无法从列表视图中获取项目 position：尝试在 null object 参考上调用虚拟方法...

Question

I am trying to make a popup menu appear when I click one of the items on the ListView, but I cant get the position of the item.

        listax.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {

                ItemList item= adapter.getItem(position);

                Toast.makeText(getContext(), item.getTxtNomeItem().toString(),   Toast.LENGTH_SHORT).show();
                //showPopup(adapterView);

            }
        });

That code gives me "Attempt to invoke virtual method 'java.lang.Object com.example.securityaplication.ItemArrayAdapter.getItem(int)' on a null object reference" error.

I have made the same thing in another project and it worked fine:

        listax.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {

                modelo item = adapter.getItem(position);


                Toast.makeText(getApplicationContext(),
                        item.getNome().toString (), Toast.LENGTH_SHORT).show();

            }
        });

The only difference is that I used "getContext" instead of "getApplicationContext()" because it didnt accept "getApplicationContext()" and that the first one is in a fragment and the latter one is in a activity.

My Fragment where it gives me the error:

public class HomeFragment extends Fragment implements PopupMenu.OnMenuItemClickListener  {

    ItemArrayAdapter adapter;
    private ListView listax;


    public HomeFragment() {

    }
    
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {


        View view = inflater.inflate(R.layout.fragment_home, container, false);
        listax = (ListView)view.findViewById(R.id.listViewx);

        ArrayList<ItemList> ItemList = new ArrayList<>();

        ItemArrayAdapter itemArrayAdapter = new ItemArrayAdapter(getActivity(), R.layout.adapter_view_layout,ItemList);
        listax.setAdapter(itemArrayAdapter);
        


        listax.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {

                ItemList item= adapter.getItem(position);

                Toast.makeText(getContext(), item.getTxtNomeItem().toString(),   Toast.LENGTH_SHORT).show();
                //showPopup(adapterView);

            }
        });

        return view;
    }

    public void showPopup(View v){
        PopupMenu popup = new PopupMenu(getActivity(), v);
        popup.setOnMenuItemClickListener(this);
        popup.inflate(R.menu.menupopup);
        popup.show();
    }

    @Override
    public boolean onMenuItemClick(MenuItem menuItem) {
        switch(menuItem.getItemId()){
            case R.id.itemAlterar:
                Toast.makeText(getActivity(), "Item 1 clicked", Toast.LENGTH_LONG).show();
                return true;
            case R.id.itemExcluir:
                Toast.makeText(getActivity(), "Item 2 clicked", Toast.LENGTH_LONG).show();
                return true;
            case R.id.itemEmprestar:
                Toast.makeText(getActivity(), "Item 3 clicked", Toast.LENGTH_LONG).show();
                return true;
            case R.id.itemRecuperar:
                Toast.makeText(getActivity(), "Item 3 clicked", Toast.LENGTH_LONG).show();
                return true;
            default:
                return false;
    }}
}

Answer 1

Don't forget to use the class member variable "adapter" when you setup the ListAdapter.

//ItemArrayAdapter itemArrayAdapter = new ItemArrayAdapter(getActivity(), R.layout.adapter_view_layout,ItemList);
//listax.setAdapter(itemArrayAdapter);

adapter = new ItemArrayAdapter(getActivity(), R.layout.adapter_view_layout,ItemList);
listax.setAdapter(adapter);