获取Firebaserecycler的适配器项目数

Question

我一直在尝试获取Firebaserecycler适配器的itemcount。我的目的是检测recyclerview是否为空，并采取相应的措施。

private void loadFriendList2() {
    Query query = FirebaseDatabase.getInstance()
            .getReference(Commonx.USER_INFORMATION)
            .child(Commonx.loggedUser.getUid())
            .child(Commonx.ACCEPT_LIST);

    FirebaseRecyclerOptions<User> options = new FirebaseRecyclerOptions.Builder<User>()
            .setQuery(query, User.class)
            .build();

    adapter = new FirebaseRecyclerAdapter<User, AllFriendViewHolder>(options) {
        @Override
        protected void onBindViewHolder(@NonNull final AllFriendViewHolder allFriendViewHolder, int i, @NonNull final User user) {
            allFriendViewHolder.all_friends_txt_user_email.setText(new StringBuilder(user.getEmail()));


            DatabaseReference referencex = FirebaseDatabase.getInstance().getReference().child(Commonx.USER_INFORMATION);

            Query newx = referencex.orderByChild("uid").equalTo(user.getUid());


            newx.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {


                    childs = getSnapshots().size();
                    Toast.makeText(HomeActivity.this, String.valueOf(childs), Toast.LENGTH_SHORT).show(); // it do prints the value of child if exits


                    if (dataSnapshot.exists()) {
                        for (DataSnapshot userx : dataSnapshot.getChildren()) {

                            if (userx.child("image").exists()) {
                                Picasso.get().load(userx.child("image").getValue().toString()).into(allFriendViewHolder.all_friends_profile_image);
                            }


                        }


                    }


                }

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

                }


            });


            allFriendViewHolder.setiRecycItemListerner(new IRecycItemListerner() {
                @Override
                public void onItemClickListener(View view, int position) {

                    //show tracking information

                    Commonx.trackingUser = user;

                    startActivity(new Intent(HomeActivity.this, TrackingActivity.class));


                }
            });

            allFriendViewHolder.all_friends_locate_image.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Commonx.userProfile = user;
                    startActivity(new Intent(HomeActivity.this, UserProfileActivity.class));
                }
            });


        }


        @NonNull
        @Override
        public AllFriendViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View itemView = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.layout_all_friends, parent, false);


            return new AllFriendViewHolder(itemView);
        }

        @NonNull
        @Override
        public User getItem(int position) {
            return super.getItem(position);
        }
    };


    adapter.startListening();
    recycler_friend_list.setAdapter(adapter);

    if (adapter.getItemCount() == 0) {

        Toast.makeText(this, "No users in the friend list", Toast.LENGTH_SHORT).show();
    }


}

以下代码确实打印child（假设1或2）的值。但是，如果我将其打印在适配器的花括号之外，它将始终将itemcount打印为0。

                    childs = getSnapshots().size();
                    Toast.makeText(HomeActivity.this, String.valueOf(childs), Toast.LENGTH_SHORT).show();

而且，尽管RecyclerView的itemcout填充了项目，但以下代码始终为0。

if (adapter.getItemCount() == 0) {

    Toast.makeText(this, "No users in the friend list", Toast.LENGTH_SHORT).show();
    Toast.makeText(this, String.valueOf(adapter.getItemCount()), Toast.LENGTH_SHORT).show();

}

而且，我已经将以下方法称为getItemCount（）。

        @NonNull
        @Override
        public User getItem(int position) {
            return super.getItem(position);
        }