的查看寻呼机数据

Question

我的 View pager 中有四个选项卡 我在 google 中进行了搜索，但是当我滑动我的 view pager 时我找不到任何解决方案，它工作正常，就像 1-2-3-4 但是当我尝试滑动时反向 4-3-2-1 比我的数据丢失或者你可以说我的适配器丢失。我的 View 寻呼机在 Activity 中。当我转到下一页时我的数据丢失，然后返回我的数据丢失。 我的主要 Activity 是:

public class MainActivity extends AppCompatActivity {
    public static int notificationCountCart = 0;
    Toolbar toolbar;
    ActionBar actionBar;
    static ViewPager viewPager;
    static TabLayout tabLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        if (toolbar != null)
            setSupportActionBar(toolbar);
        actionBar = getSupportActionBar();
        if (actionBar != null) {

            TextView textView = new TextView(this);
            textView.setText("Shopping");
            textView.setTextSize(20);
            textView.setTypeface(null, Typeface.BOLD);
            textView.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT));
            textView.setGravity(Gravity.CENTER);
            textView.setTextColor(getResources().getColor(R.color.white));
            getSupportActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
            getSupportActionBar().setCustomView(textView);
            actionBar.setDisplayShowTitleEnabled(false);
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setHomeAsUpIndicator(new IconDrawable(this, FontAwesomeIcons.fa_angle_left).colorRes(R.color.white).actionBarSize());

        }
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

        viewPager = (ViewPager) findViewById(R.id.viewpagerrr);
        tabLayout = (TabLayout) findViewById(R.id.tabs);


        setupViewPager(viewPager);
        tabLayout.setupWithViewPager(viewPager);


    }

    @Override
    protected void onResume() {
        super.onResume();
        invalidateOptionsMenu();
    }


    @Override
    public void onBackPressed() {
        super.onBackPressed();

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // Get the notifications MenuItem and
        // its LayerDrawable (layer-list)
        MenuItem item = menu.findItem(R.id.action_cart);
        NotificationCountSetClass.setAddToCart(MainActivity.this, item, notificationCountCart);
        // force the ActionBar to relayout its MenuItems.
        // onCreateOptionsMenu(Menu) will be called again.
        invalidateOptionsMenu();
        return super.onPrepareOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_search) {
            startActivity(new Intent(MainActivity.this, SearchResultActivity.class));
            return true;
        } else if (id == R.id.action_cart) {

           /* NotificationCountSetClass.setAddToCart(MainActivity.this, item, notificationCount);
            invalidateOptionsMenu();*/
            startActivity(new Intent(MainActivity.this, CartListActivity.class));

           /* notificationCount=0;//clear notification count
            invalidateOptionsMenu();*/
            return true;
        } else if (id == android.R.id.home) {
            Intent intent = new Intent(MainActivity.this, HomeActivity.class);
            startActivity(intent);
            //  startActivity(new Intent(MainActivity.this, EmptyActivity.class));

        }
        return super.onOptionsItemSelected(item);
    }

    private void setupViewPager(ViewPager viewPager) {
        Adapter adapter = new Adapter(getSupportFragmentManager());
        ImageListFragment fragment = new ImageListFragment();
        SpeakerFragment speakerFragment = new SpeakerFragment();
        adapter.addFragment(fragment, getString(R.string.item_2));
        adapter.addFragment(speakerFragment, getString(R.string.item_4));
        adapter.addFragment(new HeadPhone(), getString(R.string.item_3));
        adapter.addFragment(new Offer(), getString(R.string.item_1));
        viewPager.setAdapter(adapter);
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }


    static class Adapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragments = new ArrayList<>();
        private final List<String> mFragmentTitles = new ArrayList<>();

        public Adapter(FragmentManager fm) {
            super(fm);
        }

        public void addFragment(Fragment fragment, String title) {
            mFragments.add(fragment);
            mFragmentTitles.add(title);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragments.get(position);
        }

        @Override
        public int getCount() {
            return mFragments.size();
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitles.get(position);
        }
    }
}

我的 fragment 是

    public class ImageListFragment extends Fragment {
    String category_Name, Category_ID, Product_ID, Product_Name, 
    Product_Image, Product_Price, Product_Sale, Cart;

    public static final String STRING_IMAGE_URI = "ImageUri";
    public static final String STRING_IMAGE_POSITION = "ImagePosition";
    private static MainActivity mActivity;
    ArrayList<SingleItemModel> singleItemModels;
    RecyclerView recyclerView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getCategoryone();
        Fresco.initialize(getContext());
        mActivity = (MainActivity) getActivity();

