使 RecyclerView 中的项目可点击时出现问题

Question

我知道有这样的问题，但没有解决我的..我正在尝试将 'RecyclerView' 设为 'OnItemClickListener' ，但是当我运行该应用程序时，它停止了。你能告诉我错误在哪里吗？这是代码：（请注意错误在于使项目可点击）public class TeacherActivity extends AppCompatActivity {private FirebaseAuth mAuth=FirebaseAuth.getInstance();private FirebaseUser currentUser= mAuth.getCurrentUser();;private FirebaseFirestore db = FirebaseFirestore.getInstance();private String UserId =currentUser.getUid();private static String city;private TeacherAdapter teacherAdapter;public static final String EXTRA_PATH = "com.example.exercise.EXTRA_PATH";@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_teacher);    setUpRecyclerView();  teacherAdapter.setOnItemClickListener(new TeacherAdapter.OnItemClickListener() {  @Override  public void onItemClick(DocumentSnapshot documentSnapshot, int position) {    String path = documentSnapshot.getReference().getPath();    Intent intent = new Intent(TeacherActivity.this, SecondActivity.class);    intent.putExtra(EXTRA_PATH, path);    startActivity(intent);    }    });}// end of onCreateprivate void setUpRecyclerView(){    Query query =   db.collection("Teachers");    FirestoreRecyclerOptions < Teacher > options = new     FirestoreRecyclerOptions.Builder<Teacher>()                            .setQuery(query, Teacher.class)                            .build();    teacherAdapter = new TeacherAdapter(options);    RecyclerView recyclerView = findViewById(R.id.recycler_view);    recyclerView.setHasFixedSize(true);    //for performane reasons    recyclerView.setLayoutManager(new LinearLayoutManager(this));    recyclerView.setAdapter(teacherAdapter);    teacherAdapter.startListening();}@Overrideprotected void onStart() {    super.onStart();}@Overrideprotected void onStop() {    super.onStop();    teacherAdapter.stopListening();}}// end of class

Answer 1

您收到以下错误：

E/AndroidRuntime：致命异常：主进程：com.example.exercise，PID：29966 java.lang.RuntimeException：无法启动活动 ComponentInfo{com.example.exercise/com.example.exercise.TeacherActivity}：java.lang。 NullPointerException：尝试在空对象引用上调用虚拟方法“void com.example.exercise.TeacherAdapter.setOnItemClickListener(com.example.exercise.TeacherAdapter$OnItemClickListener)”

因为您正在调用.setOnItemClickListener()当时的teacherAdapter对象。null要解决这个问题，您只需移动以下代码块：

teacherAdapter.setOnItemClickListener(new TeacherAdapter.OnItemClickListener() {

    @Override

    public void onItemClick(DocumentSnapshot documentSnapshot, int position) {

        String path = documentSnapshot.getReference().getPath();

        Intent intent = new Intent(TeacherActivity.this, SecondActivity.class);

        intent.putExtra(EXTRA_PATH, path);

        startActivity(intent);

    }

});

在声明适配器之后：

teacherAdapter = new TeacherAdapter(options);

按照你的setUpRecyclerView()方法，你的问题就会得到解决。