Android- Firebase 数据未显示在 ArrayList 中

Question

我正在尝试从 Firebase 数据库中检索数据。顶级节点是消息，子节点是作者和消息。登录后，聊天消息将从数据库中提取。 ChatActivity 调用 ChatListAdapter使用以下代码:-

    mAdapter = new ChatListAdapter(this, mDatabaseReference);
    mChatListView.setAdapter(mAdapter);

这里的mChatListView是一个RecyclerView。适配器代码如下:-

    public class ChatListAdapter extends RecyclerView.Adapter<ChatListAdapter.ViewHolder> {
    private Activity mActivity;
    private DatabaseReference mDatabaseReference;
    private ArrayList<DataSnapshot> mSnapshotList;

    private ChildEventListener mListener = new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            mSnapshotList.add(dataSnapshot);
            notifyDataSetChanged();
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };

    public class ViewHolder extends RecyclerView.ViewHolder {
        TextView authorName, body;

        public ViewHolder(View view) {
            super(view);
            authorName = (TextView) itemView.findViewById(R.id.author);
            body = (TextView) itemView.findViewById(R.id.message);

        }
    }

    public ChatListAdapter(Activity activity, DatabaseReference ref) {
        this.mActivity = activity;
        this.mDatabaseReference = ref.child("messages");
        mDatabaseReference.addChildEventListener(mListener);
        mSnapshotList = new ArrayList<>();
    }

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

        return new ViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {

        InstantMessage message = getItem(position);
        String author = message.getAuthor();
        holder.authorName.setText(author);
        String msg = message.getMessage();
        holder.body.setText(msg);
    }

    public InstantMessage getItem(int i) {
        DataSnapshot snapshot = mSnapshotList.get(i);
        return snapshot.getValue(InstantMessage.class);
    }

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

ChatActivity 如下:-

    public class ChatActivity extends AppCompatActivity {

    private RecyclerView mChatListView;    
    private DatabaseReference mDatabaseReference;
    private ChatListAdapter mAdapter;

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

        mDatabaseReference = FirebaseDatabase.getInstance().getReference();           
        mChatListView = (RecyclerView) findViewById(R.id.chat_list_view);        
    }

    @Override
    public void onStart(){
        super.onStart();
        mAdapter = new ChatListAdapter(this, mDatabaseReference);
        mChatListView.setAdapter(mAdapter);
    }

    @Override
    public void onStop() {
        super.onStop();
        mAdapter.cleanUp();
    }
}

Answer 1

有两种方法可以解决这个问题。 <强> This 是一种推荐的方式，您可以使用 FirebaseRecyclerAdapter 和 this 从 Firebase 实时数据库检索数据并将其显示在 RecyclerView 中 是您可以使用 ArrayAdapter 的方式。

但请注意，为了使用这些答案，您需要添加 Firebase-UI 依赖项。参见 here最新版本。