How do I display the calendar date on the top of chat messages?

Question

I am working on a chat application but I am struggling to figure out how to display the calendar date on the top of chat messages; for example, something like this:

Answer 1

Vilen answer is right. I am just improving perfomance. Instead of doing view gone and visible for every view, we can add a text view programmatically when condition true.

ChatAdapter.java

public class ChatEGRecyclerAdapter extends RecyclerView.Adapter {

    public static class TextViewHolder extends RecyclerView.ViewHolder {
        public TextView textView;
        public LinearLayout timeText;
        public TextViewHolder(View v) {
            super(v);
            timeText = (LinearLayout) v.findViewById(R.id.timeText);
            textView = (TextView) v.findViewById(R.id.textView);
        }
    }

    private final List messages;


    public ChatEGRecyclerAdapter(List messages) {
        this.messages = messages;
    }


    // Create new views (invoked by the layout manager)
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item, parent, false);
        return new TextViewHolder(v);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
        final Message m = messages.get(position);
        final Context context = viewHolder.itemView.getContext();

        TextViewHolder holder = (TextViewHolder)viewHolder;
        holder.textView.setVisibility(View.VISIBLE);
        holder.textView.setText(m.getText());

        //Group by Date
        long previousTs = 0;
        if(position >= 1){
            Message previousMessage = messages.get(position-1);
            previousTs = Long.parseLong(previousMessage.getSentTime());
        }
        Calendar cal1 = Calendar.getInstance();
        Calendar cal2 = Calendar.getInstance();
        cal1.setTimeInMillis(Long.parseLong(messages.get(position).getSentTime())*1000);
        cal2.setTimeInMillis(previousTs*1000);
        boolean sameDay = cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR) &&
                cal1.get(Calendar.DAY_OF_YEAR) == cal2.get(Calendar.DAY_OF_YEAR);
        if (!sameDay) {
            TextView dateView = new TextView(context);
            dateView.setText(messages.get(position).getSentTime());
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT);
            params.gravity = Gravity.CENTER_HORIZONTAL;
            dateView.setLayoutParams(params);
            holder.timeText.addView(dateView);
        }
    }


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

}

Also time formatting and checking for every message is expensive. To minimize this code execution actually we can compare the time stamp while sending the message. Get the time stamp of last message and compare with current message. If greater than 24 hrs then send to the server with isNewGroup:true. Then populating adapter can done without time comparison like below.

@Override
    public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
        final Message m = messages.get(position);
        final Context context = viewHolder.itemView.getContext();

        TextViewHolder holder = (TextViewHolder)viewHolder;
        holder.textView.setVisibility(View.VISIBLE);
        holder.textView.setText(m.getText());

        if (messages.get(position).getIsNewGroup()) {
            TextView dateView = new TextView(context);
            dateView.setText(messages.get(position).getSentTime());
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT);
            params.gravity = Gravity.CENTER_HORIZONTAL;
            dateView.setLayoutParams(params);
            holder.timeText.addView(dateView);
        }
    }