android - 如何使用 firebase 按时间顺序显示聊天用户列表？

Question

我需要根据聊天用户使用 firebase 聊天发送给用户的最新消息来安排聊天用户。我试过使用基于时间戳的查询顺序，但它对我不起作用。请在下面找到我的代码和这里的数据库结构

   mDatabaseReference = FirebaseDatabase.getInstance().getReference();
                final Query databaseReference = FirebaseDatabase.getInstance().getReference().child(FirebaseConstants.USERS).child(mFirebaseUser).child(FirebaseConstants.COLLEGEMATES).orderByChild("timestamp");
                final DatabaseReference databaseReference1 = FirebaseDatabase.getInstance().getReference().child(FirebaseConstants.USERS);
                FirebaseRecyclerOptions<Student> options = new FirebaseRecyclerOptions.Builder<Student>().setQuery(databaseReference, Student.class).setLifecycleOwner(getActivity()).build();
                firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Student, FirebaseListViewHolder>(options) {
                    @Override
                    protected void onBindViewHolder(@NonNull final FirebaseListViewHolder holder, final int position, @NonNull final Student model) {
                        try {
                            databaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
                                @Override
                                public void onDataChange(final DataSnapshot dataSnapshot) {
}

Answer 1

我通过在使用此代码段添加的名为“createdAt”的每条消息中添加 child 来解决此问题:

            String patternForDateExtended = "yyyyMMddHHmmss";
            DateFormat dff = new SimpleDateFormat(patternForDateExtended);
            Date today = Calendar.getInstance().getTime();
            String timeString = df.format(today);
            String rightNowEverything = dff.format(today)+rightNow.get(Calendar.MILLISECOND);

例如，输出将是一个新月形数字，如 20190404132156825

然后用这个命令消息:

     myRef.orderByChild("createdAt").addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

// adding to the recycleview everything.


            }

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

            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            }

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

            }

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

            }
        });

希望对你有所帮助，继续编码:)