数据显示在火灾基础控制台中，但未出现在模拟器中

Question

我创建了fire base实时数据库项目并尝试在Recycler View中显示学生列表，数据通常出现在fire base console中但是没有出现在模拟器中？

这是Recycler View类代码：

public class StudentAdapter extends RecyclerView.Adapter<StudentAdapter.StudentHolder> {
private Context context;
private List<Student> studentList;

public StudentAdapter(Context context, List<Student> studentList) {
    this.context = context;
    this.studentList = studentList;
}

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

@Override
public void onBindViewHolder(StudentHolder holder, int position) {
    final Student student = studentList.get(position);
    holder.studentNameTv.setText(student.getName());
    holder.studentAvgTv.setText(String.valueOf(student.getAverage()));

    holder.editStudentBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(context, EditStudentActivity.class);
            intent.putExtra("name", student.getName());
            context.startActivity(intent);
        }
    });


    holder.deleteStudentBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            final FirebaseDatabase database = FirebaseDatabase.getInstance();
            DatabaseReference ref = database.getReference();
            Query query = ref.child("students").orderByChild("name").equalTo(student.getName());

            query.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        snapshot.getRef().removeValue();
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }
    });
}

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

class StudentHolder extends RecyclerView.ViewHolder {
    TextView studentNameTv, studentAvgTv;
    Button deleteStudentBtn, editStudentBtn;

    public StudentHolder(View itemView) {
        super(itemView);
        studentNameTv = (TextView) itemView.findViewById(R.id.student_name);
        studentAvgTv = (TextView) itemView.findViewById(R.id.student_avg);
        deleteStudentBtn = (Button) itemView.findViewById(R.id.delete_student);
        editStudentBtn = (Button) itemView.findViewById(R.id.edit_student);


    }
}
}

以下是主要活动类代码：

public class MainActivity extends AppCompatActivity {
List<Student> studentList = new ArrayList<>();
StudentAdapter adapter;
DatabaseReference ref;

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


    final FirebaseDatabase database = FirebaseDatabase.getInstance();
    ref = database.getReference();

    ref.child("students").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
         studentList.clear();

            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                Student student = snapshot.getValue(Student.class);
                studentList.add(student);
                adapter.notifyDataSetChanged();
            }

            Collections.reverse(studentList);

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });


    final RecyclerView recyclerView = (RecyclerView) findViewById(R.id.rv);
    adapter = new StudentAdapter(MainActivity.this, studentList);
    recyclerView.setLayoutManager(new LinearLayoutManager(MainActivity.this));
    recyclerView.setAdapter(adapter);

    SearchView searchView = (SearchView) findViewById(R.id.search_view);
    searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String query) {
            Query fireQuery = ref.child("students").orderByChild("name").equalTo(query);
            fireQuery.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    if (dataSnapshot.getValue() == null) {
                        Toast.makeText(MainActivity.this, "ERROR", Toast.LENGTH_SHORT).show();
                    } else {
                        List<Student> searchList = new ArrayList<Student>();
                        for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                            Student student = snapshot.getValue(Student.class);
                            searchList.add(student);
                            adapter = new StudentAdapter(MainActivity.this, searchList);
                            recyclerView.setAdapter(adapter);
                        }
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
            return true;
        }

        @Override
        public boolean onQueryTextChange(String newText) {
            return false;
        }
    });

    searchView.setOnCloseListener(new SearchView.OnCloseListener() {
        @Override
        public boolean onClose() {
            adapter = new StudentAdapter(MainActivity.this, studentList);
            recyclerView.setAdapter(adapter);
            return false;
        }
    });
}
}