RecyclerView notifyDataSetChanged（）不起作用

Question

I'm using firebase for chat app and I'm implementing to fetch messages from firebase database and update recycler view.

When I click the "send" button, it acts like below.

button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        final ChatModel.Comment comment = new ChatModel.Comment();
        comment.uid = uid;
        comment.message = editText.getText().toString();
        FirebaseDatabase.getInstance().getReference().child("chatrooms")
                .child(chatroomUid).push().setValue(comment).addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void aVoid) {
                FirebaseDatabase.getInstance().getReference().child("chatrooms")
                        .child(chatroomUid).addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        comments.clear();
                        for(DataSnapshot item : dataSnapshot.getChildren()) {
                            if(item.getKey().compareTo("users")!=0) {
                                comments.add(item.getValue(ChatModel.Comment.class));
                            }
                        }
                        adapter.notifyDataSetChanged();
                    }

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

                    }
                });
            }
        });
    }
});

Process is like this.

1. Store message data into firebase database using "Comment" object form.
2. If stage 1 is succeeded, fetch that message and call notifyDataSetChanged()

But it is not working, I have global adpater object and above method is called by this variable.

Adapter code is like below.

private class messageRecyclerveiwAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item_message, viewGroup, false);
        return new MessageViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int i) {
        ((MessageViewHolder)viewHolder).textView.setText(comments.get(i).message);
    }

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

How can I fix it?

Answer 1

You need to create an object of your Adapter in the same class as you have the setOnClickListener:

Something like this:

final MessageRecyclerViewAdapter adapter = new MessageRecyclerViewAdapter(getActivity(), messageArrayList);

Then you need to pass the adapter to the method you're using to get the messages. Right now, you're calling notifyDataSetChanged() in the adapter which is wrong. First you need a specific method to get those messages from Firebase. For example:

public void getLiveChatMessages(final ArrayList<ChatMessageClass> messageArrayList, final MessageRecyclerViewAdapter adapter) {

I'm guessing you have a class that returns different part of the messages.. That's what I've named "ChatMessageClass" here, but you may call it something else. Within this method you get the messages from Firebase, then afterward you call as the last thing in the method:

adapter.notifyDataSetChanged();}

within the getLiveChatMessages method. Here you also pass in the adapter so that you can use it. This is the way to call the notifyDataSetChanged() within the same method as where you get the messages.

Good luck!