使用Linkedlist时不显示RecyclerView元素

我正在使用recyclerview显示cardview元素,并为其制作了一个适配器。当我使用Arraylist存储值时,recyclerview按预期工作,元素显示出来。然而,我想使用链表,因为项目会不断添加和删除。当我尝试使用链表时,recyclerview不起作用,元素也不显示。我怎样才能解决这个问题? 我的班级代码:

public class AdminViewAlertsActivity extends AppCompatActivity {
    RecyclerView recyclerView;
    DatabaseReference database;
    AlertAdapter alertAdapter;
    ArrayList<AlertModel> list;
    LinkedList<AlertModel> list2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_view_alerts);

        recyclerView = findViewById(R.id.alerts_list);
        database = FirebaseDatabase.getInstance().getReference("Alerts");
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        list = new ArrayList<>();
        list2 = new LinkedList<>();
        alertAdapter = new AlertAdapter(this,list2);
        recyclerView.setAdapter(alertAdapter);


        database.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                for (DataSnapshot dataSnapshot:snapshot.getChildren()){
                    AlertModel alertModel = dataSnapshot.getValue(AlertModel.class);
                    list.add(alertModel);
                    alertAdapter.notifyDataSetChanged();
                }
                alertAdapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });
    }
}

我的适配器代码:

public class AlertAdapter extends RecyclerView.Adapter<AlertAdapter.AlertViewHolder> {
    Context context;
    LinkedList<AlertModel> list;
    AlertAdapter adapter;

    public AlertAdapter(Context context, LinkedList<AlertModel> list) {
        this.context = context;
        this.list = list;
        this.adapter = this;
    }

    @NonNull
    @Override
    public AlertViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(context).inflate(R.layout.alrtitem,parent,false);
        return new AlertViewHolder(v);
    }

    interface Interactions{
        public void refreshActivity();
    }

    @Override
    public void onBindViewHolder(@NonNull AlertViewHolder holder, int position) {
        AlertModel alertModel = list.get(position);
        holder.date_and_time.setText(alertModel.getDate_time());
        holder.alert.setText(alertModel.getNotification());
        holder.viewOptions.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                PopupMenu popup = new PopupMenu(context, holder.viewOptions);
                popup.inflate(R.menu.alertmenu);
                popup.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
                    @Override
                    public boolean onMenuItemClick(MenuItem menuItem) {
                        switch (menuItem.getItemId()){
                            case R.id.alertmenu1:
                                DatabaseReference dataRef = FirebaseDatabase.getInstance().getReference();
                                dataRef.child("Alerts").child(alertModel.getDate_time()).removeValue().addOnCompleteListener(new OnCompleteListener<Void>() {
                                    @Override
                                    public void onComplete(@NonNull Task<Void> task) {
                                        Toast.makeText(context, "Removed", Toast.LENGTH_SHORT).show();
                                        list.remove(holder.getBindingAdapterPosition());
                                        adapter.notifyDataSetChanged();

                                    }
                                });
                            default:
                                return false;
                        }
                    }
                });
                popup.show();
            }
        });

    }

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

    public static class AlertViewHolder extends RecyclerView.ViewHolder{

        TextView date_and_time, alert, viewOptions;

        public AlertViewHolder(@NonNull View itemView) {
            super(itemView);
            date_and_time = itemView.findViewById(R.id.date_and_time);
            alert = itemView.findViewById(R.id.Alert);
            viewOptions = itemView.findViewById(R.id.viewOptions);
        }
    }


}

感谢您的帮助!