Question

我得到一个空指针异常，在我看来可能与onBindViewHolder（）方法有关，因为我认为我在调用mItemAddFriends.get（position）时得到一个空对象;您可以在下面看到我的代码和类。

错误日志：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.pmp_vip.personachat.ItemAddFriends.getUsername()' on a null object reference
                  at com.pmp_vip.personachat.ItemViewHolder.bind(ItemViewHolder.java:19)
                  at com.pmp_vip.personachat.RVAdapter$override.onBindViewHolder(RVAdapter.java:31)

...

我的班级：

RVAdapter类：

public class RVAdapter extends RecyclerView.Adapter<ItemViewHolder> {
    private List<ItemAddFriends> mItemAddFriends;

    public RVAdapter(List<ItemAddFriends> mItemAddFriends) {
        this.mItemAddFriends = mItemAddFriends;
    }

    public void setmItemAddFriends(List<ItemAddFriends> mItemAddFriends{
        this.mItemAddFriends = mItemAddFriends;
    }

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

    @Override
    public void onBindViewHolder(ItemViewHolder itemViewHolder, int   position) {
        final ItemAddFriends item = mItemAddFriends.get(position);
        itemViewHolder.bind(item);
    }

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

    public void setFilter(List<ItemAddFriends> itemAddFriends) {
        mItemAddFriends = new ArrayList<>();
        mItemAddFriends.addAll(itemAddFriends);
        notifyDataSetChanged();
    }
}

ItemViewHolder类：

public class ItemViewHolder extends RecyclerView.ViewHolder {
    public TextView username_textView;
    public TextView name_textView;

    public ItemViewHolder(View view) {
        super(view);

        username_textView = (TextView)   view.findViewById(R.id.item_username);
        name_textView = (TextView) view.findViewById(R.id.item_name);
    }

    public void bind(ItemAddFriends itemAddFriends) {
        username_textView.setText(itemAddFriends.getUsername());
        name_textView.setText(itemAddFriends.getName());
    }
}

AddFriendsActivity类：

public class AddFriendsActivity extends AppCompatActivity implements     SearchView.OnQueryTextListener {

    private RecyclerView recyclerView;
    private List<ItemAddFriends> mItemAddFriends;
    private RVAdapter adapter;

    private static final String SERVER_ADDRESS = "http://10.0.2.2/";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_friends);

       getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        mItemAddFriends = new ArrayList<>();

        recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);
        adapter = new RVAdapter(mItemAddFriends);
        recyclerView.setAdapter(adapter);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.add, menu);
        final MenuItem item = menu.findItem(R.id.action_add);
        final SearchView searchView = (SearchView)       MenuItemCompat.getActionView(item);
        searchView.setMaxWidth(Integer.MAX_VALUE);
         searchView.setQueryHint(getResources().getString(R.string.e_username));
        searchView.setIconified(false);
        searchView.setOnQueryTextListener(this);
        searchView.setOnCloseListener(new SearchView.OnCloseListener() {
            @Override
            public boolean onClose() {
                finish();
                return true;
            }
        });

        MenuItemCompat.setOnActionExpandListener(item,
                new MenuItemCompat.OnActionExpandListener() {
                    @Override
                    public boolean onMenuItemActionCollapse(MenuItem item) {
                        adapter.setFilter(mItemAddFriends);
                        return true;
                    }

                    @Override
                    public boolean onMenuItemActionExpand(MenuItem item)   {
                        return true;
                    }
                });
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                finish();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public boolean onQueryTextSubmit(String query) {
        return false;
    }

    @Override
    public boolean onQueryTextChange(String newText) {
        final List<ItemAddFriends> filteredItemList =  filter(mItemAddFriends, newText);
        adapter.setmItemAddFriends(filteredItemList);
        adapter.setFilter(filteredItemList);
        return true;
    }

    private List<ItemAddFriends> filter(List<ItemAddFriends> list,  String query) {
        query = query.toLowerCase();
        final List<ItemAddFriends> filteredItemList = new ArrayList<>();

        SearchUser searchUser = new SearchUser(query);
        searchUser.execute();
        filteredItemList.add(searchUser.getItemAddFriends());

       return filteredItemList;
    }

    private class SearchUser extends AsyncTask<Void, Void, Void> {

        String query;
        ItemAddFriends itemAddFriends;

        public SearchUser(String query) {
            this.query = query;
        }

        public ItemAddFriends getItemAddFriends() {
            return itemAddFriends;
        }

        @Override
        protected Void doInBackground(Void... params) {
            String jsonData = "";
            String result = "";
            JSONObject object = null;

            try {
                OkHttpClient client = new OkHttpClient();

                FormBody.Builder builder = new FormBody.Builder()
                        .add("query", query);

                RequestBody formBody = builder.build();

                Request request = new Request.Builder()
                        .url(SERVER_ADDRESS + "search.user.php")
                        .post(formBody)
                        .build();

                Response responses = null;

                try {
                    responses = client.newCall(request).execute();
                    jsonData = responses.body().string();
                } catch (IOException e) {
                    e.printStackTrace();
                }

                try {
                    JSONObject Jobject = new JSONObject(jsonData);
                    JSONArray Jarray = Jobject.getJSONArray("users");

                    for (int i = 0; i < Jarray.length(); i++) {
                        object = Jarray.getJSONObject(i);
                        result = object.getString("firstname");
                   }

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

            itemAddFriends = new ItemAddFriends(result, result);

            return null;
        }
    }
}

我认为除了ItemViewHolder类name_textView.setText（itemAddFriends.getName（））中方法bind（）的问题外，一切都有效;导致空指针异常。我不知道如何解决它。

感谢您的帮助!!

Answer 1

itemAddFriends

ItemViewHolder类的bind方法中的

为null。尝试从初始化＆＃34; List mItemAddFriends＆＃34;的位置进行调试，并查看它为什么具有空值。

RecyclerView：onBindViewHolder上的空对象引用item.get（position）

1 个答案: