Question

这是我们将调用FragmentClass方法的片段的父活动。片段类的引用显示空指针异常。

下面我们将看到从父活动开始的片段。

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;

        }
    }
}

现在我们调用片段类方法的方法。缺少一些与此问题无关的代码。

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

我也试过，manage = getSupportManager（）;并且没有fragmentVegetable.getM ....对象但fragment.setVegetableListItemZero（）始终显示空指针。那片段没有任何参考。

现在我将展示Fragment活动和名为。

的方法

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;
         }
     }
 }

还有一些其他代码与问题无关，并且工作正常。

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

这是log cat，其中发生空指针异常。

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

更改您的deleteProductmethod代码

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

从父活动调用Fragment方法时出现空指针异常

1 个答案: