How to display a date like Whatsapp on scrolling ListView

问题

How can I show dates in an app when I scroll the ListView like in WhatsApp?
See the below image for clarity:

When I scroll the ListView, the date gets displayed over the list.
If you still did not understand my question please open your WhatsApp, go to any group & start scrolling: you will see the date getting displayed for older texts.

回答1:

To show date like this screenshot, you can use

val firstVisiblePosition = layoutManager.findFirstVisibleItemPosition()
if (getDateFromFirebaseTime(messageArrayList[firstVisiblePosition].timestamp.toString().toLong()).isNotEmpty()) {
                tvDay.visibility = View.VISIBLE
                tvDay.text = getDateFromFirebaseTime(messageArrayList[firstVisiblePosition].timestamp.toString().toLong())
            } else {
                tvDay.visibility = View.GONE
            }

What I did here is get the index of first visible item of RecyclerView list, then from that index I get the timestamp of the message and show it in the TextView tvDay using the function getDateFromFirebaseTime()

Above code is added in ScrollListener's this method of RecyclerView

override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
            super.onScrolled(recyclerView, dx, dy)
            Log.d("scroll", "scrolling")
            //added here
        }

Note: Here tvDay is added in the XML where RecyclerView is available. RecyclerView and tvDay are same child of RelativeLayout and tvDay set as android:layout_centerHorizontal="true" to keep it in top center.

回答2:

            Calendar cal = Calendar.getInstance();
            SimpleDateFormat sdf = new SimpleDateFormat("dd-MMM-yyyy");
            String strDate = sdf.format(cal.getTime());
            today = new String[user.length()];
            yesterday = new String[user.length()];
            earlier = new String[user.length()];
            int t_counter = 0;
            int y_counter = 0;
            int e_counter = 0;
            for (int i = 0; i < user.length(); i++) {
                JSONObject c = user.getJSONObject(i);
                post = c.getString(TAG_TEXT).toString();
                date = c.getString(TAG_DATE).toString();
                time = c.getString(TAG_TIME).toString();

                if (strDate.equals(c.getString(TAG_DATE.toString()))) {
                    if (t_counter == 0) {
                        TextView tv = getTextView(lp, "Today");
                        myLayout.addView(tv);
                        t_counter = t_counter + 1;
                    }
                    View msgView = generateChatView(post, time);
                    myLayout.addView(msgView);

                }
                try {
                    temp = sdf.parse(c.getString(TAG_DATE.toString()));
                    c_date = sdf.parse(strDate);
                } catch (ParseException e) {
                    e.printStackTrace();
                }
                if (c_date.getTime() - temp.getTime() == 86400000) {
                    if (y_counter == 0) {
                        TextView tv = getTextView(lp, "Yesterday");
                        myLayout.addView(tv);
                        ;
                        y_counter = y_counter + 1;
                    }
                    View msgView = generateChatView(post, time);
                    myLayout.addView(msgView);
                }
                if (c_date.getTime() - temp.getTime() > 86400000) {
                    if (e_counter == 0) {
                        TextView tv = getTextView(lp, "Earlier");
                        myLayout.addView(tv);
                        e_counter = e_counter + 1;
                    }
                    View msgView = generateChatView(post, time);
                    myLayout.addView(msgView);
                }

            }

来源：https://stackoverflow.com/questions/39397127/how-to-display-a-date-like-whatsapp-on-scrolling-listview