Null Pointer Exception while calling Fragment method from parent activity

Question

This is the parent activity of the fragment from where we will call a method of FragmentClass. The reference to fragment class is showing a null pointer exception.

Below we will see the starting of fragment from the parent activity.

public class HomeActivity extends  FragmentActivity {
    RocketMandiModel modelObject = new RocketMandiModel();
    ViewPager viewPager = null;
    ViewFlipper homeActivityViewFlipper;
    ImageView homeImageView;
    ImageView shoppingCartImageView;
    ImageView accountImageView;
    ListView  listView ;
    Fragment fragmentFruits;
    Fragment fragmentVegetables;
    private TextView infoTextViewInShoppingCart;
    private TextView checkOutTextViewInShoppingCart;
    public List<OrderItemDetails> ordersList = new ArrayList<OrderItemDetails>();
    ShoppingCartAdapter adp;
    int vegetableID;

    View v;
    //private String username;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // check if someone is logged in or not

        setContentView(R.layout.activity_home);
        modelObject.initializeLists();
        setFlipper();
        setHomeImageView();
        setShoppingCartImageView();
        setAccountImageView();
        setTextViews();
        listView = (ListView) findViewById(R.id.products_orders_list_view_at_shopping_cart);

            viewPager = (ViewPager) findViewById(R.id.pager);
            FragmentManager fragmentManager = getSupportFragmentManager();
            viewPager.setAdapter(new MyAdapter(fragmentManager));

    }

    class MyAdapter extends FragmentStatePagerAdapter {

        public MyAdapter(FragmentManager fm) {
            super(fm);
        }
        /**
         * Return the Fragment associated with a specified position.
         *
         * @param position
         */
        @Override
        public Fragment getItem(int position) {
        if(position == 0){

            fragmentVegetables = new FragmentVegetables();
            Bundle args = new Bundle();
            args.putSerializable("key", modelObject);
            fragmentVegetables.setArguments(args);
            vegetableID = fragmentVegetables.getId();
            return fragmentVegetables;
        }
        if(position==1){
         fragmentFruits = new FragmentFruits();
                Bundle args = new Bundle();
                args.putSerializable("key", modelObject);
                fragmentFruits.setArguments(args);
                return fragmentFruits;
            }
            return null;

        }
    }
}

Now the method from where we are calling the fragment class method. There is some code missing in between which is not relevant to this question.

private void deleteProduct(int position){
    FragmentManager manager = fragmentVegetables.getFragmentManager();
    FragmentVegetables fragment = (FragmentVegetables)       manager.findFragmentById(vegetableID);
    fragment.setVegetableListItemZero(0);
}

I have also tried, manage = getSupportManager(); and also without fragmentVegetable.getM.... object but fragment.setVegetableListItemZero() always shows null pointer. That is fragment do not have any reference in it.

Now I will show the Fragment activity and the method called.

public class FragmentVegetables extends Fragment {
    private List<Vegetables> vegetablesList = new ArrayList<Vegetables>();
    private View v;
    private RocketMandiModel modelObject;
    List<Integer> vegetableQuantityList;
       public View onCreateView(LayoutInflater inflater, ViewGroup container , Bundle saveInstanceState) {   
             /**
              * I do not know how inflator and shit works, I learned it from you tube and it
              * just work.
              */
             v = inflater.inflate(R.layout.fragment_vegetables, container, false);
             setModelObject();
             populateVegetableList();
             populateVegetableListView();
             return v;
         }
     }
 }

There is also some other code, which is not relevant to the question and is working fine.

public void setVegetableListItemZero(int positionOfDeletedProduct){
    Toast.makeText(getActivity().getApplicationContext(),"This is working  :" , positionOfDeletedProduct);
}

This the log cat, where the null pointer exception occurs.

E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
    at com.thefuelcompany.rocketmandi.HomeActivity.deleteProduct(HomeActivity.java:291)
        at com.thefuelcompany.rocketmandi.HomeActivity.access$200(HomeActivity.java:27)
        at com.thefuelcompany.rocketmandi.HomeActivity$ShoppingCartAdapter$1.onClick(HomeActivity.java:254)
        at android.view.View.performClick(View.java:4293)
        at android.view.View$PerformClick.run(View.java:17535)
        at android.os.Handler.handleCallback(Handler.java:725)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:153)
        at android.app.ActivityThread.main(ActivityThread.java:5299)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$
        MethodAndArgsCaller.run(ZygoteInit.java:833)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

Change Your deleteProductmethod code

 private void deleteProduct(int position){
   if(fragmentVegetables!=null){
       fragmentVegetables.setVegetableListItemZero(0);
 }
}