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        recyclerView = (RecyclerView) inflater.inflate(R.layout.layout_recylerview_list, container, false);
        return recyclerView;
    }



    public static class SimpleStringRecyclerViewAdapter
            extends RecyclerView.Adapter<ImageListFragment.SimpleStringRecyclerViewAdapter.ViewHolder> {

        // private String[] mValues;
        private ArrayList<SingleItemModel> mValues;
        private RecyclerView mRecyclerView;

        public static class ViewHolder extends RecyclerView.ViewHolder {
            public final View mView;
            public final SimpleDraweeView mImageView;
            public final LinearLayout mLayoutItem;
            public final ImageView mImageViewWishlist;
            TextView iTemName, itemDescription, itemPrice;

            public ViewHolder(View view) {
                super(view);
                mView = view;
                mImageView = (SimpleDraweeView) view.findViewById(R.id.image1);
                mLayoutItem = (LinearLayout) view.findViewById(R.id.layout_item);
                mImageViewWishlist = (ImageView) view.findViewById(R.id.ic_wishlist);
                iTemName = (TextView) view.findViewById(R.id.itemName);
                itemDescription = (TextView) view.findViewById(R.id.itemDescription);
                itemPrice = (TextView) view.findViewById(R.id.itemPrice);
            }
        }

        public SimpleStringRecyclerViewAdapter(RecyclerView recyclerView, ArrayList<SingleItemModel> items) {
            mValues = items;
            mRecyclerView = recyclerView;
        }

        @Override
        public ImageListFragment.SimpleStringRecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
            return new ImageListFragment.SimpleStringRecyclerViewAdapter.ViewHolder(view);
        }

        @Override
        public void onViewRecycled(ImageListFragment.SimpleStringRecyclerViewAdapter.ViewHolder holder) {
            if (holder.mImageView.getController() != null) {
                holder.mImageView.getController().onDetach();
            }
            if (holder.mImageView.getTopLevelDrawable() != null) {
                holder.mImageView.getTopLevelDrawable().setCallback(null);
//
            }
        }

        @Override
        public void onBindViewHolder(final ImageListFragment.SimpleStringRecyclerViewAdapter.ViewHolder holder, final int position) {
            SingleItemModel singleItemModel = mValues.get(position);
            holder.iTemName.setText(singleItemModel.getCategory_Name());
            final Uri uri = Uri.parse(singleItemModel.getProduct_Image());
            holder.mImageView.setImageURI(uri);
            holder.itemPrice.setText(singleItemModel.getProduct_Price());
            holder.itemDescription.setText(singleItemModel.getProduct_Sale());
        }

        @Override
        public int getItemCount() {
            return mValues.size();
        }
    }

    public void getCategoryone() {

        final RequestQueue queue = Volley.newRequestQueue(getActivity());
        StringRequest stringRequest = new StringRequest(Request.Method.POST, "http://proaudiobrands.com/app/feature.php",
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        Log.i("shabina shopping  response", response);
                        try {
                            singleItemModels = new ArrayList<>();
                            JSONObject mainObj = new JSONObject(response);
                            Log.d("shabina ", response);
                            JSONArray Feature_product = mainObj.getJSONArray("Feature_product");

                            for (int i = 0; i < Feature_product.length(); i++) {

                                JSONObject Feature_Product = Feature_product.getJSONObject(i);
                                String Category_Namee = Feature_Product.getString("Category_Namee");
                                String Category_IDs = Feature_Product.getString("Category_IDs");
                                JSONArray Product_List = Feature_Product.getJSONArray("Product_List");


                                for (int j = 0; j < Product_List.length(); j++) {
                                    JSONObject Category_Name = Product_List.getJSONObject(j);
                                    if (Category_Name.getString("Category_Name").equals("Microphones")) {
                                        category_Name = Category_Name.getString("Category_Name");
                                        Category_ID = Category_Name.getString("Category_ID");
                                        Product_ID = Category_Name.getString("Product_ID");
                                        Product_Name = Category_Name.getString("Product_Name");
                                        Product_Image = Category_Name.getString("Product_Image");
                                        Product_Price = Category_Name.getString("Product_Price");
                                        Product_Sale = Category_Name.getString("Product_Sale");
                                        Cart = Category_Name.getString("Cart");

                                        Log.e("sushil Category_Name", category_Name + " " + Category_ID + " " + Product_ID + " " + Product_Name + " " + Product_Image + " " + Product_Price + " " + Product_Sale + " " + Cart);
                                        SingleItemModel singleItemModel1 = new SingleItemModel(category_Name, Category_ID, Product_ID, Product_Name, Product_Image, Product_Price, Product_Sale, Cart);
                                        singleItemModels.add(singleItemModel1);
                                    }
                                    StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
                                    recyclerView.setLayoutManager(layoutManager);
                                    recyclerView.setAdapter(new ImageListFragment.SimpleStringRecyclerViewAdapter(recyclerView, singleItemModels));

                                }
                            }

                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }


                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e("error", error.toString());

            }


        }) {

            @Override
            protected Map<String, String> getParams() throws AuthFailureError {
                Map<String, String> params = new HashMap<>();
                params.put("method", "feature");
                params.put("userId", "PRO1");


                return params;
            }
        };
        stringRequest.setRetryPolicy(new DefaultRetryPolicy(
                90000,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        queue.add(stringRequest);


    }

}

Answer 1

用下面的内容替换您的 MainActivity

public class MainActivity extends AppCompatActivity {
    public static int notificationCountCart = 0;
    Toolbar toolbar;
    ActionBar actionBar;
    static ViewPager viewPager;
    static TabLayout tabLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        if (toolbar != null)
            setSupportActionBar(toolbar);
        actionBar = getSupportActionBar();
        if (actionBar != null) {

            TextView textView = new TextView(this);
            textView.setText("Shopping");
            textView.setTextSize(20);
            textView.setTypeface(null, Typeface.BOLD);
            textView.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT));
            textView.setGravity(Gravity.CENTER);
            textView.setTextColor(getResources().getColor(R.color.white));
            getSupportActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
            getSupportActionBar().setCustomView(textView);
            actionBar.setDisplayShowTitleEnabled(false);
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setHomeAsUpIndicator(new IconDrawable(this, FontAwesomeIcons.fa_angle_left).colorRes(R.color.white).actionBarSize());

        }
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

        viewPager = (ViewPager) findViewById(R.id.viewpagerrr);
        viewPager.setOffscreenPageLimit(4);
        tabLayout = (TabLayout) findViewById(R.id.tabs);


        setupViewPager(viewPager);
        tabLayout.setupWithViewPager(viewPager);


    }

    @Override
    protected void onResume() {
        super.onResume();
        invalidateOptionsMenu();
    }


    @Override
    public void onBackPressed() {
        super.onBackPressed();

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // Get the notifications MenuItem and
        // its LayerDrawable (layer-list)
        MenuItem item = menu.findItem(R.id.action_cart);
        NotificationCountSetClass.setAddToCart(MainActivity.this, item, notificationCountCart);
        // force the ActionBar to relayout its MenuItems.
        // onCreateOptionsMenu(Menu) will be called again.
        invalidateOptionsMenu();
        return super.onPrepareOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_search) {
            startActivity(new Intent(MainActivity.this, SearchResultActivity.class));
            return true;
        } else if (id == R.id.action_cart) {

           /* NotificationCountSetClass.setAddToCart(MainActivity.this, item, notificationCount);
            invalidateOptionsMenu();*/
            startActivity(new Intent(MainActivity.this, CartListActivity.class));

           /* notificationCount=0;//clear notification count
            invalidateOptionsMenu();*/
            return true;
        } else if (id == android.R.id.home) {
            Intent intent = new Intent(MainActivity.this, HomeActivity.class);
            startActivity(intent);
            //  startActivity(new Intent(MainActivity.this, EmptyActivity.class));

        }
        return super.onOptionsItemSelected(item);
    }

    private void setupViewPager(ViewPager viewPager) {
        Adapter adapter = new Adapter(getSupportFragmentManager());
        ImageListFragment fragment = new ImageListFragment();
        SpeakerFragment speakerFragment = new SpeakerFragment();
        adapter.addFragment(fragment, getString(R.string.item_2));
        adapter.addFragment(speakerFragment, getString(R.string.item_4));
        adapter.addFragment(new HeadPhone(), getString(R.string.item_3));
        adapter.addFragment(new Offer(), getString(R.string.item_1));
        viewPager.setAdapter(adapter);
        viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }


    static class Adapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragments = new ArrayList<>();
        private final List<String> mFragmentTitles = new ArrayList<>();

        public Adapter(FragmentManager fm) {
            super(fm);
        }

        public void addFragment(Fragment fragment, String title) {
            mFragments.add(fragment);
            mFragmentTitles.add(title);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragments.get(position);
        }

        @Override
        public int getCount() {
            return mFragments.size();
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitles.get(position);
        }
    }
}