How to update recyclerview from firebase realtime database for a chat app

Question

I am using recyclerview and firebase realtime database together to allow user to send messages to other users.When a message is sent I need to start that activity again to reload the updates.Is there anyway to do this automatically so that when the user clicks on send the message is displayed directly.

Action when send button is clicked

 sendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                String message = messageBox.getText().toString();
                if (message.equals("")){
                    Toast.makeText(privatemessageactivity.this, "You cant send an empty message", Toast.LENGTH_SHORT).show();
                }else{


                    messagedref.addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot snapshot) {
                            if (!snapshot.exists()){
                                messagedref.setValue(true);
                            }
                        }

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

                        }
                    });



                    Map<String,Object> mymessage = new HashMap<>();
                    mymessage.put("Image",myImage);
                    mymessage.put("Message",message);
                    sendmessageref.push().setValue(mymessage);
                }
            }
        });

Action to retrieve the data

sendmessageref.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                if (snapshot.exists()){
                    for (DataSnapshot snapshot1 : snapshot.getChildren()){
                        MessageClass ld = snapshot1.getValue(MessageClass.class);
                        list.add(ld);
                    }

                    adapter = new MessageAdapter(list);
                    recyclerView.setAdapter(adapter);
                }
            }

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

            }
        });

My adapter class and my ViewHolder class

public class MessageAdapter extends RecyclerView.Adapter<MessageAdapter.ViewHolder>{

        private List<MessageClass> list;

        public MessageAdapter(List<MessageClass> list) {
            this.list = list;
        }

        @NonNull
        @Override
        public MessageAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.messagelayout,parent,false);
            return new ViewHolder(view);
        }

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

            MessageClass ld = list.get(position);
            holder.message.setText(ld.getMessage());

            if (!ld.getImage().equals("noimage")){
                Glide.with(getApplicationContext()).load(ld.getImage()).into(holder.circleImageView);
            }else{
                Glide.with(getApplicationContext()).load(R.drawable.profile).into(holder.circleImageView);
            }

        }

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

        public class ViewHolder extends RecyclerView.ViewHolder{

            TextView message;
            CircleImageView circleImageView;

            public ViewHolder(@NonNull View itemView) {
                super(itemView);

                message = itemView.findViewById(R.id.messagesmessage);
                circleImageView = itemView.findViewById(R.id.messagespp);

            }
        }
    }

Answer 1

The whole purpose of using Firebase is that you don't have to explicitly reload the messages. If you use addValueEventListener instead of addListenerForSingleValueEvent, Firebase will keep listening for changes on the server, and will call your onDataChange again if there as any changes.

So a common way to keep your message list up to date is:

adapter = new MessageAdapter(list);
recyclerView.setAdapter(adapter);

sendmessageref.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        list.clear();
        for (DataSnapshot snapshot1 : snapshot.getChildren()){
            MessageClass ld = snapshot1.getValue(MessageClass.class);
            list.add(ld);
        }
        adapter.notifyDataSetChanged();
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        throw error.toException();
    }
});

The changes:

• Uses addValueEventListener instead of addListenerForSingleValueEvent so that it gets called both for the initial data and when there are changes.
• Create and assign the adapter outside of onDataChange, since you'll want to set the adapter only once, and then update its data.
• Clear the list in onDataChange, since we'll now get called multiple times, and each time we get a full DataSnapshot of all the relevant data.
• Notify the adapter of the new data, with adapter.notifyDataSetChanged() so that it can refresh the UI,.
• Implement onCancelled, because it's a bad practice to ignore possible errors.