RecyclerView：onBindViewHolder item.get（位置）的空对象引用[重复]

Question

我得到一个空指针异常，我认为这可能与 onBindViewHolder() 方法有关，因为我认为在调用 mItemAddFriends.get(position); 时我得到一个空对象；你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)

...

我的课程：

• 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()) 中的方法 bind() 的问题之外，一切正常。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

在您的 ItemViewHolder 类的绑定方法中为空。尝试从初始化“List mItemAddFriends”的位置进行调试，看看为什么它有一个空值。