Создание динамических вкладок на основе длины массива Json сервера во фрагменте

Question

Я хочу создать фрагмент, который динамически добавляется и удаляется вкладки на основе длины массива JSON.Но это покажет ошибку в методе getTabAt ().Пожалуйста, помогите мне.Заранее спасибо.Вот мой код:

MainActivity.java

class MainActivity extends AppCompatActivity{
@Override
public void onCreate(){

 productViewPager = findViewById(R.id.productPage_viewPager);
 unitTab = findViewById(R.id.recycler_tab_layout);
 productViewPager.addOnPageChangeenter code hereListener(new 
 ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, 
  int positionOffsetPixels) {
        }

        @Override
        public void onPageSelected(int position) {
            highLightCurrentTab(position);

            /*System.out.println(tabLayout.getTag().toString());*/

        }

        @Override
        public void onPageScrollStateChanged(int state) {
        }
    });

    productPageFragment = new ProductPageFragment();
    adapterProductPageFragment = new 
    AdapterProductPageFragment(getSupportFragmentManager(), this);
    new getQuantity().execute("");
  }

  class getQuantity extends AsyncTask<String, String, String> {

  String str = null;
  String splitCatagory = null;

  @Override
  protected void onPreExecute() {
      super.onPreExecute();      }

  @Override
  protected String doInBackground(String... strings) {

      splitCatagory = strings[0];
      String[] SpliCatagory = splitCatagory.split("%26");
      if (SpliCatagory.length > 1) {
          str = SpliCatagory[0] + "&" + SpliCatagory[1];

      } else {
          str = strings[0];
      }
      String data1 = "";
      OkHttpClient client = new OkHttpClient();
      String s = new String();

      orderid=" + strings[0];
      Request request1 = new Request.Builder()
              .url(data1)
              .get()
              .build();

      try {
          Response response = client.newCall(request1).execute();
          //s = response.body().string();
          s = "{\"individualProduct_details\": 

[{\ ​​"product_discount_range_per_tranch_2 \": \ "0.2 \", \ "total_product_quantity_for_deal \": \ "0.0 \", \ "product_discount_range_per_tranch_1 \": \ "0.1 \", \" product_inventory_details \ ": \" 40 \ ", \" product_key_features \ ": \" Без сахара 1 кг \ ", \" product_level_community_upper_cut_off \ ": \" 20 \ ", \" product_discount_range_per_tranch_3 \ ": \" 0.3\ ", \" product_mrp \ ": \" 70.0 \ ", \" tranch1_product_price \ ": \" 65.14 \ ", \" product_selling_quantity_community_tranch_1 \ ": \" 10 \ ", \" product_quantity \ ": \" 1 КГ \", \" product_selling_quantity_community_tranch_2 \ ": \" 15 \ ", \" product_selling_quantity_community_tranch_3 \ ": \" 20 \ ", \" product_sku \ ": \" Без сахара \ ", \" product_per_day_price_discount \ ": \" 0.2 ", \ "product_subcategory \": \ "Salt Sugar and Jaggery \", \ "product_id \": \ "51 \", \ "product_availability \": \ "Available \", \ "product_level_upper_cut_off \": \ "3 \", \" product_description \ ": \" Без сахара 1 кг \ ", \" tranch1_order_count \ ": 0, \" tranch2_order_count \ ": 0, \" product_demand_heatmap \ ": \" 1 \ ", \" product_per_quantity_percent_price_drop \ ": \" 0,1 \ "\ "tranch2_product_price \": \ "65,08 \", \ "product_selling_price \": \ "66,0 \", \ "product_purchase_price \": \ "60,0 \", \" product_deal_price \": \" 65,21 \ "\ "product_purchase_percent \": \ "30 \", \ "image_id \": \" 9,10,12,13,16,17,18,19,20,21,22 \", \" product_category \ ": \" Бакалея и скобы \ "}, \ n" + "\ n" + "{\" product_discount_range_per_tranch_2 \ ": \" 0.2 \ ", \" image_id \ ": \" \ ", \ "total_product_quantity_for_deal \": \ "0.0 \", \ "product_discount_range_per_tranch_1 \": \ "0.1 \", \ "product_inventory_details \": \ "10 \", \ "product_key_features \": \ "Без сахара 2,5 кг», \ "product_level_community_upper_cut_off \": \ "20 \", \ "product_discount_range_per_tranch_3 \": \ "0,3 \", \ "product_mrp \": \ "140,0 \", \ "tranch1_product_price \": \ "128,31 \",\ "product_selling_quantity_community_tranch_1 \": \ "10 \", \ "product_quantity \": \ "2.5 KG \", \ "product_selling_quantity_community_tranch_2 \": \ "15 \", \ "product_selling_quantity_community_tranch_3 \", "\", \ ":"product_sku \": \ "Sugar Free \", \ "product_per_day_price_discount \": \ "0.2 \", \ "product_subcategory \": \ "Salt Sugar and Jaggery \", \ "product_id \": \ "52 \", \ "product_availability \": \ "Available \", \ "product_level_upper_cut_off \": \ "2 \", \ "product_description \"": \" Без сахара 2,5 кг \ ", \" tranch1_order_count \ ": 0, \" tranch2_order_count \ ": 0, \" product_demand_heatmap \ ": \" 2 \ ", \" product_per_quantity_percent_price_drop \ ": \" 0.1 \ "\ "tranch2_product_price \": \ "128,18 \", \ "product_selling_price \": \ "130,0 \", \ "product_purchase_price \": \ "120,0 \", \ "product_deal_price \": \ "128,44 \", \"product_purchase_percent \": \ "55 \", \ "product_category \": \ "Бакалея и скобы \"}]} \ n ";Log.e («ПРОДУКТЫ ----», s);} catch (IOException e) {e.printStackTrace ();

      }

      return s;
  }
      protected void onPostExecute(String s) {
          super.onPostExecute(s);

      try {
          JSONObject object = new JSONObject(s);
          JSONArray array = 
   object.getJSONArray("individualProduct_details");

          arrayLength = array.length();
          prod_quantity=new String[array.length()];


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

              JSONObject item = array.getJSONObject(i);
              String product_sku = item.getString("product_sku");

              String product_quantity = item.getString("product_id");

              String product_id = item.getString("product_id");
              prod_quantity[i] = item.getString("product_id");



          }
      }catch (JSONException e1) {
          e1.printStackTrace();
      }


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


adapterProductPageFragment.addFragment(productPageFragment.newInstance

(i, prod_quantity [i]), prod_quantity [i]);}

          productViewPager.setAdapter(adapterProductPageFragment);
          unitTab.setupWithViewPager(productViewPager);

          highLightCurrentTab(0);

    }
  }

  private void highLightCurrentTab(int position) {




   productPageFragment.newInstance(position,
  adapterProductPageFragment.getPageTitle(position).toString());
    TabLayout.Tab tab=new TabLayout.Tab();

    for (int i = 0; i < unitTab.getTabCount(); i++) {
        System.out.println("In for loop------------");
         tab = unitTab.getTabAt(i);
        assert tab != null;
        tab.setCustomView(null);
        tab.setCustomView(adapterProductPageFragment.getTabView(i));

    }
    tab = unitTab.getTabAt(position);
    assert tab != null;
    tab.setCustomView(null);        
   tab.setCustomView(
  adapterProductPageFragment.getSelectedTabView(position));

   }

ProductPageFragment.java

  public class ProductPageFragment extends Fragment {

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

  public static ProductPageFragment newInstance(int position,String 
  title) {
    ProductPageFragment fragment = new ProductPageFragment();
    Bundle args = new Bundle();
    args.putInt("position", position);
    args.putString("title", title);
    System.out.println("Position and string"+position+"----"+title);
    fragment.setArguments(args);
    return fragment;
   }

   FragmentOfProducts.onClickListner monClickListner;
  @Override
  public void onAttach(Context context) {
    super.onAttach(context);
    monClickListner=(FragmentOfProducts.onClickListner) context;

  }
   public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {

            /*position = getArguments().getInt("position");*/

        selectedTabTitle=getArguments().getString("title");
    }
   }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup 
    container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

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

AdapterProductPageFragment.java

public class AdapterProductPageFragment extends FragmentStatePagerAdapter 
 {

int noOfTabs;
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();

private Context context;

public AdapterProductPageFragment(FragmentManager fm,Context context) {
    super(fm);
    this.context=context;
}


@Override
public int getCount() {
    return noOfTabs;
}



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

public void addFragment(Fragment fragment, String title) {
    /*Tab1Fragment.newInstance(title,"0");*/
    System.out.println("Add fragment"+fragment.getTag()+"---"+title);
    mFragmentList.add(fragment);
    mFragmentTitleList.add(title);

}

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

public View getTabView(int position) {
        View view = 
 LayoutInflater.from(context).inflate(R.layout.layout_for_unit_sku, 
 null);


        TextView tabTextView = view.findViewById(R.id.txt_unit);
        tabTextView.setText(mFragmentTitleList.get(position));
        tabTextView.setTextColor(ContextCompat.getColor(context, 
        R.color.whitetabs));
        tabTextView.setTypeface(custom_of_alegreyasans_regular);

        return view;
    }
    public View getSelectedTabView(int position) {
        View view = 
       LayoutInflater.from(context).inflate(R.layout.layout_for_unit_sku, 
       null);

        TextView tabTextView = view.findViewById(R.id.txt_unit);
        tabTextView.setText(mFragmentTitleList.get(position));
        tabTextView.setTextColor(ContextCompat.getColor(context, 
        R.color.white));
        tabTextView.setTypeface(custom_of_alegreyasans_bold);
        return view;
    }

}



tab.setCustomView(null); at this line shows error in main activity.

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: in.co.algotech.jars, PID: 9327
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.design.widget.TabLayout$Tab android.support.design.widget.TabLayout$Tab.setCustomView(android.view.View)' on a null object reference
        at in.co.algotech.jars.Home.ProductCardView.highLightCurrentTab)
        at in.co.algotech.jars.Home.ProductCardView.access$000
        at in.co.algotech.jars.Home.ProductCardView$getQuantity.onPostExecute
        at in.co.algotech.jars.Home.ProductCardView$getQuantity.onPostExecute
        at android.os.AsyncTask.finish(AsyncTask.java:695)
        at android.os.AsyncTask.access$600(AsyncTask.java:180)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:712)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7156)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:975)